Heater working but not heating

cooper · May 21, 2008

I recently got a free Laars Lite 2 propane heater from a friend of mine and had my PB plumb it to my system when they installed a new filter for me. It's 125,000 btu's which I know is undersized for my 24,000 gal IGP but I figured it was free and I'd only use it occasionally to boost the temp of the pool 10-15 degrees on weekends such as the upcoming holiday weekend.

Long story short. I fire up the heater the other day to see if it works and sure enough, it lites and appears to be doing it's thing. However, when I stick my hand in the pool by the returns the water feels like it's coming out the same temp as the surrounding water. I let it run for a good 20 minutes but no change.

Stupid question #1: Shouldn't the water feel warmer if not hot?
Stupid question #2: Is the heater way undersized and therefore useless and I should get rid of it?
Stupid question #3: Did I not wait long enough for the water to cycle through and become warm?

I think the water might be flowing through the heater too fast to heat up. If thats the case how do I slow it down?

Thanks in advance. You guys are a great help.

JohnT · May 21, 2008

You can't flow water too fast through a heater. The net heat flow into the pool will be the same if you heat a gallon by 1 degree or 10 gallons by 0.1 degree.

Measure your pool water temperature. Put your vacuum hose against a return and fill a bucket with the water from the return and check that temp.

JasonLion · May 21, 2008

The temperature increase can be quite small going through the heater. Even a one degree increase, which you couldn't feel, will heat significantly if you have a good flow rate. A typical heater will raise the water temperature by anywhere from one to fifteen degrees, depending on the size of the heater and the flow rate. Higher flow rates, and thus lower temperature increases, are actually slightly more efficient.

billyjoeraybob · May 21, 2008

I have a 250K BTU natural gas heater and when mine is running you can definitely feel warm water coming out of the returns. Might be because mine is twice the BTU's.

Denali · May 21, 2008

Laars heaters have an internal bypass valve that adjusts depending on flow rate. Some pool water bypasses the heater and mixes with heated water so the water coming through your return lines won't feel hot.

If the pool temperature doesn't go up at all, the bypass valve can be adjusted to increase temperature rise.

EskimoPie · May 21, 2008

I have a 400k BTU heater and my 12,000 gallon pool heats by about 3 degrees an hour when the heater is running. Your pool is twice as large and your heater has 30% of the output. That means (using my highly complex math) I'd expect about 0.5 degrees per hour with your setup. Have you let it run for a long time and have you seen any appreciable temp change long term? Obviously this depends a lot on environmental conditions, but it should give you a WAG of what to expect.

jjdurrant · May 21, 2008

I also have a 250k BTU heater and can easily feel warm water at the returns when the heater is running.

randytsuch · May 21, 2008

From wikipedia
A BTU is defined as the amount of heat required to raise the temperature of one pound of liquid water by one degree Fahrenheit

From answers.com
1 gallon of water = 8.345 lbs, so 24,000 gal = 200,287 lbs of water

So, a 125,000 btu heater will heat a 24,000 gal pool at a rate of
0.624 degrees/hr

I would round off to 1/2 degree/hr.

Could just try running it for a day, and see if you get a few degrees rise.

Randy

cooper · May 21, 2008

randytsuch said:
I would round off to 1/2 degree/hr.

Could just try running it for a day, and see if you get a few degrees rise.

Randy

I think that's what I'll do. If it's insanely inefficient (which it may be) I'll just scrap it. Like I said, it was free anyway. At least now my system is plumbed for a heater so when I eventually save up for a heat pump it will be an easy install.

Anyway, thanks for all the replies.