Help with heater size -- is smaller than recommended still Ok?

kfinke

Member
Aug 28, 2017
21
Cincinnati,OH
I have a 32500 gal pool, 20x40 (800 sq. ft.). Most pool heater sizing charts would recommend a 300-400KBTU heater, even adding in the quip that bigger is better.

However, the previous owners of the house had a pool heater. It died, and they removed it. Gas line and electric are already there. However, they installed a 3/4" gas pipe. With a run of over 80 feet, we've calculated that the best we could do would be about a 200,000BTU heater. We have a solar blanket, and I would be quite diligent about keeping it on when the heater is running. I've been told that a BTU of heat added to the pool is a BTU of heat added to the pool. If that is true, and the blanket will keep most of the heat in, then is it a true statement that the only disadvantage to a smaller heater would be that it would take twice as long to raise the pool by X degrees than a 400K unit? It would also be a true statement that both the 200K and the 400K would burn the same amount of gas to raise the pool by that X degrees?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
5,423
Northern NJ
Yes & sort of yes

I think a larger heater may be a bit more efficient then a smaller heater running longer. But not enough to make a big difference.
 

kfinke

Member
Aug 28, 2017
21
Cincinnati,OH
Don't overthink it. Go 400k BTU heater. Bigger is better. Quicker to get to desired heat temp.
Thanks for the replies, but perhaps I didn't make the problem clear. My current gas plumbing can only supply a 200K BTU unit. To do 400K, I will need to replace 40' black iron pipe in the basement as well as dig up 40 feet of yard to install 1 1/4" pipe instead of 3/4". The other choice would be to convert to a high pressure gas service, adding regulators at all gas appliances. Neither sound cheap.
 

thegreenblade

Well-known member
Jul 14, 2017
45
Chicago IL
I have a 250,000 BTU heater for 14,900 gallon pool the water temperature the other day was 52 took over 12 hours to get it in the 80s I have an inch and a quarter pipe ,yellow buried then reduce down to 3/4. I would do it right the first time, bigger is better. I also have a dome on it.
 

smracing

Well-known member
Jun 1, 2011
187
Carlsbad, NM
I had a 400k heater that died. I replaced it with a 125k. I use the heater mostly for the spa, also to extend the swimming season. I have been happy with the decision.
 

Other Threads of Interest