# Thread: Estimation of a heat cost

1. ## Estimation of a heat cost

Hi all,

I have just had a new heater put in for my indoor pool.

This pool is 20,000 gallons and the new heater is the Rheem 266,000 BTU electronic ignition with cupro- nickle exchanger.

I was wondering what the initial gas costs were to increase the water to a comfortable level? and then the gas costs to maintain that comfortable level?

I suspect the initial cost would obviously be higher and I hope the cost to maintain that level should be a bit lower.

I am in Chicago, IL, and I suspect the heater shouldn't run too much in the summer - hoping the warm weather keeps the water warm. I also do have the blue solar cover - but not sure if that blue cover is designed to retain the heat in the pool?

Any tips to keep operating costs lower would be fantastic.

Thanks

2. ## Re: Estimation of a heat cost

Calculation of the required BTU to raise the temperature is pretty straight forward ignoring environmental losses which should be less indoors. I am not sure how to calculate maintaining the temp.

What is your cost of gas?
And how many degrees does the pool need to go up?

Posted from my Droid with Tapatalk ... sorry if my response is short

3. ## Re: Estimation of a heat cost

When we were heating the pool continuously in the spring and fall we were spending almost \$200/month. Doing the same mid-summer was much less. My pool is a little bit smaller and I live well South of you.

Any kind of cover will help a great deal in retaining heat. Most heat loss is from evaporation and a cover prevents nearly all evaporation.

4. ## Re: Estimation of a heat cost

Originally Posted by jblizzle
Calculation of the required BTU to raise the temperature is pretty straight forward ignoring environmental losses which should be less indoors. I am not sure how to calculate maintaining the temp.

What is your cost of gas?
And how many degrees does the pool need to go up?

Posted from my Droid with Tapatalk ... sorry if my response is short
It is currently in around 57
We will want it at around 88

Gas Cost is - Therms x \$0.42 (looking at my last regular gas bill)

Once it hits the level around 88, I suspect the heater will go on and off to just maintain that temperature. I will also use a blue solar blanket to keep in heat when not in use.

Hopefully in the summer the water just stays warm a bit better - even though it is an indoor pool - I am hoping the summer will help in some way...

5. ## Re: Estimation of a heat cost

20,000 gallons is about 165,000 lbs.
Temperature increase is 31.
1 BTU will raise one pound of water one degree Fahrenheit
31*165,000 = 5,115,000 BTUs
I them = 100,000 BTU. Therefore 51.15 therms.
51.15*\$.42 = \$21.48 to heat just the water initially.

You will also be heating the concrete shell, and the air above the pool, and of course the pump and filter will get heated to 88 as well, and will lose heat. Plus the heater will not be 100% efficient. Just from my own experience, you'll probably lose half. So figure something more than forty bucks just to heat it initially.

I recall from physics class a long, long time ago that the rate of heat transfer depends a lot on the difference in temperature, but I forget the equation. I'm sure I just remembered it long enough to pass the test. It won't be cheap.

Those plastic bubblewrap covers will retain an awful lot of heat, definitely use one.

6. ## Re: Estimation of a heat cost

Well, I typed it, so here it is even though it is now repetitive:

1 BTU will raise 1 lb of water by 1 degree F

20,000 gal * 8.3 lb/gal = 166000 lbs

166000 lbs * 31 degs = 5,146,000 BTUs needed

Assuming 85% efficiency, you heater will supply 266,000 BTU *.85 = 226,100 BTUs/hr of heat
So it will take 5146000/226100 = 22.75 hours to raise the pool by 31 degrees

Again assuming 85% efficiency, your heater will use 5146000/.85 = 6,054,000 BTUs for the initial heating
1 therm ~= 100,000 BTUs, so you will need 60.54 therms * \$0.42 = \$25.43 for the initial heating

BUT, these calculations ignore the heat lost to the environment, so they are a little optimistic.

Once you are just trying to maintain the temp, you will have to overcome these environmental losses which are hard to estimate.

7. ## Re: Estimation of a heat cost

thanks for your help everyone, helps a lot to use these calcs for future references.

@Richard you seriously look like Walter White from Breaking Bad...

8. ## Re: Estimation of a heat cost

sorry guys it seems the pool is 30,000 gallons, can i get an estimation please?

9. ## Re: Estimation of a heat cost

Multiply everything by 1.5

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10. ## Re: Estimation of a heat cost

thanks! will do turns out the temp was around 46 when it started and after 18 hours its gone from about 46 to about 66 in temp (20 increase in 18 hours).

Is this normal?

11. ## Re: Estimation of a heat cost

Originally Posted by pred8er
thanks! will do turns out the temp was around 46 when it started and after 18 hours its gone from about 46 to about 66 in temp (20 increase in 18 hours).

Is this normal?
Hmmmm, let's see...

30,000 gallons is about 247,500 lbs of water.
247500 * 20 = 4,950,000 btu.
Heater is 266,000 btu/hr
In a perfect world, that would take 4,950,000/ 266,000 = 18.6 hours. So I'd say you're doing really good! Either the pool is smaller than you think, the heater is bigger than you think, or the thermometer is off a little, because I can't imagine anything being that efficient.

12. ## Re: Estimation of a heat cost

perhaps the pool could be smaller, its between 20-30k gallons. Its hard to get something accurate i think since the pool is not rectangular but curvy

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