Pool heating

Evilgrimace

Member
Nov 17, 2016
8
Bradenton, Fl
We live in SW Florida and we have a 15K gallon 15' x 30' AG pool with 2' sub grade leaving about 18" of water above grade. We just installed a gas heater and now wonder about best operating practices...we have a solar cover installed when we're not in the pool...question I'm asking myself now is do you leave the heater off until you anticipate using it or do you heat it a bit all time time and heat it to the desired temp just prior to use? I'd imagine someone has done the math and I realize it's ambient temperature dependent...
 

Nectarologist

Well-known member
Apr 3, 2015
580
New York
You'll get answers on both sides of the fence. I think it comes down to how you use your pool. With the solar cover you are doing the #1 thing to keep costs down regardless of how you heat. I keep my pool at 84 and turn it up to 86 if it's cloudy when we're swimming. If I know I won't be using it for an extended period of time (vacation or several days of rain) I will turn it off. I don't know that it make too large a difference either way but I would keep it heated this way it's warm when you want to get it. I am not aware of any scientific data on this.
 

xyz

Gold Supporter
Sep 8, 2016
641
Escondido/CA
You can get some pretty good rules of thumb if you take some measurements. You will need

1) cost to heat your pool 1 degree
2) speed your pool cools normally
3) speed your heater heats your pool 1 degree.

I -think- with this info you can decide what makes sense.
 

Evilgrimace

Member
Nov 17, 2016
8
Bradenton, Fl
Thanks gents, I am missing the cooling rate of our pool. Had the LP connected this past Tue...I have data on theoretical heating time (using two methods of calculating I've come up with 2.3 degrees per hour to 3 degrees per hour) and my cost is roughly $8 per hour at my fixed rate gas cost...
 

xyz

Gold Supporter
Sep 8, 2016
641
Escondido/CA
OK, so cooling rate will be temp dependent but that one is easy. Leave the heat off, and take a few temperature measurements during a 24 hour period. Without clouds at night will give you the worst-case heat loss, especially if it is windy.

Also, another question I forgot to ask is, what would your pool temp be if you were not heating at all?
 

Swampwoman

TFP Expert
LifeTime Supporter
Apr 27, 2012
3,835
Grand Rapids, MI
This doesn't directly answer your question bu seems to b a highly accurate calculator for heating costs: SWIMMING POOL ENERGY TEMPERATURE CALCULATOR | Neil Anderson

At about $2.65 per degree (if you get 3 degrees an hour) it will depend how many days between uses I suspect.

Here, in Michigan with a cover on and even freezing temps but inside a dome, I'm not losing much more than 5 degrees a day or less right now over a 14 hr period with heater off. (My nat gas is only .70 per CCF so about $1.50 per degree.)

So for me to swim daily its $7.50 at the moment. BUT I heat it to 94 for 5-6 hrs and then turn heater off, without Thermostatting, which is IMHO cheaper at least in these kind of extremes.

If I let it drop to 40 from 94 over a few days, (degree differential of air to water, times surface area of pool, x 5 btu into volume of your btu to equal 1 degree for your water...eg in my case, one degree in 24k is worth about 200,000 btu) ...

It would take me at least 54 hours at 1.50 to get back up to temp IF my 266k btu heater could stay at 1 degree an hour (depends on differential). So that's $82...or more than ten days of heat ;) Make sense?
 

Evilgrimace

Member
Nov 17, 2016
8
Bradenton, Fl
Uh dang! You've got that down don't ya? Good info! Thx.

We we turned the heater off Sat at noon...water was 90, overnight low was 60, morning pool temp was 82, last nights low was 60 and water was 80 this morning. Continuing to collect data!
 

Swampwoman

TFP Expert
LifeTime Supporter
Apr 27, 2012
3,835
Grand Rapids, MI
If you tell me
A) how many gallons
B) square footage of pool surface
C) if you're using cover at all times when not swimming
And
D) the BTU output of your heater I can show you some rough calculations after wrk or when I get a break ;)
 

Evilgrimace

Member
Nov 17, 2016
8
Bradenton, Fl
It's a 15x30 above ground pool. It holds 15,000 gallons and that's about 450 sq ft, cover is in place when the pool isn't in use and we have a heater that claims to be 400,000 btu...thanks for your opinions and calculations
 

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Swampwoman

TFP Expert
LifeTime Supporter
Apr 27, 2012
3,835
Grand Rapids, MI
So if the air to water differential is about 20 degrees, you'd lose about 45,000 BTU an hour which in a 15k gallon pool should be roughly a third of a degree, assuming you get about 2.6-3 degrees an hour from your heater. So to keep heat at 85 would take an hour of running for every 9 hours the heater isn't running.

I bet with a solar cover your loss would be less.

With an above ground, I can't calculate the impact of conductive loss, so this is all just wild-arsed guessing on my part, but with a powerful 400 btu heater and a solar cover, I'd say just crank up the heat right before use and don't bother Thermostatting for your cheapest date ;)
 

xyz

Gold Supporter
Sep 8, 2016
641
Escondido/CA
That makes sense with those numbers.

Basically, if you lose heat quickly, and can gain it quickly, less energy is lost, and if you can heat quickly, as you can, the only benefit ti keeping it warm is you don't have to wait to go in.

Also, if put your pool information in your signature, it helps everyone help you better.
 
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