The Ultimate Guide to Understanding How Pool Heaters Work

What Do Swimming Pool Heaters Do?

To keep it simple, both natural gas heaters and electric heat pumps will give you the same end result: warmer water.  They operate a bit differently.  A Natural gas heater uses gas while a heat pump uses both electricity and the outside air to function to give us our desired temperature.  As the swimming pool water is drawn from your skimmer and/or main drain, the pool pump pushes the water through your various pieces of equipment.  You definitely have a swimming pool filter as this is where the water gets cleaned.  You may also have a salt system, in-line chlorinator and, you guessed it, a heater.  The warm water is then returned back into the swimming pool through the return inlets. To see how heaters are sized, check it out here 

Sizing a swimming pool heater involves determining the appropriate heating capacity or output needed to effectively heat the pool water based on several factors, including the pool's volume, desired temperature rise, climate, and other variables. 


So you are thinking of purchasing a heater.  Maybe yours cannot be repaired.  Maybe you want a more efficient piece of equipment.  Maybe you want to extend your swimming season.  Maybe you are building a new pool.  Whatever the reason, you may be wondering which type of heater is right for you.  We are here to help.  There are two major types of heaters.  Gas heaters (either propane or natural gas) and electric heat pumps.  For the sake of this article we will be talking about natural gas and electric heat pumps.  Just keep in mind propane gas is an option, although not very popular except maybe in rural areas.  

Natural Gas Heaters

Natural gas heaters work in all types of climates.  They utilize natural gas to heat the water and do not rely on the outside temperature.  You will either need to have existing gas lines or have gas lines installed to accommodate a natural gas heater.  If you are looking for a quick way to heat your swimming pool or spa then a natural gas heater may be for you as they heat more quickly than a heat pump.  They are more efficient in this regard.

Pro Tip:  The size of the heater you purchase is limited to the size of your gas line as well as how long the gas line run is.

How quickly do they heat?  This depends on many factors such as the temperature of the water and how many degrees you want to heat it.  It also depends on the size of your body of water.  This is measured in gallons.  When we talk about heater “size” we are typically not talking about the footprint, or dimensions of the heater, but the heat output.  This is measured in British Thermal Units (BTUs).  Dimensions are also important.  Especially if you have limited space on your equipment pad.  The larger the heater (the higher the BTU), the more quickly you can expect your water to be heated.

Natural gas heaters nowadays come in what is known as a LoNox model.  This makes for a more efficient machine.  They come in a variety of brands and BTUs.  They can also be more affordable than an electric heat pump to purchase.  It all depends on where you shop.

Pro Tip:  Always go with the largest BTU your gas lines can accommodate.  While pricier up front, you will get that money back as you save on operating costs.

Electric Heat Pumps

Electric heat pumps are good for climates that do not drop below 45-50 degrees Fahrenheit. This is because they rely on the outside air to heat your water.  Swimming pool heat pumps run on electricity–not gas.  They tend to have a lower operating cost annually versus a natural gas heater.  They will tend to last longer as well!  They are efficient and friendly for the environment.  

Heat pumps function by extracting the outside air and utilize a compressor to increase the heat of the water as it passes through.  Typically, 3-5 degrees Farenheit each time.  Heat pumps are not designed for quick heating.  In fact, you can expect to run your heat pump 24-72 hours to get to your desired temperature.  Like a natural gas heater, this depends on gallons, current temperature, desired temperature, BTUs and with a heat pump, the outside temperature.  

Heat pumps are used to maintain your water’s temperature.  That is why they need to run for so long.  They are also measured in BTUs.  They are also slower at increasing the water’s temperature.  Heat pump usage is measured in watts or kilowatts.  You can check out your electric bill to see your price per watt/kilowatt.

Pro Tip:  If you have solar on your home, a heat pump is a great investment for you.  It can actually earn you money if your power is purchased back by your utility company.

If a Heat Pump is Right for You

Heaters are expensive.  That is because of all the fun you will have if you want to put a positive spin on things.  I am a positive type of gal.  If you were to go to your local swimming pool supply store either a gas or electric heater of a good size will run in excess of $4,000.  Heat pumps tend to work a bit higher.  I recommend going with a name brand and efficient heater.

You can actually get a name brand heat pump for MUCH lower than you might think.  The Nationally known, ComforTemp, makes an efficient high quality electric heat pump.  When I say quality, I mean amazing quality!  They are fast acting and energy saving.  They also make less noise.  The best part, in my opinion, is the fact that they self diagnose themselves for easy maintenance.  Why sacrifice quality for price, I say!  You can have both.  Check them out here.  See you poolside!