What size heater?


Active member
Jul 13, 2015
Southeast Michigan
I have a 24’ round pool in Michigan. We’re looking to get a heater and are between the Raypak 156 and 206. I don’t plan on running it constantly, just a few hours on the mornings I know we will swim and water is cold. Does anyone have experience with either? Obviously the 206 is a more expensive heater but is one more expensive to run (does one cost more than the other to raise the temp x degrees)? Thank you!!!


TFP Guide
Jun 4, 2012
western NY
Cost to run a heater is based on the fuel cost per BTU and the BTU load of the pool. A BTU is the energy used to raise 1lb of water 1 deg (f). If you have a 80,000 lb pool and a 100,000 BTU heater (80% efficient is normal) you should see about a 2 deg rise in temp per hour. Assuming a cost of nat gas at $1.00/therm (100,000 BTU) it will cost about $1.00/hr to run the heater and raise the water temp 2deg/hr. If I did my math correctly in my head, I am figuring your pool to come in around 110,000 lbs. The 206 is about a 165,000 BTU output heater so you would see about 1.5 deg of temp rise/hr times whatever the cost per therm is for your area. Keep in mind there are several factors that affect the ability of a heater to heat a pool, including but not limited to the ambient air temp, wind, etc.



LifeTime Supporter
Jul 4, 2012
Chicago, IL
I have the raypak 406a - raypaks get a lot of love around here. I am sure there are some nuances I am glossing over, but generally speaking it will cost you the same amount of money to raise your pool temp 1 degree whether your heater is 100K BTU or 200K BTU. The difference is in the time it takes.

I use my heater in the same way you plan to, which I would describe as wanting heat on demand. Given that, get the largest heater you can afford as they increased cost is not that high, i.e. a 400K BTU heater is not double the cost of a 200K.

I get about a 2 deg temp increase per hour during summer months and that works well for the turning it on in the AM on days you want to swim, so I would suggest the 206a based on Dan's calcs of 1.5 degree/hour. You might even consider the next largest size to get to that 2 degree/hour increase.

By the way, your sig says 21' pool, but your post says 24'. Can you clarify which is correct?
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