# Thread: How much to heat my pool - please double check this math?

1. ## How much to heat my pool - please double check this math?

Hi,
I am trying to figure out how much it will cost to heat my pool for a weekend, to get a ballpark estimate. I have a gas heater (Purex Triton Minimax 250) and trying to see how much I am in for before firing it up. Here is my data:

pool size = 15' x 30'. Water temp = 70, would like to have it 90. From this website it says I need approx 108,000 BTU's to raise the water temp. 20 degrees for this pool:

http://www.swimuniversity.com/pool-heat ... eater.html

I assume this means it takes 108,000 BTU's to get the temp up 20 degrees, at that point the heater turns off (and the pool starts to cool

From the below website it says there are 1080 BTU's per cubic foot of gas:
http://www.appleheating.com/heating/fue ... calculator

This gives a requirement of 100 CCF.

In my area gas prices are running about \$0.7 / CCF from below:

http://www.centerpointenergy.com/servic ... prices/HO/

That would be a total of 100 * 0.7 = \$70, to heat my pool by 20 degrees. Or to raise it 10 degrees, \$35.

1. Does this seem legitimate? Am I missing any basic steps here?

2. Once pool is at 90, how much does it cost to maintain this temp for 8 hrs, or for 24 hrs?

3. My heater is rated for 250,000 BTU's per hour. How can I determine how long it would take to raise the temperature of the water - eg. 1 hour, 8 hrs, etc?

Thanks for any help you can provide. My next step is to research solar blankets

2. ## Re: How much to heat my pool - please double check this math

It takes huge amounts of energy to heat a pool. 1 btu raises 1 lb of h20 1 degree. 1 gallon is 8.34lbs, you have about 83,000 lbs of h20 to heat. If you want a 20 degree rise in temps that would be about 1,700,000 btu's. Gas heater's run about 80% efficient.

You would use about 20 therms in 8 hours to heat your pool to 90. What do you pay a therm (100,000 btu's)?

With a solar blanket you might loose 5 degrees or so depending on average ambient temp. Without the solar blanket it would be Like trying to heat the house with no roof.

FYI with a properly sized solar panel unit you can keep your temps about 20 degree above average ambient air temp. It would help you to use much less gas if you have sunny spring/falls.

My water will be near 90 this weekend. One of the benefits of a smaller pool.

Edit: it looks like your calculations are close. There are about 92 ccf to a therm. I guess we all get to pay for energy one way or another. My electric rates top out at 0.30 a kWH but gas is about \$1.25 a therm. I would like a gas fired hot tub rather than my electric.

3. ## Re: How much to heat my pool - please double check this math

I'll ball park you some figures. California. PG@E. Graduated scale for therms (\$0.96476/therm, baseline) , 20000 gallon pool. Heating it 24/7 to 82 degrees, no cover, all season. About 250-300 dollars a month for natural gas alone, May to September. I suspect your cost would be much less, even going to 90, since it is only one weekend.

4. ## Re: How much to heat my pool - please double check this math

Thanks, that is a great ballpark estimate. My pool is 1/2 the size so maybe \$150/month to run it 24/7 w/o cover. Thanks for the info!!

5. ## Re: How much to heat my pool - please double check this math

8.34 BTUs to heat one gallon of water 1 degree
10000 X 8.34=83,400 BTUs to raise your pool 1 degree
10 degrees rise = 834,000 BTUs

1080 BTUs per cubic foot X 80% efficiency of heater = 864 BTUs
834,000 BTUs divided by 864 BTUs = 965.278 cubic feet of gas

There's variables involved such as air temp, wind, actual weight of water as it heats up, cover or no cover etc. The biggest variable is an insulating cover. Heating a pool with no cover would greatly add to the cost.

Edited for confusion over price for natural gas

6. ## Re: How much to heat my pool - please double check this math

I heated my 22000 gallon pool with natural gas for one day this spring from 72 to 82 and it cost me \$150. I watched the meter the entire time rather than estimating. For an entire weekend, from 70 to 90, it also depends on the weather and cover. Make sure you keep the thermal cover on. Get ready to dish out \$300 (and that's a wild guess)

7. ## Re: How much to heat my pool - please double check this math

Perhaps you've already ruled it out due to personal preference, but I'd only go to about 85 degrees. 90 is too warm for me. That should help somewhat if cost is an issue. Also, are you sure that the pool is at 70 degrees? I'm in Houston as well and my pool is 20 x 20 (but only avg. 4 feet deep) and it was at 80 on Wed (10/5) afternoon even after the recent "cool" spell. I've only used my heater once for the pool (but several times for the spa) and I've never really noticed a significant increase in my natural gas bill.

8. ## Re: How much to heat my pool - please double check this math

I can tell you that using your heater for your pool and using it for your hot tub is a big difference. I heated my hot tub at 70 degrees full-time last year (plaster with insulated hot tub cover) and only heated to 100 when in use and it averaged about \$70 / month throughout the entire winter. Our winters in MD went into the 0-32 degree F many days during the winter also. I think the one month where it was coldest, we spent about \$100 for that month. Now, heating my pool from 72 to 82 in one full-time heating day cost me about \$150 just for the day and it was about 70 degrees outside. It also included the few times I heated the hot tub also during that month. There are many factors and outside temperature is certainly a big one. My gas costs during the entire summer which included heating the hot tub 2-6 times per month have averaged about \$20/month and that includes a \$5 delivery charge each month.

9. ## Re: How much to heat my pool - please double check this math

Another comment - The best thing about gas - you can take a reading before you begin heating the pool and then take readings periodically and determine how much it is going to cost. After running it 24 hours, I was happy to turn the heater off for the one time I did it. I know my sister ran her propane tank dry after one weekend when her pool was new. Very quick lesson. The other problem I run into is if I forget to turn off the heater during the pool season and I switch all of the plumbing back to full circulation, it is heating the entire pool - caught myself a couple of times after about an hour of continuous heating.

10. ## Re: How much to heat my pool - please double check this math

Xs, that's good to know and it makes sense. This weekend may be the last weekend I can use my pool without the heater and I would not be inclined to spend \$150+ per day to heat it.

It's supposed to be around 88 for a high on Sat and 86 on Sun with lows in the low 70s--but warmer in the city, so my pool probably will be in the 82 degree range which is fine with me.

11. ## Re: How much to heat my pool - please double check this math

My pool is approximately 10K gallons and I can raise my water temp 3 to 4 degrees per hour. Using a 400K BTU heater. I did the math this spring when it started warming up and I think I figured it cost me about 30 to 40 bucks to heat it 20 degrees from 65 to 85. Outside temps were in the mid 80's at that point. Basically my heater used 4 CCF of natural gas per hour costing me about 1 dollar per CCF or 4 dollars per hour to run the heater.

12. ## Re: How much to heat my pool - please double check this math

You're underestimating. You forget how much heat you'll lose to warming up the concrete and the dirt around the pipes. And evaporation. I heated my pool up for the housewarming party. Cost me over \$100. And then the weather changed and it was grey and windy and no one went in anyway.

13. ## Re: How much to heat my pool - please double check this math

This post shows the cost for gas heating my 16,000 gallon pool to extend the season, but I have solar panels and a mostly opaque safety cover (thinner than bubble-type covers). Late fall and winter get prohibitively expensive since the sun is low so solar doesn't help and the air temp is cold so heat loss is greater. So we don't bother to heat the pool in December through March and it's generally too cold in air temps anyway.

14. ## Re: How much to heat my pool - please double check this math

Originally Posted by XsAllOverIt
I heated my 22000 gallon pool with natural gas for one day this spring from 72 to 82 and it cost me \$150. I watched the meter the entire time rather than estimating. For an entire weekend, from 70 to 90, it also depends on the weather and cover. Make sure you keep the thermal cover on. Get ready to dish out \$300 (and that's a wild guess)
Dear lord, how much does your NG cost per therm?

For 22,000 gallons to heat up 10 degrees with a 400k heater should take about 4 hours. At ~4 therms per hour, that roughly 16 therms. Cost per therm is around \$1.18, at least in my area. That 10 degrees here would cost ~\$19.00. Even with propane at \$3.00 a gallon, its less than \$50 bucks. Are you sure you did the math right?

15. ## Re: How much to heat my pool - please double check this math

Originally Posted by bk406
Originally Posted by XsAllOverIt
I heated my 22000 gallon pool with natural gas for one day this spring from 72 to 82 and it cost me \$150. I watched the meter the entire time rather than estimating. For an entire weekend, from 70 to 90, it also depends on the weather and cover. Make sure you keep the thermal cover on. Get ready to dish out \$300 (and that's a wild guess)
Dear lord, how much does your NG cost per therm?

For 22,000 gallons to heat up 10 degrees with a 400k heater should take about 4 hours. At ~4 therms per hour, that roughly 16 therms. Cost per therm is around \$1.18, at least in my area. That 10 degrees here would cost ~\$19.00. Even with propane at \$3.00 a gallon, its less than \$50 bucks. Are you sure you did the math right?
I just quoted what my BG&E bill was. Here was the actual bill. I heated the pool for an entire 24~36 hours from what I remember. The average temperature that that time was 70 degrees.

BGE Gas Delivery Service \$45.92
BGE Gas Commodity \$78.41

113 units used x 1.125(Pressure Factor) x 1.019 (Therm factor) = 129 therms used
Gas Delivery Service

EmPower Md Charge 129 therms x 0.00490000 = .63
Distribution Charge 129 therms x 0.24630000 = 31.77
Franchise Tax 129 therms x 0.00402000 = .52
\$45.92

BGE Gas Commodity
Gas Commodity 129 therms x 0.60780000 = \$78.41

Hope that helps...

16. ## Re: How much to heat my pool - please double check this math

Originally Posted by Flippy
My pool is approximately 10K gallons and I can raise my water temp 3 to 4 degrees per hour. Using a 400K BTU heater. I did the math this spring when it started warming up and I think I figured it cost me about 30 to 40 bucks to heat it 20 degrees from 65 to 85. Outside temps were in the mid 80's at that point. Basically my heater used 4 CCF of natural gas per hour costing me about 1 dollar per CCF or 4 dollars per hour to run the heater.
Whenever Lana asks to heat the pool for guests, I just say, it's coming out of your savings. We never heat our pool. We sit in the HOT hot tub and look at the pool. If anyone wants to jump in the 65 degree pool, they have a hot tub to jump back into.

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