Gas Swimming Pool Heaters

Gas-fired pool heaters remain the most popular system for heating swimming pools. Today you can find new gas-fired heater models with much higher efficiencies than older models. Still, depending on your climate and pool use, they may not be the most energy-efficient option when compared to heat pump and solar pool heaters.

How They Work

Illustration of a gas pool heater. The heater is a large cube with horizontal vents down the two sides showing. Each of these sides also has a small panel with two round dials.

A gas pool heater. The heater is a large cube with horizontal vents down the two sides showing. Each of these sides also has a small panel with two round dials.

Gas pool heaters use either natural gas or propane. As the pump circulates the pool's water, the water drawn from the pool passes through a filter and then to the heater. The gas burns in the heater's combustion chamber, generating heat that transfers to the water that's returned to the pool.

They're most efficient when heating pools for short periods of time, and they're ideal for quickly heating pools. Therefore, gas pool heaters can be a good choice for pools that aren't used on a regular basis. Unlike heat pump and solar pool heaters, gas pool heaters can maintain any desired temperature regardless of the weather or climate.

Selecting a Gas Pool Heater

When selecting a gas swimming pool heater, you need to consider the following:


You should have a trained pool professional perform a proper sizing analysis for your specific swimming pool to determine pool heater size.

Sizing a gas pool heater involves many factors. Basically, a heater is sized according to the surface area of the pool and the difference between the pool and the average air temperatures. Other factors also affect the heating load for outdoor pools, such as wind exposure, humidity levels, and cool night temperatures. Therefore, pools located in areas with higher average wind speeds at the pool surface, lower humidity, and cool nights will require a larger heater.

Gas pool heaters are rated by Btu (British thermal unit) output. Outputs range from 75,000 Btu to 450,000 Btu.

Calculating Approximate Size

To calculate an approximate heater size for an outdoor swimming pool, follow these steps:

1Determine your desired swimming pool temperature.  ______°
2Determine the average temperature for the coldest month of pool use.- ______°
3Subtract the average temperature for the coldest month from the desired pool temperature. This will give you the temperature rise needed.= ______°
4Calculate the pool surface area in square feet. ______ sq.ft.
5Now use the following formula to determine the Btu/hour output requirement of the heater: 
 (Temperature Rise) X (Pool Area) X 12 = (Btu/hour output required)

The formula above is based on 1º to 1-1/4ºF temperature rise per hour and a 3-1/2 mile per hour average wind at the pool surface. For a 1-1/2ºF rise multiply by 1.5. For a 2ºF rise multiply by 2.0.


New gas swimming pool heaters have a standard test they go through to determine their energy efficiency based on their Btu (British thermal unit) output.

Heater efficiency is the ratio of usable output to energy input. For example, an 80%-efficient heater uses $80 worth of useful heat for every $100 worth of fuel. Therefore, it wastes 20% of the fuel.

Most gas pool heaters feature their efficiency percentage on their nameplates. A pool heater's manufacturer can also provide its efficiency percentage.

Today, you'll find some gas pool heaters with 89%–95% efficiency. The following table shows how much you can save for every $1,000 in annual pool heating costs by installing a gas pool heater that's 95% efficient.

Annual Savings by Gas Pool Heater Efficiency
For Every $1,000 in Annual Pool Heating Costs
Current Heater
Cost with 95%
Annual Savings
55% $580 $420
60% $630 $370
65% $685 $315
70% $735 $265
75% $790 $210
80% $840 $160

*For every $1,000 in annual pool heating costs


Here you'll find information to help estimate annual gas heating costs for an outdoor swimming pool and/or savings if you replace a gas pool heater with one that's more energy efficient.

The table below estimates annual costs by location, by water temperature, and with or without using a pool cover.

Costs of Outdoor Pool Gas Heating by Location
Figures based on a 1,000 square-foot, outdoor pool heated
with an 80% efficient natural gas heater at $.50 per therm
Location Season Temperature
78° 80° 82°
Miami 1/1–12/31 $2136 $2848 $3600
w/cover 1/1–12/31 $416 $584 $800
Phoenix 3/1–10/31 $1384 $1776 $2216
w/ cover 3/1–10/31 $96 $168 $256
Dallas 4/1–10/31 $1512 $1920 $2456
w/ cover 4/1–10/31 $184 $280 $408
Atlanta 4/1–10/31 $1704 $2248 $2880
w/ cover 4/1–10/31 $320 $424 $592
Los Angeles 5/1–10/31 $1864 $2376 $2904
w/ cover 5/1–10/31 $168 $304 $472
Kansas City 5/1–10/31 $1434 $1872 $2384
w/ cover 5/1–10/31 $288 $416 $544
New York 5/1–9/30 $1448 $1904 $2384
w/ cover 5/1–9/30 $208 $296 $400
Chicago 5/1–9/30 $1621 $2072 $2536
w/ cover 5/1–9/30 $216 $296 $384
Denver 5/1–8/31 $1757 $2120 $2498
w/ cover 5/1–8/31 $123 $168 $243
Boston 5/1–8/31 $1712 $2096 $2504
w/ cover 5/1–8/31 $232 $328 $461
Minneapolis 6/1–9/30 $1331 $1776 $2176
w/ cover 6/1–9/30 $192 $248 $384
San Francisco 6/1–8/31 $1560 $1856 $2168
w/ cover 6/1–8/31 $192 $320 $472
Seattle 6/1–8/31 $1525 $1784 $2056
w/ cover 6/1–8/31 $304 $424 $552

*Figures based on a 1,000 square-foot, outdoor pool heated with an 80% efficient natural gas heater at $.50 per therm.

If you're replacing a gas pool heater, you can use the following formula to determine your annual cost savings with a higher efficiency gas pool heater model:

The formula is current annual cost multiplied by one minus current efficiency divided by new efficiency.

Installation and Maintenance

Proper installation and maintenance of your gas pool heater can optimize its efficiency. It's best to have a qualified pool professional install the heater and even perform complicated maintenance or repair tasks.

Read your owner's manual for a maintenance schedule and/or recommendations. You'll probably need to tune up your pool heater annually. Also, scaling in the burner or heat exchanger may decrease efficiency over a period of time.

With proper installation and maintenance, gas pool heaters typically last five or more years.

Other Types of Pool Heaters

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