1. ## Heating pool

My daughter is having a birthday party on March 2nd and wants to heat the pool. I am trying to figure out how long I will need to heat it to get to temperature. I am thinking a water temp of 85 should be warm enough for kids. I am located in Houston, TX so there is no telling what the weather will be like in early March. Could be 90 outside or 40. Currently our water temp is 61 degrees. Pool is roughly 18,500 gallons and my heater is a Jandy LT400N-L and is rated at 399,000 btu / hr. Is there a formula for me to determine how long it will take to heat my water?

2. ## Re: Heating pool

It takes 1 BTU to heat 1 pound of water 1 degree, you have 18500 gallons of water at 8.35 lbs per gallon (154475 lbs). So your heater will heat the pool 2.58 degrees an hour, assuming 100% effeciency. Or, about 7.75 hours to raise the pool 20 degrees, but I would assume a lower effeciency. Since my memory might not have this completely, correct, maybe someone will drop by and give you a more accurate calc, if necessary.

3. ## Re: Heating pool

Thats pretty close. I got 9 hours for a 24 degree rise.

18,500 x 8.33 = 154105 x 24=3698520/ 400, 000= 9.2 hours.

Assuming the heater is 85% efficient, it will take roughly 11 hours. At 4 therms per hour, thats 36 therms at ~\$1.00 per therm, (unless your gas prices are pretty high), thats about \$35-40 to heat it up. Not bad really.

4. ## Heating pool

1 BTU = energy to heat 1 lb water by 1 degree F. Assume 90% efficiency for heater, then your 400,000 BTU heater can heat 360,000 lbs of water by 1 degree per hour. 18,500 gal pool x 8.34 lbs per gallon for water = 154000 lbs water. So I would estimate around 2 degrees per hour ignoring any solar gain or heat loss from wind.

A solar blanket/cover would be highly recommended.

Depending on how your gas is priced (either therms or Mcf) - around 1000 BTU per cubic foot or gas. 100 cf in a therm and 1000 cf in Mcf. Gas in Dallas is around 4.50 per Mcf - 400,000 BTU heater burns 400 cf per hour or .4 Mcf so around 2 bucks per our or a dollar per degree!

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5. ## Heating pool

I guess we were all typing at the same time!

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6. ## Re: Heating pool

@brownchristian - It will depend on the weather. I live SW of Houston and I can tell you to just to heat my 10+K pool it is about 40 bucks on average. However the real factor will be the weather and wind. Hot and humid and no wind it will be easy to heat up. Cool and windy it will take a long time. I can heat my pool about 4 degrees per hour until I get close to the outside temp after that it takes a long time.

7. ## Re: Heating pool

One tip... heat the water to temp a day early, cover it if you have one, and check your chemicals a couple of times after it heats up. Thing change when you pump that much heat in.

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