Gas Pool Heater

A gas pool heater is the most popular method of heating salt water pools and spas because of the speed and fuel efficiency when heating pool water to a warm and inviting temperature.  You will be able to create luxuriously warm water so you can swim into the night time hours and extend your pool season into the cooler months of the year. 

gas pool heater

Whether you are a salt water pool owner or a regular chlorine pool owner we will provide some important information about how to extend the life of your heater.  We'll talk about adding a sacrificial anode to prevent corrosion and the importance of keeping your pool balanced so you don't get any calcium buildup which could lead to decreased efficiency and potential damage. 

A gas pool heater will cost on average about 50% less to operate than electric heat pump heaters if you live in a cooler climate either in the northern United States or Canada.  A gas heater is recommended instead of an electric pool heater for pool owners that live in these regions.  Heat pump electric heaters are most efficient in warmer temperatures due to how they operate by drawing heat energy from the air to produce energy. 

Pool heaters that use gas are fueled by either natural gas through a gas line or propane from a canister tank.  In recent years gas heaters have become increasingly efficient and environmentally friendly with innovations in heat exchange technology and pilot-less ignition systems that have increased their efficiency upwards of 95%.

We will talk more about how a gas pool heater works including how to calculate BTU's or British Thermal Units so you can purchase a heater that will adequately heat your pool with the most efficiency.  After you know how to calculate the right size heater for you pool we'll provide our list of the best gas pool heaters for salt water pool owners

How a Gas Pool Heater Works

All gas heaters either use natural gas or propane to produce a flame that heats the metal exchange tubes.  The water from your pool flows through the heater and is warmed by the exchange tubes.  As this warm water returns to your pool it raises the overall temperature over a certain period of time.  A natural gas pool heater and propane pool heaters are both excellent for fast, short term heating and provide the most intense heat.  

If you live at an altitude of 2,000 feet above sea level or higher you will need a heater specifically designed for high altitude operation.

Gas pool heaters are rated by BTU output which is the amount of energy transferred to heat energy.  The US Department of Energy has regulated pool heaters to have an efficiency rating of at least 78%.  This means that a heater with 200,000 BTUs and an 85% efficiency rating would produce 170,000 BTUs per hour.

The BTU output is important in determining the size of heater required to heat your pool.  The ideal rating is dependant on the surface area of your pool where the larger the surface area of your pool is the higher BTU output required.  All pool heaters have a BTU rating and will be listed prominently by the manufacturer. 

A tip when shopping for a heater is to consider a 10% higher BTU rating than required just to be sure you have adequate heating during times of higher demand and at the beginning and end of the season.  If you purchase a larger heater you will heat your pool faster, use it less often and potentially increase the life of your heater.  

Another thing to consider is the difference between millivolt and electronic starters.  A millivolt starter uses a pilot light that must stay on constantly to initiate the heating process.  An electronic starter eliminates the need for a pilot light and will save you money over time and possibly the hassle of having to relight the pilot light found in a millivolt starter.

Gas Pool Heater Sizing

There are a couple quick calculations you will need to make to figure out the amount of BTUs required to heat your pool adequately.  We will walk you through it and at the end you will know exactly what size of heater to purchase for your specific pool.  The first thing you need to figure out is the surface area of your pool and this can be done by the simple equation below. 

  • Rectangular Pools:  Length x Width
  • Round Pools:  Radius x Radius x 3.14
  • Oval Pools:  ½ Length x ½ Width x 3.14


  • Rectangle Pool 15 ft x 30 ft = 450 sq ft in area
  • Round Pool 20 ft wide = 10 x 10 x 3.14 = 314 sq ft in area

After you have used these calculations to figure out the surface area of your pool you can determine the approximate amount of BTUs required to heat your pool sufficiently while also being as efficient as possible.  This guide is a rough estimate and variances could be caused by actual temperature, wind speed, humidity or sunlight.

Surface Area in Square Feet

  • 200
  • 400
  • 600
  • 800
  • 1000

Amount of BTU's to Increase 20F (11c)

  • 55,000  BTUs
  • 105,000  BTUs
  • 160,000  BTUs
  • 210,000  BTUs
  • 265,000  BTUs

A pool with a surface area of 450 sq ft would require a heater with approximately 130,000 BTUs of output as a minimum.  A 160,000 BTU heater with 85% efficiency (160,000 x .85 = 136,000) would be sufficient as a minimum to increase the temperature of a pool with 450 sq ft surface area by 20F.

Best Gas Pool Heaters for Salt Water Pools

Now that you have successfully worked through calculating the most efficient BTU rating for your pool you can make a more informed decision about purchasing a gas pool heater.  We've put together the top rated gas pool heaters on the market from the most reputable brand in pool heaters. 

All pool heaters manufactured today are made to withstand salt and corrosion as long as salinity levels are within recommended range.  It is important however that you keep your pool balanced including pH, chlorine and calcium hardness.  If any of these levels are out of range they can cause corrosion, scaling or calcium build up. 

If you would like some added assurance that your heater remains in top working condition we recommend using a zinc anode.  A sacrificial zinc anode will protect anything metal in your swimming pool by sacrificing itself or breaking down instead of metal hardware in your pool.  An anode will act as a piece of insurance if your pool ever gets out of balance and reaches corrosive levels. 

Another important piece that you can add to your pool system to keep your heater in good shape for many years is a check valve.  A check valve should be placed between the heater and chlorine generator in your plumbing system.  If you would like more information be sure to visit our salt water pool conversion page that has a lot of helpful information about converting and installing a healthy salt water system including a gas pool heater. 

SWPS Home Page > Inground Pool Heaters