How To Select a Gas Heater For Your Pool or Spa


  3.15 out of 5 stars on 37 ratings
(Click on a star to add your rating)

Many people buy a pool heater to extend the use of their pool by 2-3 months or to heat up their Spa 20 or 30 degrees for immediate use. This guide takes you through the many options to consider when purchasing a gas heater.

Please click here to view our How to Select an Inground Pool Heater Series.  


Step by Step


Step 1

Gas Heater vs Heat Pump - Your first question might be one of cost. One alternative to a gas heater is a heat pump that runs on electricity and uses the outside air to heat your pool or spa. The data shown at the left is based on a gas heater and a comparable heat pump in the upper range of capability. A gas heater will heat your pool in the range of five to seven times faster than a heat pump and it costs half as much as a comparable heat pump. The main issue, however, is operational cost. Depending on energy costs, a heat pump can save you up to 75% over propane gas and 40% over natural gas. If you are in the northern states, you must be aware that heat pumps are only effective when the outside temperature is above 40 degrees. Below that temperature, the heat pump switches over to electric heating coils (resistive heating) which costs more than either gas.

Please click here to view our Which Is Best: A Swimming Pool Heater or Heat Pump Blog 

Step 2

Propane vs Natural Gas - Gas heaters are manufactured to burn either of two gases: propane (LP) and natural gas (NG). Many home owners have access to NG to heat their homes, so NG being available, they would also use it to heat their pools. If you don't have NG piped to your house, you will have to buy a large LP tank and have it trucked to your house periodically. Subject to fluctuating prices, LP gas operating costs can be two and a half times the cost of NG.

Step 3

Altitude - Heaters are manufactured to operate at different altitudes. Most are set for 0 to 2000' but they are also available for operating at higher altitudes. Ranges of 2000' to 6000' and 6000' to 9000' are common options.

Step 4

Low Nox - Parts of Texas and California have emission standards for heaters. Low Nox heaters are designed to meet the Nox Emission standards set by the California South Coast Quality Air Management Commission for 2001 and the Texas Natural Resource Conservation Commission Code. Texas requirement is for commercial only, not residential.

Step 5

Durability - For longer heater life look for a cupro nickel heat exchanger and tubing vs the standard copper units. Cupro nickel holds up better in fluctuating pH levels and salt systems. Also many manufacturers are going to polymer/resin headers for superior flow performance and erosion resistance from high flow conditions. ASME requires cast iron headers for commercial applications.

Step 6

Size - The required size of a heater depends on the size of your pool or spa and how fast you want to heat up your pool. In the northern states, you will probably want the larger heaters to compensate for the colder temperatures. Above ground, pools use heaters from 55K to 130K BTUs. In-ground pools and spa general run from 100K to 400K BTU. For an average 15' x 30' pool (15,000 gallons), a 300K BTU heater would raise your pool temperature 2 degrees per hour; a 400K BTU heater, 2.7 degrees per hour. For a 20' x 30' pool (20,000 gallons) the temperature rise for 300K and 400K heaters would be 1.5 and 2 degrees respectively. By contrast, these same heaters would raise the temperature of an average size spa 30 degrees in 35 and 20 minutes respectively.

Please click here to view our Sizing Your Pool Heater Blog  

Step 7

Millivolt vs Electronic Ignition - Millivolt is the term used for a standing pilot light which stays light all the time. The other option is an electronic ignition which lights the burners with an intermittent spark like today's gas grills. This is a more efficient way to control your heaters gas usage and avoids gas leaks if the pilot goes out. The picture shows the position of the ignitor used in an electronic ignition system.

Step 8

Dual vs Single Thermostat - Some of the smaller heaters only have one thermostat to control pool temperature. Most heaters have dual thermostats for both a pool and a spa running off of the same heater,

Step 9

Force air - Some heaters, notable Hayward, have forced draft system which constantly move air through the combustion chamber at a precise flow rate. This eliminates all outside weather variables that can affect the heating performance, such as high wind conditions. Other manufacturers, like Raypak, eliminate these conditions thru their built-in wind resistant design.

Step 10

Controls - Heater controls generally vary by the size of the heaters. The smallest heaters may just have a single knob connected to a thermostat to control the heater. The larger heaters might have smart microprocessor with LCD displays and diagnostic read-outs to set and continuously monitor operating status of the heater. Picture shows the control panel for a Sta-Rite heater.

Step 11

Thermal efficiency - Most heaters have an efficiency rating of between 79-83%. This rating is related to the heat transfer from the burners through the heat exchangers to the water. For example, a 300,000 BTU heater with an efficiency rating of 83% actually transfers 249,000 BTUs when heating water. The Jandy Hi-E2 heater has one of the highest thermal efficiency rating at 95%.

Please click here to view our How Much Does it Cost to Run My Pool Heater Blog 

Step 12

Solar Blankets - Regardless of which heater you ultimately choose, invest in a solar blanket to cover your pool when it's not in use. It will keep your added heat in the pool and save you 40 to 50% in operating costs. Click here for Solar Blankets,

Please click here to view our Solar Blankets  


(1 to 10 of 10)

Anonymous  Posted: 3/22/2018 

I also have just ordered my 3rd Raypak Heater. Same issues with the rust. I had premature wear out because I did not follow instructions on adding Chlorine to the pool. I put Chlorine tablets into my skimmer. And dumped the bags of Shock down the skimmer. This new heater, I ordered a Cupro Nickel Heater. And will be keeping my Chlorine tablets in a Pool Surface Floater container. I also will be diluting my shock in a bucket totally prior to adding.

InyoPools Product Specialist  Posted: 4/25/2016 

Rusted out heater floor panel – According to a Raypak tech rep, the rusted floor panel was due to condensation which in turn was due to a failed Unitherm Governor. In Raypak’s words, “The Unitherm Governor inside the header helps reduce condensation from low inlet water temperatures. It automatically regulates the water flow to help keep the water temperature in the heat exchanger above 105°F. Both water temperature and water flow rate are controlled to eliminate condensation, sooting, and scale build-up that can shorten heater life”. The Unitherm Governor is often corroded by chlorine if the chlorine levels are allowed to exceed the normal operating limits. One way to determine if the Unitherm Governor has failed is to listen to the heater during operation. If the Governor has failed, you will hear sizzling when the water condensation drips on the heater tubes.

Anonymous  Posted: 4/18/2016 

Good article, but IMO you forgot one other aspect that I feel is important: internal rust resistance. We bought a RayPak NG heater with our pool - it worked fine for years, but after just the first year I was very unhappy to see that the internal metal cabinet parts had already begun to rust. You could just tell they weren't going to last long. Well before the heat exchanger began leaking, parts of the floor panel underneath the burner ass'y had already completely rusted out. Nothing left but piles of "rust dust". You'd think that the manufacturer would at least try to make the cabinet parts somewhat rust resistant. Here you've got metal alternately exposed to extreme heat and outside moisture. Very disappointed with that design. Won't be buying RayPak, ever again.

InyoPools Product Specialist  Posted: 3/29/2016 

Mike - Here is our link to LP to NG conversions kits. Talk with someone that has done these conversions before or read up on it. I'm told it is not hard but there is a chance of an explosion if it's not done correctly. Also check for any local code restrictions.

 Posted: 3/28/2016 

I am planning on building my own spa/hot tub. I see plenty of used pool heaters on Craig's List but they are all propane units. I have NG coming into my home. Is there a way to convert Propane to NG? Do I need to buy a different regulator?
I need to go as cheap as I can so any info you provide will be greatly appreciated.


 Posted: 9/30/2015 

I us a Raypac natural gas 055B Spa heater to heat my 5000 gallon fish pond. I live in Denver Colorado which is a mile high. The unit is protected from the elements but only lasts about three years. I have gone through my third heater.
There four major problems with the unit:
1. All of the sensors are too close to the flame and they are deteriorated over time by the heat.
2. The heat exchanger clogs up with soot and requires cleaning which is difficult, due to the construction of the unit.
3. The welds on the heat exchanger tend to leak and at that point the fins corrode.
4. A new heat exchanger costs $550, A new unit costs $750 so therefore every three years I buy a new unit.
I will be glad to entertain any suggestions.
Mike Casey


Anonymous  Posted: 6/26/2015 

Good article. It was helpful.

 Posted: 3/19/2015 

cover all the key areas in a straight forward manner. would like links to pursue specific areas of interest in more detail. Well done, thanks!

Anonymous  Posted: 6/29/2014 

Excellent article! New pool owner who knows virtually nothing of pool heaters and I am now comfortable purchasing a pool/spa heater thanks to this article!

Anonymous  Posted: 6/18/2014 

Excellent article. Very informative and helpful