Heating swimming pool - could you share your experience

Hi,
I live in Toronto, Canada and would like this year to heat my swimming pool.I'll buy solar blanket to keep heat in. But I still have a question - is it better to put thermostat on set temperature and leave it like that for whole summer, or it is better to turn heating off for night? Will I use more gas to keep constant temperature? What temperature would you recommend to keep pool at?
Thanks
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PoolGuy wrote:

There would be little or nothing to gain by turning it off at night, and you may loose function as you would need a larger heater if it was only allowed to function during the day. (I am assuming you are not using a solar heater.)
Now if you are going to be away for a few weeks, then that would be different.
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Joseph E. Meehan

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Down here in California the heater runs when the pump is on which is only about 6 hours a day. That should be enough both to keep the water clear and heated too. I set the timer to run in the day so noise does not bother neighbors.
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Turning the heat off at night could save energy. A 24'x32'x6' 70 F pool in 60 F air with an R1 cover would lose about 16h(70-60)24x32/R1 = 115.2K Btu over 16 hours. With no heat, and thermal mass C = 24x32x6x64 Btu/F, it would cool to 70-115.2K/C = 69.22 F, with an average 69.61 temp and an energy savings of about 115.2K-16h(69.61-60)24x32/R1 = 2880 Btu/day, about 8 cents per day, at 10 cents/kWh... in the shade.
But the 1981 NRC Solarium Workbook says 5375 Wh/m^2 (1704 Btu/ft^2) of sun hits the ground on an average 12 C (54 F) May day. If 90% of that enters a square foot of T (F) pool with R1 insulation, 0.9x1704 = 24h(T-54)1ft^2/R1 makes T = 118 F, with no extra heat :-)
Nick
Don't miss this opportunity to have every solar question you ever asked answered in four different ways. Space is limited...
Join solar guru Steve Baer and PE Drew Gillett and PhD Rich Komp and me for an all-day workshop on solar house heating and natural cooling strategies ("HVAC Nonsense") on July 9 in Portland, OR--see page 25 of http://www.ases.org/conferences/2004_call_for_papers/SOLAR2004_prelim_program.pdf
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PoolGuy writes:

Run it as little duty cycle as possible to have it up to temperature when you want to USE it; idle it at other times. This assumes you are extremely wealthy. Pool heating is a luxury I suspect you can't afford anyway.
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Thanks everyone for answers.
Thanks to your replies, I did realize that I am running pump just during the day, so to heat pool overnight will require runnig a pump. Altough NicksanSpam calculations shows that savings would be minimal, I still decided to heat pool just as I need basis.
Thanks for all your help

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I have found that it takes my pool heater approximately an hour to raise my pool temperature one degree. Usually during swimming season from late May until late September here in the Carolinas the Sun will only get my pool temperature up to about 76 degrees due to the trees in my yard shading the pool. So, I turn the heater on about 24 hours before I plan on going swimming and this allows my propane gas heater to get the pool up to that toasty 88 degree mark for swimming!
Last summer I made the mistake of just setting the thermostat on the pool heater and leaving it running on autopilot for a few weeks without putting a solar blanket over the pool. Whew...did I burn some propane gas! That was an expensive lesson.
Regards, Bill
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