Swimming Pool and
Hot Tub Spa
By heating the pool or a spa just a few hours
each day, can extend the swimming season several weeks into the
spring and fall. In warmer climates, a heater can allow you to swim
all year round. Here is a glossary of basic terms that are commonly
used for gas fueled heaters.
unit. A unit of measurement used to define the capabilities of
heaters. One Btu is capable of raising the temperature of one
pound of water by one degree Fahrenheit.
||The component of
the heater where the combustion of fossil fuel takes place. In
a pool and spa heater, the burner is typically located in a
heater's combustion chamber.
||A valve that
maintains a constant flow of water through the heat exchanger,
thus preventing damage to heater components.
||The act or
process of burning - and technically described as "rapid
oxidation usually accompanied by heat and light."
||A type of heater
in which the heat produced by the burning of fossil fuels is
exchanged directly to water flowing through a heat exchanger.
These heaters use ignition systems of two basic types
Millivolt ignition, in which heat from a
continuous pilot is used to generate electrical energy that
opens and closes the main gas valve and operates the system's
safety controls; and
Automatic spark ignition (also known as
an intermittent ignition device, or IID), in which the pilot
is lit only during heater operation and requires an outside
electrical hook-up to spark the pilot and run the system's
control and safety devices.
ensuring that the heater shuts off for a period of time - say,
five to 15 minutes before the recirculation pump shuts off.
This switch allows the water to cool off the system before it
stops running, thus prolonging the life of the heat exchanger.
(Due to varying designs of combustion chambers, not all units
require use of a fireman switch.)
||A safety device
that prevents the heater from firing if there isn't adequate
water flow through the system.
||A manifold in a
heater that directs the flow of water into and out of the heat
||The ratio of
heater output and input. Heater output is energy, expressed in
BTUs, transferred to the water. Heater input is the energy
used to generate that heat. Heater efficiency is calculated by
dividing heater output by heater input.
||A device with
coils, tubes or plates that absorbs heat from any fluid,
liquid or air and transfers that heat to another fluid without
intermixing. Most common to the pool and spa industry is a
copper-finned heat exchanger.
built into the gas valve in a gas fired heater that controls
the gas input to the burners and combustion chamber.
||The natural drop
in water temperature as heat is transferred to the surrounding
air. The majority of heat loss in a pool or spa system flows
from the uncovered surface of a pool or spa.
||A component of
the temperature control system that limits the temperature of
water in the heater - no higher that 140 degrees in most.
||A method of
heating in which water temperatures are raised only when the
pool or spa is going to be used.
||The liquid form
of propane gas, a heavy hydrocarbon occurring naturally in
||A mixture of
gaseous hydrocarbons, chiefly methane, occurring naturally
underground, often in association with petroleum products.
fossil-fuel burner that is kept lit in order to light the
principal burner. In spark ignition heaters, the pilot is lit
only when the heat is being used. In a millivolt system, the
pilot is on continuously, and heat from the pilot's small
flame is used to generate low-voltage electricity to operate
the system's valves and safety controls.
||The component in
a millivolt system that transforms heat from the pilot into
electrical energy. Also referred to as a thermal coupling or
||A device that
will not allow the heater to fire unless there is adequate
water pressure in the system. A pressure switch must be
adjusted according to differences in the level of the water's
surface vs. the location of the heater.
powdery, carbonaceous substance created by an improper
air-fuel mixture in combustion of fossil fuels. Soot is the
by-product of incomplete combustion.
||A method of
heating whereby the water is maintained at a constant
between the desired water temperature and the temperature of
the surrounding air.
||A unit of
thermal measurement equal to 100,000 BTUs. This unit is
commonly used in gas billing by utility companies.
temperature-control device that shuts off the heater when the
water reaches the desired temperature. In a temperature
maintenance system, this device will activate the heating
system when the water drops below a set level.
responsible for the introduction of air for combustion in the
combustion chamber and for dispersal of the spent fossil fuel,
or flue products, into the surrounding air.
A typical gas-fueled heater uses natural or
propane gas as the heating fuel. The water enters through one port
of the front water header, then through the nine heat exchanger, and
then out of the other port. Most of the heaters, water goes through
at least four of the tubes and picks 6 to 9 degree F on each pass
before leaving the heater.
The exchanger tubes are made of copper due to
its excellent heat conductivity, there by transferring the heat
effectively to the water. The tubes have fins to absorb heat even
more efficiently and are topped with sheet metal baffles to retain
the heat. However, improper water chemistry can easily attack this
soft metal and dissolve it into the water.
There is a flow control assembly on the front
header. This spring-loaded valve is pressure sensitive, designed to
mix cool incoming water with hot outgoing water to maintain the
temperature. Temperature control is achieved by flow regulation
rather than direct temperature regulation. This design keeps the
outgoing water no more than 10 to 25 degree F above the temperature
of the incoming water. This prevents condensation and other problems
that greater temperature differentials would create. When water
temperatures are over 115 degree F, minerals suspended in water
deposit in the heat exchanger. The design of the unit is such that
it allows 100 gpm with 1 1/2 inch plumbing or 125 gpm with 2 inch
The other major component of the gas-fueled
heater is the burner tray. This assembly can be disconnected from
the cabinet for maintenance or inspection. Depending on the size of
the heater, there will be 6 to 16 burners, the last one having a
pilot mounted on it. Individual burners can be removed for
replacement. The combination gas valve regulates the flow of gas to
the burner tray and pilot and is itself regulated by the control
Gas-fueled heaters are divided into two
categories based on the method of ignition. They are millivolt or
standing pilot heaters and the other being electronic pilot heater.
Millivolt or Standing Pilot Heater
This type of heater has a pilot that is
constantly burning. The heat of the pilot is converted into a small
amount of electricity (750 millivolts) by a thermocouple, powering a
number of switches. Together, the control switches constitute a
control circuit. When electricity passes through the entire control
circuit, the main gas valve opens and the burner tray gets flooded
with gas. The gas is then ignited by the pilot. The temperature of a
pilot flame is more than 1,100 degrees F.
The control circuit is a series of safety
switch devices that test for various conditions in the heater to be
correct before allowing the electrical current to pass on to the
main gas valve and fire up the unit. Following the flow of
electricity, a control circuit includes the following items.
A simple heat-sensitive device that is located
on a ceramic holder near the front of the gas burner tray, is the
fuse link. If the heat becomes too intense, the link melts and the
circuit is broken, there by cutting the power in the circuit. The
most common cause of high temperatures in the tray are: the heat
built-up due to improper ventilation, debris in the tray that is
burning, or the low gas pressure which make he flame to roll over.
A small toggle-type switch, on the face of the
heater next to the thermostat control, is the on-off switch. Often
it is a remote switch. Manufacturers recommend that a remote on/off
switch for a millivolt heater should be located in 20 to 25 feet
proximity from the heater. This is because with less than 0.75 volt
passing through the control circuit, any loss of power caused by
heat loss, means that there might not be enough electricity to power
the gas valve when the circuit is completed. This is particularly
true on cold days when heat loss is greater. Another reason is that
as the thermocouple wears out, the electricity generated decreases,
there by reducing the power.
Many manufacturers now sell dual thermostat
heaters, so that when different temperatures for pool and different
temperatures for the spa are desired, then you just have to flick
the remote to the desired thermostat.
Thermostats are the ones that control
temperature. They fall into two categories: mechanical and
electronic. The mechanical thermostat is a rheostat dial connected
to a metal tube that is filled with oil. At its end is a slender
metal bulb, which can sense the temperature of the water coming out
of the heater. These thermostats are precisely calibrated but the
settings is by trial and error to achieve desired temperature due to
instillation variation. Pool heater thermostats generally are
color-coded around the face of the dial, showing blue at one end for
cool and red at the other end for hot.
Thermostats usually do not allow water in the
pool or spa to exceed 103 to 105 degree F, although they can be set
higher. Also, they do not generally register water cooler than 60
degree F, so if the water is cooler than that the heater will
continue to burn even if the thermostat is turned down. Therefore,
to be sure that a heater is off, turn it off from the switch.
The electronic thermostat uses an electronic
temperature sensor. These are more precise than mechanical types;
however, they are also not given specific temperatures, but rather
the cool to hot, blue to red graduated dials for settings.
High-limit switches are small, bimetal
switches designed to maintain a connection in the circuit as long as
their temperature does not exceed a predesigned limit, usually 120
to 150 degree F. The protection value is similar to the fusible link
and often two are installed in the circuit, one after the other, for
safety and to keep the heater performing as designed.
The first high-limit switch is usually a 135
degree F switch, and the other is a 150 degree F switch. Where the
fusible link detects excessive air temperatures, the high-limit
switch detects excessive water temperatures. They are mounted in dry
wells in the heat exchanger header. Sometimes a third switch, called
the redundant high-limit, is mounted on the opposite side of the
heat exchanger for added safety.
The pressure switch is a simple device at the
end of a hollow metal tube, which in turn is connected to the header
so that water flows to the switch. If there is inadequate water flow
in the header there will not be enough resulting pressure to close
the switch. Thus, the circuit will be broken and the heater will
shut down. Although preset by the factory for 2 psi, most pressure
switches can be adjusted to compensate for abnormal pressures caused
by the heater being located unusually high above or below the water
level of the pool or spa.
Automatic gas valve
The automatic gas valve is often called the
combination gas valve because it combines a separately activated
pilot gas valve with a main burner tray gas valve and sometimes a
separate pilot-lighting gas line combined with the pilot gas valve.
After the circuit is complete, the electricity activates the main
gas valve which opens, flooding the burner tray. The gas is ignited
by the pilot and the heater burns until the control circuit is
broken at any point, such as when the desired temperature is reached
and the thermostat switch opens, if the on/off switch is turned to
off, if the pressure drops, the pressure switch opens and breaks the
There are several different designs of
automatic gas valve. For millivolt-powered units, the terminal board
will have three terminals. Terminals 1 and 2 are the neutral and
positive lines from the pilot generator to start the control
circuit. When the circuit is complete, power arrives at terminal 3
which opens the main gas valve.
On 25-volt units, there is a pair of terminals
to power open the pilot valve and to return the current to the
common or neutral line of the intermittent ignition device. Another
pair of terminals power open the main gas valve and return the
current to the neutral line of the intermittent ignition device.
The gas plumbing of the automatic gas valve is
self-explanatory. The large opening (1/2or1/4 inch) on one end, with
an arrow pointing inward, is the gas supply from the meter. Note
that it has a small screen to filter out impurities in the gas, like
rust flakes from the pipe. The hole on the opposite end feeds gas to
the main burner. The small threaded opening is for the pilot tube
and a similar hole is for testing gas pressure. These are clearly
marked. Automatic gas valves are clearly marked with their
electrical specifications, model numbers, and most important,
Natural Gas or Propane. Black components or markings usually
All combination gas valves have on/off knobs.
On 25-volt units, the knob is only on or off. With standing pilot
units, there is an added position for pilot when lighting the pilot.
As a positive safety measure in most, you are required to push the
knob down while turning.
An electronic spark ignites the pilot when a
heater with electronic ignition is turned on. This in turn ignites
the gas burner tray in the same manner as described previously. In
all other respects, these heaters operate the same way as those
already discussed. Where the control circuit on the standing pilot
heater is powered by millivolts, the electronic ignition heater is
controlled by the same kind of circuit but is powered by 25 volts
Regular line current at 120 or 240 volts is
brought into the heater and connected to a transformer that reduces
the current to 25 volts. This voltage is first routed into an
electronic switching device called the IID (intermittent ignition
device), which acts as a pathway to and from the control circuit.
From here the current follows the same path through the same control
circuit switches as described previously.
When the circuit is completed the current
returns to the IID, which sends a charge along a special wire to the
pilot ignition electrode creating a spark that ignites the pilot
flame. The IID simultaneously sends current to the gas valve to open
the pilot gas line. When the pilot is lit, the heat generates a
current that is sensed by the IID through the pilot ignition wire.
This information allows the IID to open the gas line to the burner
tray, which is flooded with gas ignited by the pilot.
Versus Propane Gas
There is not much differences in heaters using
natural gas and those using propane gas. The gas valve is clearly
labeled Propane. Because of different operating pressures, the gas
valve is slightly different although it looks the same as a natural
gas model, as are the pilot light and the burner tray orifices. The
heater case, control circuit, and heat exchanger are all the same as
for a natural gas model. Most manufacturers make propane heaters in
standing pilot/millivolt models only.
Natural gas is lighter than air and will
escape if the burner tray is flooded with gas but not ignited for
some reason. The odor added to natural gas can be detected if you
are near by.
With propane, however, the gas is heavier than
air and if it floods the burner tray without being ignited it tends
to sit on the bottom of the heater. Because it remains undissipated
and cannot be detected by smell, if it ignites suddenly, it will do
so with violent, explosive force. Rarely is the heater itself
damaged-the explosion takes the line of least resistance, which is
out through the open front panel. Never position your face in front
of the opening and always use the safety checklist before trying to
detect any thing wrong in the system.
Electric heaters are used where gas heaters
are impractical and also when you are heating a spa. Because of the
cost of operation, the slower recovery and heating time, and the
high amps required with the corresponding heavy wiring and
electrical supply, electric heaters are useful in small portable
The components are similar to gas heaters
except the heat is derived from an electric coil that is immersed in
the water flowing through the unit. This is also true of the small
in-line electric heaters used in small spas. Often these in-line
units have no control circuits or they might have only a thermostat
control because the other controls are built into the spa control
Several sizes of electric heater are manufactured, rated by the
kilowatts consumed and, therefore, the BTUs produced. Here is a
comparison of the energy use and output of the most common models:
- 1.5-kilowatt (1500-watt) heater = 5119 Btu
- 5.5-kilowatt (5500-watt) heater = 18,750
- 11.5-kilowatt (11,500-watt) heater = 37,500
Each of these generally consume about
one-third more power to start up than to run at the designated
A solar heater transfers the heat of the sun
to the water. A typical solar installation consists of solar panels
from which the water should go before it passes through the heater.
In this way, some amount of heat can be gained from the sun first,
and then the gas heater adds additional heat if desired. Sensors
detect the heat on the panel and open motorized valves to divert the
water to the panels before it gets to the heater. If the panels are
cold, water flow will bypass the solar panels and go directly to the
Solar heating systems are controlled by time
clocks and/or thermostats because, in summer, the panels might add
too much warmth to the water and some means of regulation is needed.
They also have simple on/off toggle switches to completely disable
Most of the solar heaters work by cycling
water through solar collectors and back to the pool. These are
called open loop systems. They employ unglazed collectors, made from
plastic or metal, to absorb heat from the sun and transfer it to the
pool water. Other solar heaters employ glazed collectors, that
contain antifreeze fluid. As the fluid is heated, it is sent to
coils inside a heat exchanger, which then transfers the heat to the
pool water. These are called the closed loop type of systems. A
newer type of collector is made of Lexan with polycarbonate
The major manufacturers install and service
the units that they sell, so it is best to your benefit to
understand the design and have the warranty from the manufacturer.
Usually the solar heaters are mounted on the
roof, facing south. But with the flexibility of the designs
available today, the panels may not face directly south and can be
mounted on fences, shade structures garage roofs and slopes.
It is the heat pump in which heat is
transferred to that water by taking the warmth out of the air that
is created by compressing a gas. Pool and spa water circulates
through the unit the same way as the other heaters, but does not
pump any more heat than any other design of pool and spa heater.
A compressor in the unit exerts pressure on a
gas, usually Freon, and generates heat. The water is circulated
through a heat exchanger that is warmed by contact with the hot gas.
The gas cools from contact with the water and is recompressed and
heated to start the cycle all over again. The Freon used in heat
pumps is a nonflammable, noncorrosive gas, which makes it suited to
this application. Freon does not contain the chlorine component of
the Flourocarbon that makes it environmentally hazardous.
Though expensive, heat pumps are energy
efficient and last a long time. They are not effective spa heaters
because they take a long time to heat the water in the spa. Because
they rely in part on taking warmth from the air, the hotter the
surrounding temperature, the better and quicker they work.
Unlike gas-fueled heaters, heat pumps are
rated like air conditioners, expressed in tons. In this rating, a
ton is the amount of energy required to keep one ton of ice at 32°F
for 24 hours. As a rough rule of thumb, one ton equals 15,000 Btu.
These are not very common, and are designed
identically to gas-fueled units but they burn #2 diesel fuel instead
of natural or propane gas.
Three firms dominate the pool and spa heater
market-Raypak, Teledyne Laars, and Hydrotech (formerly Purex)-with
products that are remarkably similar. Several smaller companies
market spa heaters. For now you need to know that heater models are
based on their size as expressed in output of heat, measured in
BTUs. Each manufacturer produces models of similar size; for
example, 50,000, 125,000, 175,000, 250,000, 325,000, and 400,000
Teledyne Laars makes a good reliable unit with
almost everything in a convenient place inside the heater for easy
service work. They design the pilot assembly to be removed without
pulling out the entire burner tray.
The wiring for the transformer on the Teledyne Laars is located in
tight quarters behind the intermittent ignition device which is
inconvenient only when installing the original power hookup.
Raypak makes good heaters also. On their
electronic ignition models, the IID is hidden in a small compartment
that is accessed by opening the main panel first, then unscrewing
two or three upside-down-mounted screws to get into the second
compartment. This makes quick diagnosis a longer process when
troubleshooting repairs. Recently they have made this more
accessible, but there are a lot of the older models still in
Raypak burner tray design requires removing
the gas burner tray completely to work on the pilot assembly, and I
have had to pull it out and turn it upside down to get at tough
screws. Replacing the pilot is even tougher because the screws
holding it in place are very short.
Hydrotech/Purex heaters have not been as
popular as Teledyne Laars and Raypak, but their assembly and quality
is comparable. Numerous other companies make heaters in addition to
other equipment, but I find something comforting in working on
heaters made by companies that focus their attention only on
In my opinion, A.0. Smith made the best pool
and spa heaters ever built. Many are still in service and parts seem
to be readily available. They were over built everything was twice
as beefy and high-quality as it needed to be. As a result, they are
no longer made. Legend in the pool business has it that they
couldn't compete with the prices of the less expensive units on the
market today and they refused to compromise their quality, making it
no longer financially viable to build their units. Too bad, they
were great heaters.
I have one very wealthy customer who routinely
spends hundreds of thousands of dollars adding new cars to his
million dollar collection, but wouldn't part with his 20-year-old
A-0. Smith heater when the frequency of repairs suggested it was
indeed time to do so. instead, he wanted us to keep soldering the
old heat exchanger wherever it leaked and keep that baby running his
pool at 85 degrees F year-round. He still has it.
A few years ago it was true to say that each
manufacturer employed different designs but basically the same
components and concepts. In the past five years or so, they have
gone off in substantially different engineering directions so that
they can no longer be viewed generically. The basic concepts are,
however, the same, and Raypak, for example, has recently redesigned
its cabinets so that plumbing and gas connections are in the same
place as on Teledyne Laars (obviously to be more competitive when
replacing an old heater).
Other manufacturers, particularly the many
making small spa heaters or in-line portable electric spa heaters
are not mentioned here specifically because I have no particular
likes or dislikes among them, and many of them will be in or out of
business before the ink is dry on this page. As noted elsewhere
however, if you understand the concepts of one, you should have no
trouble with the others.
Because of frequent changes in engineering and
design, what I say here about a particular manufacturer might be
true about some models and not others. I have tried to make comments
based on the heaters I find most commonly in use today. While it is
important to understand the latest technology, it is more important
to understand the technology found in the most installations at the
While selecting a heater sizing and cost of
operation are the two basic parameters, besides the manufacturer
To find the unit with a cost and
energy-efficient source of heated pool or spa water, would be one
with the right size of heater, should heat the water to the desired
temperature, in the desired time frame. An undersized heater will
heat too slowly, and an oversized unit will do the job but will
increase the cost of the installation. Settling on just the right
heater therefore means satisfaction and leaves you with a
trouble-free heating system.
Depending on the need if the heater is going
to heat a pool or a spa, the thought process behind selection
differs for pools and spas.
In a pool, one of the primary factors used in
calculating heater size is heat loss from the surface. In a spa,
however, surface area is far less a factor, for spas are covered,
which greatly reduces surface heat loss. Instead, heat-up time
relative to the spa's gallonage is the critical factor.
Now you need to find out if the plans of using
the heater for maintenance heating or if they are only going to turn
on the burners occasionally for intermittent or spot heating.
Although calculating heater size for the two types of heating
strategies is basically the same, maintenance heating is typically
calculated using surface area, while heaters used for intermittent
heating often are sized by factoring total volume.
If you are not sure on this point, it
basically breaks down to a question of usage. If the pool is used
nearly every day during the swimming season or year-round, for that
matter, maintenance heating is the best strategy. If the vessel is
host to bathers only occasionally, however, it is far more
cost-effective to heat the water only when needed.
Another critical determination is what type of
heater to be put to use- natural gas, liquid propane or heating oil.
In some geographic areas, natural gas is either unavailable or
excessively expensive, making one of the other fuels more desirable.
You also need to know if there are codes in your area governing the
type of pilot-ignition system used in heaters. In some states,
continuous pilots (or millivolt systems) are banned for all new
installations. Intermittent ignition systems requiring an electrical
hookup are required in these jurisdictions.
It is also quite important to ascertain
whether the available utility hookup provides adequate pressure to
run the heater. Gas piping, meters and other delivery equipment must
be sized correctly to ensure an adequate gas supply.
Defining the variables
As is the case with just about every other
component in a pool or spa circulation system, there are variables
in heater sizing that you must address. Whether you use a
manufacturer's sizing chart or a generic heater sizing table, such
as those provided by the American Gas Association, you need to
gather and play with numbers to make the right choice. Here's the
data you need:
Surface area: The main job of a
vessel's heater is to offset the heat that is lost from the water's
surface, particularly for maintenance style heating. Here's a
rundown of the basic surface area calculations:
- Rectangular pool: length x width
- Oval pool: 1/2 length x 1/2 width x 3.14
- Rectangular pool with rounded ends: length
x width x .8
- Kidney-shaped pool: length x width x .75
Things get a bit trickier with free form
pools. Here, you must carefully draw an image of the pool's
perimeter on standard 1/4-inch grid paper. Using a scale of 1/8-inch
per foot, for example, means that each of the 1/4-inch squares on
the grid will equal two feet on each side, giving each grid square
an area of four square feet.
Next, you count the squares that fall entirely
within the drawn perimeter of the pool. Then count all of the
squares that fall approximately 3/4 within the surface area of the
pool as three square feet, those with half in the pool surface area
two square feet and so on. Add up the value of all of the squares on
Generic pool heater sizing chart temperature
maintenance (Outdoors 3.5 m.p.h. wind, surface area method)
Note: These heat losses are based on an
assumed wind velocity of 3-1/2 m.p.h. for a velocity of 5 m.p.h.
Multiply these losses by 1.25, and for 10 m.p.h. multiply by 2. 0.
Area ( Sq Ft)
Heater Output in BTUs/hr.
Volume: For spas and for pools in which
a spot-heating technique is to be used, total water volume is used
rather than surface area in calculating heater size.
To calculate volume, use the surface-area data
derived above and multiply it by the average depth, thus developing
a cubic-foot measurement of the vessel. To determine total gallonage,
multiply the pool or spa's cubic water footage by 7.5 the number of
gallons in a cubic foot of water.
Temperature rise: In most sizing charts
for pools, temperature rise is the primary factor along with surface
area or volume. Before you can determine temperature rise, however,
you must first peg the desired water temperature. For pools, the
American Red Cross recommends a range of 78-82 degrees Fahrenheit -
a range that seems to satisfy most bathers. In a spa, the
temperature should not exceed 104 degrees, as recommended by the
National Spa & Pool Institute.
Once you know the desired temperature, you
need to determine the average ambient air temperature. Most experts
recommend taking the average daily temperature during the coldest
month when the pool or spa will be used. When you subtract the
Ambient air temperature from the desired temperature, you've found
necessary temperature rise.
Heater efficiency: Expressed as British
thermal units (BTUs), heater output is the energy that a heater
transfers to the water. The heater input is the energy (again in
BTUs) used to generate that heat. Heater efficiency (HE) is the
ratio of the output to the input, expressed as a percentage. The
American Gas Association requires pool heaters have an efficiency
rating of at least 75 percent.
Heater-sizing charts often express the
required heater output necessary to achieve the desired temperature
rise for the pool's surface area or volume (see Figure 1 for a
generic example). Because heaters are rated by their input, however,
you must know the heater efficiency to determine what size heater is
required to do the job. In other words, if you multiply the required
output by .75, you will have the proper heater rating.
Manufacturers do part of the work for you in
their heating charts by replacing the required output with the
appropriate heater model number for the desired temperature rise and
surface area or pool volume.
Heat-up time: For spas especially, the
time required to heat the water to the desired temperature is
important when sizing the heater. Indeed, many spa heater sizing
charts use required heat-up time as a primary factor and assume a
given temperature rise.
For intermittent heating in pools, heat-up
time can be also very important, although many sizing charts simply
assume a 24-hour heat-up time.
Typical spa heater sizing intermittent
heating, gas, volume method, temperature rise of 30 degree F
Required for Each 30-Degree Temperature Rise
Plugging in the numbers Once you have
determined these key factors, selecting a heater is a simple matter
of plugging the numbers into sizing charts. Although they are
typically easy to use, the charts are formatted in varying ways.
Some plot the temperature rise on one axis with the pool volume on
the other. Here, you cross-reference these two key factors to
determine the proper heater output, which is listed in columns
across the chart.
Other charts, most of them provided by
manufacturers, list model numbers on one axis with the temperature
rise on the other. Cross-referencing the heater model with
temperature rise then leads you to pool sizes listed in columns on
the chart. Finally, some manufacturers offer easy-to-use sizing
slide rules. Here, you select the pool volume and temperature rise
to determine the model heater.
For spas, heat-up time often is the critical
factor. In these applications, sizing charts typically assume an
increase in water temperature - say, 30 degrees - with models (or
input ratings) listed on one axis and spa gallonage listed on the
other. Simply pick the spa volume and the desired heat-up time to
find the appropriate heater model or rating.
To determine the heater model on a chart that
lists required heater output, multiply the output by .75 to come up
with the heater input. (All heaters list their heater input ratings
on their faceplate and in specification manuals)
Helpful Tips For those who prefer to size the
heater based on their own calculations, the following formula is the
basis for most heater sizing charts used in the industry and can be
easily applied to either pools or spas:
Multiply the number of gallons by 8.33 (pounds
per gallon) by the temperature rise. The answer is the number of
BTUs required to heat the pool or spa.Here's an example using a
40-degree temperature rise in a 400-gallon spa - that is, 400 x 8.33
x 40 133,280 BTUs.
This number can either be divided by the
desired heat-up time to give you the required heater output, or it
can be divided by the heater capacity to give you the heat-up time a
given model will provide.
Let's assume, continuing the example above,
that you have a heater with an output of 266,000 BTUs. Here, 133,280
divided by 266,000 yields a heat-up time of .5 hours, or 30 minutes.
Conversely, if the customer has a specific heating time in mind say,
30 minutes - the formula works like this: 133,280 divided by .5
equals 266,000 BTUs. In other words, in a 400-gallon spa, you would
need a heater with an output of 266,000 BTUs to heat the water in 30
Variables involved When it comes right down to
sizing a heater, Sometimes it's not all numbers and formulas, but
also the location of the pool.
- Wind can dramatically increase the surface
heat loss from a pool or spa. By making waves across the water,
the wind effectively increases the surface area of the pool. The
rule of thumb: In a pool with an 11 mph wind you need to
increase the heater size by 25 percent.
- Altitude is another factor that calls for a
bigger heater: For each 1,000 feet above sea level, the heater
needs to be four percent larger.
- Shade also may lead you to a bigger heater.
Although there is no precise rule here, if the pool is located
in a shaded area, you should contact heater manufacturers, their
local representatives or your local supplier for expert
The heater model shows as to how many BTUs per
hour your heater uses. Dividing that by 100,000 gives how many
therms per hour it uses. A therm, the unit of measurement on the gas
bill. Thus it becomes easy to calculate the cost by multiplying with
the number of hour the heater works, which is usually 8 hours per
Making it clear by using an example, and
considering that the heater uses 135,000 Btu and the heater itself
being a 250,000 input Btu model. When you run it for eight hours a
day, then using the facts you have your operating cost calculated
250,000 Btu / 100,000 Btu/hour = 2.5
2.5 therms/hour x 8 hours/day = 20 therms/day
used to run the heater
20 therms/day x cost of cents/therm = total
In the spa if you use same 250,000-Btu heater
to heat the spa which would take an hour to do so. Using the same
calculations, you can calculate the cost to heat the spa. Of course,
the heater will run while the spa is in use and the heat loss will
be considerable as jets and blowers stir up the water, you have to
take this into consideration while calculating. To keep a standing
pilot burning, it uses between 1200 and 1800 Btu per hour and thus
the cost can be calculated in the same manner.
However, to calculate the true cost of
operating your pool or spa don't forget to add the cost of
electricity for pumps and motors, blowers, and other appliances.
For an oil-fueled heater the calculations can
be made on the umber of gallons that are used and one gallon equals
140,000 Btu. To calculate the cost for the gas utility units, you
have to know the amount of gas utilized by the heater itself and
then use the conversion factor, for electricity is sold by the
kilowatt-hour 1000 kilowatts consumed in one hour which equals 3412
There are so many possible combinations of
cause and breakdown for as many different types of heaters and
manufacturing designs that some basic guidelines for any heater
repair are listed here. Always remember to turn off the heater and
allow it to cool before starting to work on it.
It is generally better to replace well-worn
components rather than repair them. Also best is to get it repaired
by the manufacturers' serviceman.
To ensures years of trouble-free satisfaction
the heater should be properly installed. And to get the best job
done follow each manufacturer's own installation guidelines at the
jobsite. It consists of four basic steps like plumbing, gas,
electrical and most important location which includes ventilation.
The American National Standards Institute
offers guidelines - ANSI standard 2223.1- designed to keep the
heaters. This standard sets clearance requirements based on the
external temperatures of heaters, the following clearances may vary
from manufacturer to manufacturer.
The rear and non-plumbed sides of the heater
should have a minimum 6 inches of clearance. The water-connection
side should have a minimum of 18 inches of clearance. The front of
the heater should have at least 24 inches of clearance. Moreover,
the following clearances are based on the National Fuel Gas Code and
are universal for all gas-heater models. When installing a heater
under an overhang, there must be at least 3 feet of vertical
clearance from the top of the heater to the overhang, and the heater
must be open on three sides. The top of the heater must be at least
5 feet below or offset 4 feet from the nearest opening to a
building, such as a window or door; in addition, the top of the
heater must be at least 3 feet above any forced-air inlets located
within 10 feet of the unit.
All heaters must be installed at least 5 feet
from the inside wall of a spa unless it is separated from the spa by
a fence, wall or other permanent barrier.
Heating pad site
The heater must be installed on a level,
non-combustible base such as brick or concrete. If concrete cinder
block is used as a base, it must be aligned so the cells are all
pointing the same way; the end should be left open. When such hollow
masonry is used, the pad must be at least 4 inches high - and
covered with at least 24-gauge piece of sheet metal.
If the heater is placed in an area exposed to
high winds, the unit either must be installed at least 3 feet from
the nearest wall, or a windblock must be constructed to help
minimize the effect of wind.
The reasoning behind clearances and heating
pad site is to allow proper air flow around the heater, efficient
combustion and proper ventilation of the gas fuel.
Heaters installed indoors should follow
certain guidelines too:
If the heater is installed in a place where
vented air comes from another interior room, the space where the
heater is located must be connected to the additional airspace by
two vents, and the combined area of the space where the heater is
located and that additional room must represent at least 50 cubic
feet per 1,000 BTUs of heater input. The Btu input of any other
gas-burning appliances in that space, such as a home water heater,
must also be taken into consideration.
The space must have two openings, one
beginning 12 inches above the floor, the other t2 inches from the
ceiling. Each model of heater has specific venting requirements to
ensure proper combustion and prevent sooting. Manufacturers express
venting requirements as square inches of net free air. Consult
manufacturer charts for vent sizing requirements for the specific
model being used.
For spaces vented to the outside, the space
must also have top and bottom vents for the confined space. The
openings must connect directly or be connected by ducts to the
outdoors. Alternatively, the vents must connect to an area such as
an attic or crawl space connected directly to the outdoors.
All indoor heater installations require a
draft hood that sends combustion by-products - particularly carbon
monoxide - to the outside of the building. Failure to meet this
requirement can result in fire or carbon monoxide poisoning.
The diameter of the draft hood is based on the
National Fuel Gas Code and may vary from model to model. Connected
to the draft hood is the vent pipe, which vents products of
combustion to the outside air; it must have a diameter equal to or
greater than the draft hood.
The discharge opening in the vent pipe must be
at least 2 feet above the roof surface and must be at least 2 feet
above the highest point on the roof within a 10-foot radius of the
pipe location. The vent pipe must be topped with an approved vent
cap, which keeps wind and air from forcing products of combustion
back down into the ventilation system.
It is best to avoid horizontal piping runs as
much as possible. If horizontal runs are inevitable, the vent pipe
must have a minimum 1-inch rise for every foot of horizontal run and
must be supported at least every 5 feet. Avoid the 90 degree turns
Once venting needs are accommodated, you need
to consider whether the unit is getting an adequate supply of fuel.
For this, you need to look at the line running from the gas meter to
the heater and determine whether it is properly sized for the job.
Gas pressure is measured as inches of
water-column pressure, or WCP. Basically, WCP is a special measure
of pressure per square inch; it takes 28 inches of WCP to equal 1
psi. Generally, heaters running on natural gas require between 6 and
10 inches of WCP to ensure smooth performance. Heaters on liquid
petroleum require greater delivery pressures.
Heater manufacturers offer convenient
pipe-sizing charts for their customers, concentrating on sizes
between 3/4- and 1-1/2 inch diameters and working with runs of up to
Most heaters are fitted for operation at
altitudes of less than 2,000 feet above sea level. For guidance on
installations at higher elevations, you need to contact the
manufacturer for special, high-altitude models.
The basic installation requirements for the
gas connection are, a main gas-shutoff valve and union must be
installed within 6 feet of the heater and outside the heater jacket;
gas piping should have a sediment trap upstream of the heater's gas
controls; Rigid gas-line piping must be used. (Never use flex line
under any circumstances.)
The piping must be pressure tested once
installed. To conduct the test, the gas piping is disconnected from
the heater to avoid damaging the heater's gas-control equipment.
Here, the pipe is capped at the connection point and the gas turned
on, with a soap solution applied at all joints. (Never test for a
gas leak using a match or any other kind of flame.) Also, check for
additional testing requirements by some local codes.
If any bubbles form when the soap solution is
applied, there's a leak that must be repaired. Testing continues
until there are no leaks.
Some manufacturers also suggest using the
above procedure to test the burner and the pilot's tubing. In this
case, care must be taken to keep the test pressure below 10 inches
of WCP so as not to damage the gas control valve.
Controlling water temperatures
Properly locating the heater in the plumbing
is an obvious and important aspect of heater installation.
The heater should be installed downstream of
the pump and filter and ahead of any automatic chlorinating,
brominating or ozonating equipment. That is, the water should be
free of particulates or dirt when it enters the heater, and contact
with corrosive chemicals should be kept to a minimum by their
downstream placement. The heater should also be installed as close
to the pool or spa in the plumbing run as possible to prevent
unnecessary heat loss.
It is preferable to locate the heater level,
as close to level with the surface of the pool as possible. This is
because manufacturers preset their pressure switches for heater
installations that are typically 3 feet above or below the surface
of the pool. Consult the manufacturer's literature for specific
recommendations for elevated or sub-surface installations.
Manufacturer's literature provides either pipe
sizing charts based on desired flow rates and distance of the run or
specific pipe-sizing recommendations this makes sizing critical.
When using PVC piping, it is important to
position a heat sink between the heater and the piping - typically a
metal pipe approximately 2 to 4 feet long. For best performance of
the resulting PVC/metal connections, use a metal male fitting and a
PVC female fitting. Where allowed by codes and manufacturer's
instructions, high-temperature version of PVC (CPVC) can be
connected directly to the heater. To compensate for pipe expansion,
a flexible sealant should be used on all piping connections.
To avoid damage to plastic filter elements
that might be caused by back siphoning of hot water into the filter,
a check valve should be placed in the line between the filter and
the heater. Likewise, to prevent water with high concentrations of
chlorine or other sanitizing agents from backing up into the heater
and possibly corroding the heat exchanger, there should be a check
valve between any in-line chemical feeder and the heater.
The installation may or may not require use of
an external bypass valve and/or a pressure-relief valve. Be sure to
check the installation manual for a specific model's requirements
and other installation conditions that may require such control
Millivolt or continuous-pilot systems do not
require any electrical service to the heater. In order to enhance
energy conservation, however, some areas have required heaters to
use intermittent-ignition systems, which do require electrical
hook-ups or line voltage. For most applications, a qualified,
licensed electrician must perform or evaluate this part of the job -
from the circuit breaker panel to the heater.
Most heater models accommodate either 120-volt
or 240-volt power. The National Fuel Gas Code requires 14-gauge
copper wire for electrical service to gas heaters. Electrical wiring
should be run in waterproof conduit and hard-wired into the unit;
moreover, it should be run in its own conduit rather than in one
shared by timer or pump wiring.
If the circulation system is run with a timer,
the heater should be equipped with a separate low-voltage switch
that deactivates the heater before the pump is turned off. This
useful circuit is known as the heater's fireman switch. On a
millivolt heater, the length of wire between the heater and the
timer should not exceed 30 feet. Resistance on longer runs will
reduce the millivoltage to a level that will not support reliable
operation of the gas valve.
Finally, all such circuits require grounding
and bonding in accordance with the National Electric Code.
Gas heaters for pools and spas are more
complicated than filters, pumps or motors. Heater troubleshooting
resides in determining the problem's location within the system.
However, it is always necessary to consult each manufacturer's
service and maintenance manuals before troubleshooting a given
Heater can be a serious safety hazard, so if you are unsure about a
particular situation or procedure, ask an expert at your local
dealer or get help from the manufacturer.
Check the equipment room.
Check if the new unit has been installed
correctly according to the manufacturer's manual. Also check that
the inlet and outlet connections have not been reversed, during
renovation. Alternatively, if the heater is of the
intermittent-ignition device (IID) variety, the electrical hookup
may not be connected. Check the circuit breaker at the main power
panel and take the help of a licensed electrician. If it is an
indoor installation, always make sure the unit has an adequate
supply of outside air and all of the necessary venting.
Check the circulation system
The unit's safety devices will not allow it to
fire, if a heater is not getting proper water flow. A common problem
here is a dirty filter. So clean the filters, check the skimmer
basket, the main drain and the pump basket for blockages.
Check the fuel supply
Make sure the gas line and meter are properly
sized to provide adequate fuel to the heater. Then make sure the gas
shut-off valve on the heater is open. If the unit is running on
propane, be sure the tank has enough fuel.
Check the control settings
The top priority here is the thermostat, which
should be set to a temperature higher than the current temperature
of the pool or spa water. Note that the contacts in the thermostat
may be frozen, in which case they can usually be freed by moving the
control back and forth several times. Check the heater's toggle
switch. If the heater is on a time clock, it must be in the ON
position to operate.
Check the heater
If all of the above items check out, you
should begin to examine the heater itself. Note before we move on
that these are general guidelines; Techniques for troubleshooting
pilot, ignition and safety control circuits are presented only to
illustrate the logic behind heater troubleshooting; manufacturer
literature must always be consulted before approaching any specific
First, you must ascertain what type of pilot
the heater uses. There are two basic types; millivolt systems and
With the millivolt system, which we'll cover
first, the pilot is on continuously as a standing pilot; the heater
uses heat from that standing pilot to generate electricity to run
its safety, control and ignition systems. These millivolt systems
have no outside electrical hookups.
Millivolt pilot heater
Use a pocket mirror to see if the pilot is
burning; never put your face or eyes where you could possibly get
burned. It should be clean and free of obstructions.
Check the switches.
If the pilot lights and all of the external
functions and factors have checked out, the millivolt system's
inability to fire is likely to be the fault of a malfunctioning
component along the electrical path within the heater. At this
point, the suspect parts are the pressure switch, the high-limit
switch, the thermostat, the gas valve and the pilot generator.
The first step along this diagnostic line
involves sidestepping the gas valve by clipping a jump wire across
the valve's terminals. This enables you to bypass the chain of
control devices wired along the same circuit as the valve and to
check the performance of the gas valve and pilot generator. An
important reminder: After troubleshooting any component, always
remember to remove the jump wire.
- The control components you're bypassing -
the pressure switch, the thermostat and the high-limit switch -
are designed to prevent the gas valve from delivering gas to the
main burner when an unsafe or improper condition exists. To jump
the gas valve, connect one end of the jump wire to the terminal
connecting the thermostat and the gas valve, the other to the
connection between the gas valve and the pilot generator; these
may be labeled TH, TH-TP, thermostat or identified by color,
depending on the manufacturer. If the burner lights, you know
that the gas valve and pilot generator are good and that the
problem lies somewhere along the string of control devices. If,
however, the main burner doesn't light, you have either a
problem with the pilot generator, a wiring problem in
connections for the pilot generator or a bad gas valve.
Manufacturers offer specific diagnostic recommendations for
testing electrical current between these devices using a
voltmeter. Usually, the pilot generator's output should be above
500 millivolts with the circuit open - that is, when the heater
is not running. The connection between pilot generator and gas
valve, should read above 200 millivolts with the heater firing.
If it is below these levels, you probably have a bad pilot
generator; above that, the failure to light is usually
attributable to a faulty gas valve. Note, however, that a low
reading also may be the result of faulty wiring. Again, a
preliminary wiring check will help you avoid unnecessary effort
in troubleshooting these components.
- The next step in most units is to jump
across the pressure-switch terminals, thus electrically
bypassing the pressure switch. If the burners fire, then you
know that the pressure switch is not sensing proper water flow.
If you know there's proper flow in the system, then the switch
is either out of adjustment or defective. Consult manufacturers'
literature for adjustment procedures.
- If the burners do not fire when the
pressure switch is jumped, you move on to the thermostat. The
first thing to check is that the toggle switch is in the ON
position. Depending on the unit, the thermostat may need to be
removed from a mounting in order access its terminals. In any
case, the procedure is the same: Jump from one terminal on the
thermostat to the other. If the burners fire, then you have a
bad thermostat and it needs to be replaced. If they don't, you
need to move on.
- The last diagnostic step with millivolt
systems is a check of the high-limit switch or switches. If all
of the previous checks have been performed properly, then
jumping this switch (or set of switches) should result in the
heater firing. If you replace the high-limit switch and still
have a problem, check for proper water flow through the heat
IID pilot heater
Intermittent ignition devices differ from
millivolt devices chiefly in the fact that IlDs require an external
electrical source to power their functions. Here, the pilot is
sparked electrically only when it is needed to fire the burners.
As with the millivolt system, once external
checks have been made to your satisfaction, you can be fairly
certain the heater's failure to fire stems from a faulty component
in the control circuit.
Troubleshooting an IID control system calls
for an AC voltmeter with a 200-volt range or greater. As with the
millivolt system, you will be testing a series of components in
order to locate the faulty part. Set your voltmeter for the proper
voltage that is, above 24 volts.
Check the transformer. Attach one voltmeter
lead to one of the terminals for the system's 24-volt transformer,
then probe the other terminal with the second lead. When you make
contact with both terminals, you should get a reading of 20-28
volts. If the reading is low, you may have a voltage problem or a
Check the circuit. With the lead from the
voltmeter still in contact with the ground or common terminal on the
transformer, check for voltage along the circuitry starting with the
safety fuse, using the other lead of the meter as a probe. Then move
to the fusible link, the highlimit switch and the pressure switch.
If you have voltage at these points, the parts are good. If not, you
need to replace them.
Check the temperature control. Perform the
same test on the temperature control, making sure that the control
is in the ON position and that it is set to a temperature high
enough to call for heat. If there's voltage, the unit is fine. If
the heater is equipped with an electronic temperature control, the
control's sensor or probe should be checked following the procedures
recommended by the manufacturer.
Check the ignition control. When an IID heater
won't fire, the ignition control is another suspect. Electrically,
the ignition control is tested in the same fashion as the safety
devices. First, verify that it's receiving 20-28 volts. Then make a
visual inspection of the unit and test for a spark at the
pilot-burner electrode. Use caution around the electrode: It has low
amperage but a high voltage.
Moving on, check all electrical connections to
make sure they're tight. Make sure the igniter electrode has a
proper spark gap; this not unlike checking for the same in an
automobile spark plug. Consult manufacturer literature for a proper
Check for a spark. With the thermostat set
high enough to call for heat, you should have a spark at the
pilot-burner electrode if all of the controls are good.
If there is no spark, some manufacturers
recommend that you pull the wire off the ignition control and hold
it approximately an eighth of an inch away from the ground terminal.
If there is no arc across the space, the ignition control should be
replaced. If you do have a spark but the pilot doesn't light, a good
bet is that either you have a plugged pilot assembly or a bad gas
If a heater does not shut off
A heater that just won't shut off can be
particularly alarming. It may result in extremely high water
temperatures and constitutes an extreme danger. To get to the root
of such problems, you should check the gas valve. To do so, remove
the wire running between the gas valve and the thermostat. If the
heater doesn't shut off, you have a faulty valve that must be
replaced. If the heater does shut off, the gas valve is ok, but you
have a control problem. At this point, heater manufacturers
recommend that you bring in a specialist to troubleshoot the system
because of the seriousness of the problem.
Taking a quick look at some of the other basic
problems that you can come across with heater for pool and spa:
heater will not heat the pool or spa water to the desired
|The system is
not running long enough.
||Reset the time
|A dirty filter
is keeping the heater from firing.
is faulty or out of adjustment.
||Test and replace
the thermostat as needed.
switch is inoperative.
||Given a clean
filter, test the switch and replace it if necessary.
|The heater is
heater-sizing chart and upsize the unit.
|The gas system
sizing charts and upsize the plumbing.
||Check the meter
and the supply shut-off valve for proper sizing as well.
has formed in the combustion chamber
is flowing through the heater.
flow and clean the heat exchanger
|The air supply
installation for proper clearances and/or venting. (On indoor
applications, verify the adequacy of the air supply and
|The air inlet or
venturi for burner is plugged.
debris, dirt, in the sects or small animals in the burner
inlet's throat or venturi and clean them
|The time clock
prevents the heater from running long enough to heat the
||Adjust the time
clock clean the exchanger
|The gas valve
regulator is out of adjustment
||Test for proper
gas pressure and adjust the regulator as needed or replace the
Heater Goes On and Off Repeatedly
|The filter is
|The pool's water
level is low.
||Raise the water
bypass is out of adjustment.
switch is out
pressure switch of adjustment and verify that the heater shuts
off when the system's pump shuts off.
Scale is forming in the heat exchanger
|The pool or spa
water is excessively hard.
alkalinity, pH and calcium hardness within acceptable levels.
|The heater is
staying on when the water flow has diminished because of
debris in the filter
the pressure switch or the high-limit switch..
bypass valve is out of adjustment.
||Adjust or repair
the bypass valve.
Heat exchanger is corroding/ eroding.
chemistry is acidic..
||Check the bypass
valve as well as the pump sizing. You may need to install a
A lazy burner flame.
||Check gas pipe
and meter sizes and/or adjust gas pressure as needed.
|Debris, dirt or
insects are plugging the burners.
heater makes knocking or whining noises.
|The heater is
operating after the pump shuts off
replace the pressure switch.
|Debris or other
restrictions are blocking the system.
blockage and flush the system.
|Scale has built
in the heat exchanger's tubes.
replace the heat exchanger
switch is out of adjustment.
When a gas heater needs help, here is a
step-by-step guide to servicing its critical components.
The heat exchanger is where, as water
circulates through the exchanger's copper-finned piping, it is
warmed by hot air rising through the heater's structure from the
burners below. With good water balance as well as proper water flow
and venting a properly cared unit may last for years.
Occasionally, however, poor chemical
maintenance or improper water flow will damage a heat exchanger and
necessitate its replacement. The following covers the procedures
involved in switching out an exchanger as well as the steps involved
in another common service task: flipping the heat exchanger to
reorient its plumbing to the left rather than the right side.
Perhaps the biggest threat to the service life
of heat exchangers is improper water chemistry - particularly with
respect to pH.
Simply put, if your chemistry is too base -
that is, a pH above 7.8 with alkalinity above 120 parts per million
and calcium hardness above 400 ppm scale likely will form on the
inner surfaces of the heat-exchange tubing. This may reduce heater
efficiency and will certainly impede water flow.
In such cases, fixing the problem usually
requires reaming the exchanger's tubing with a carbide-tipped auger
followed by a soak in an acid/water solution and a good scrubbing.
If, on the other hand, the water is too acidic
- with a pH below 7.2, alkalinity below 80 ppm and calcium hardness
below 200 ppm - the water will corrode the exchanger. This will lead
to high copper content in the pool and eventually, if the water is
aggressive enough, will cause the exchanger to spring a leak.
Under such conditions - and depending upon the
degree of damage done to the exchanger - replacement is usually
Most heaters come with their inlet and outlet
ports on the right side, which means you'll occasionally need to
flip an exchanger to accommodate left-handed installations.
The following steps tell you the basics of
both these operations, including the extra steps involved in
flipping an exchanger. Note that this information is presented for
illustration purposes only; always consult manufacturer literature
for precise instructions and follow them carefully.
Down to business, step by step
Before digging into the heater itself, you
must make certain the circulation system is off. (Note: If you are
working on an intermittent-ignition device heater, cut the power at
the circuit breaker or time clock!) In addition, if the heater is
located below the surface level of the pool, check to make certain
the appropriate valves are in a closed position.
Now you're set to remove or flip the
exchanger: Disconnect the piping from the inlet and outlet fittings.
- Remove the faceplate and turn off the gas.
Most heater models include a tool-actuated latching mechanism
that requires just half a turn with a flat-head screwdriver.
After opening, turn off the gas at the gas valve. Once the gas
is off, the standing pilot in a millivolt system will
- Remove the control panel to access the
control wiring. (flipping only) These panels are attached with
screws - as are many other parts of the heater. Keep track of
these screws: Having a cup or other container on hand can be a
- Clip the nylon wire ties. (flipping only)
In flipping an exchanger, you will need to re-route some of the
control wiring from one side of the unit to the other. Clipping
the ties will give you the slack you need, but take care not to
cut into the wires' insulation.
- Remove the inner and outer flue collectors.
(A & B) These must be removed to permit access to the heat
exchanger through the top of the unit. After you unscrew them,
take care not to distort the shape of the collectors when
- Remove the faceplates. These plates are
positioned on both sides of the heater in front of the headers
and their plumbing connections.
- Remove the leads from the highlimit
switches. These connections are exposed once the faceplates are
- Remove the thermistor or thermostat sensing
bulb. A note of caution in removing thermistors. The graphite
paste used to enhance their temperature-sensing capability - a
gray, pastey substance - is very difficult to clean from your
hands and other heater parts. Experts recommend wiping the
thermistor clean with a rag when removing it.
- Disconnect the pressure switch and siphon
- Reposition the siphon loop and pressure
switch assembly on the other side of the heater. (flipping only)
In flipping an exchanger, you must reroute the connections for
these devices. Manufacturers stress that with proper care in
rerouting the wiring, you should not need to splice control
wires. Most heaters are designed with necessary brackets and
openings to accommodate flipping the heat exchanger.
- Lift the exchanger. With the headers still
connected, carefully lift the heat exchanger, making sure not to
bend or otherwise distort the mounting or "mud" clips.
- Inspect the fire blocks for cracks. If you
find fissures or cracks, replace the insulating panels.
- Turn the heat exchanger around. (flipping
only) Carefully reseat the unit in the opposite direction,
making sure it is firmly in place.
- Reconnect the pressure switch siphon loop
and the high-limit leads. (A & B) You do not need to switch
the high-limit leads from one side to the other. Reconnecting
the leads to the reversed headers does not affect the high-limit
- Reinsert the thermistor or sensor into the
header. A light coat of grease will adequately relace the
thermistor's graphite paste. Replace the thermistor's graphite
- Redress the wiring with nylon ties.
(flipping only) A tip: take up slack by coiling excess wire
around a Phillips-head screwdriver.
- Replace the faceplates. Making certain all
of the screws are in place before tightening any of them down,
remount the faceplates on both sides of the heater.
- Replace both the inner , and outer flue
collectors. (A & B) If exchanger replacement was your
objective, you're all done; if you are wrapping up the flipping
procedure, all you need to do to finish the job is to remount
the control-panel cover and replace the front door. Now all that
remains is initiating the circulation system and turning on the
gas. Always be sure to test heater functions and safety controls
per manufacturer instructions.
Using the heater regularly is the best
preventive maintenance. As noted previously, corrosion, insects,
nesting rodents, and wind-blown dirt create many heater problems
that can be eliminated by regular use. The heat helps to dry any
airborne moisture that might otherwise rust the components. It
discourages insects and rodents. It keeps electricity flowing
through the circuits, preventing corrosion that creates resistance
that might ultimately break the circuit completely. It burns off the
odd leaf or debris that lands inside the top vents there by
preventing fire. Running it for short period of times helps in
maintenance of the heater.
If not then, heaters need only be visually
inspected from time to time. A look around will detect sooting, gas
or water leaks, or other problems before they begin. You may open
the drain plug on the heat exchanger and look for scale buildup.
Keep leaves and debris off the top of the heater. Look at the pilot
and burner flames if they are strong, blue, and burning straight up
at least 2 to 4 inches.
The easiest way to work on heaters is to
maintain a simple kit of spare parts that save you a trip to the
supply house. It helps in troubleshooting as you can replace a part
you have doubts about in test. Having spares saves you time and
money and takes up little space in your toolbox.
Here's what you should have in your spare kit:
- A Scripto lighter
- Honeywell IID
- Millivolt pilot assemblies (including
generator); Clip-in type (Teledyne Laars) ; Screw-in type (Raypak);
Electronic pilot assemblies; Teledyne Laars style with bolt-on
electrode; Raypak style with clip-on electrode.
- Orange high-tension cords. Teledyne Laars
style with bare extension wire and ceramic - Raypak style
(longer) with clip on the end.
- Pressure switch with adapter for different
- Teledyne Laars set of high-limit switches
- Raypak set of high-limit switches
- Electronic thermistor
- Wire of various lengths and colors
(available with connectors in kits called harnesses)
- Teledyne Laars flange gaskets (1 1/2- and
- Raypak flange gaskets (1 1/2- and 2-inch
- Small dental-type mirror for examining
Generally, combination gas valves,
thermostats, and switches are too expensive, numerous, and varied to
carry as spares.
Spare parts on heaters are unbelievably
expensive. Building a heater from spare parts would cost three times
as much as buying a factory-assembled unit. As a result, many
companies now offer replacement parts that fit the popular brands of
heaters. Generally these generic brands work just as well as factory
replacements, although the factory won't necessarily agree.
To ensure an uninterrupted supply of parts,
manufacturers use parts from various suppliers or different models
of parts from the same supplier. A part might look different, but
that doesn't necessarily mean it is different. Examine it and ask
your supply house.
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