Is my heater working correctly?

EskimoPie

LifeTime Supporter
Jul 27, 2007
278
Sahuarita, AZ
#1
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
#2
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
#3
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
#4
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
#6
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.