Is my heater working correctly?

EskimoPie

LifeTime Supporter
Jul 27, 2007
278
Sahuarita, AZ
We had a warm spell over the weekend down here in Tucson so I fired up the gas heater to go swimming. The pool water was ~48 degrees prior to turning on the heater and I started the heater going at ~6:00AM (granted it was probably in the mid 40's that early in the morning). It's a new Sta-Rite 400k BTU heater and it would only raise the water temp by about 3 degrees per hour. It took until about 4:00 in the afternoon to reach 80 degrees. This is the first time I've tried to heat the pool from so cold to so warm and I was honestly expecting a 400k BTU heater to do it quicker than that. Am I expecting too much?
 

Exchemist

Well-known member
Oct 5, 2007
86
Philadelphia, PA
We can do a quick calculation. A British Thermal Unit (BTU) is the amount of heat energy needed to raise the temperature of one pound of water by one degree F. Your heater is 400,000 BTU/hour. So, it should raise the temperature of 133,333 pounds of water 3 degrees F in one hour. 133,333 pounds of water is 16,667 gal. I don't see the size of your pool, but this seems like a reasonable size for a pool.
 

Exchemist

Well-known member
Oct 5, 2007
86
Philadelphia, PA
Now I see in your signature that you have a 12,000 gal pool. (Signatures don't show when your composing a reply.)

3 F/hour for 12,000 gal is 288,000 BTU/hour. I suspect the 400,000 BTU/hour is the heat output of the burner. This would mean that 72% of that heat is getting into the pool water, which is a reasonable efficiency for a gas heater.
 

mnormington

LifeTime Supporter
Jan 23, 2008
109
Burbank, IL
I just have to chime in here. It never fails to amaze me the amount of smarts and expertise present on this board. I have taken a lot from this board and I don't think I'll ever be able to give back as much. I mean, I've always considered myself a reasonably intelligent person, but some of you guys on here make me feel like a kindergartener. What a trip! This thing is a fun read. Thanks for the chuckle Exchemist.
 

EskimoPie

LifeTime Supporter
Jul 27, 2007
278
Sahuarita, AZ
hehe, thanks Exchemist... I'm an aerospace engineer and didn't even think about just doing the math... not to mention I hated thermodynamics! :) I suppose a 72% total efficiency does sound pretty good considering the losses in the heater itself, the pipes in the ground, and heat loss to the atmosphere on a chilly morning.