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Thread: Solar cover on or off during the day in hot weather?

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    Solar cover on or off during the day in hot weather?

    I was wondering what people think when it comes to having the solar cover on or off during the day in really warm weather? My cover is dark blue. I know it keeps the heat in at night but would the pool warm up more with it off in the daytime? Would it let the sun penetrate right to the bottom and help it heat or is it still better to leave it on when not in use?
    (: Jan :)

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    frustratedpoolmom's Avatar
    Join Date
    May 2007
    SWSuburban Chicago, IL

    Re: Solar cover on or off during the day in hot weather?

    I too just replaced my cheap 6 mil light blue cover with a dark blue one. So I'm not sure yet.... YOu will lose more FC to sunlight with it it's a trade off there. I think the covers heating the water in the daytime - mostly myth - they do more in the way of heat retention at night than actually heating the water in the day. So if heating is your goal and you don't mind losing the FC to sunlight, leave it off during sunlight hours and cover in the evening....
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
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    Join Date
    Aug 2007
    Eastern Canada

    Re: Solar cover on or off during the day in hot weather?

    I'm in Canada where heat retention by solar covers is critical. My rule of thumb is to always use it at night, and to take it off in the day only when the sun is shining and there is little wind (or when I'm using it!). This seems to be the best combination. I do find that when the cover is on and the pump is off on a sunny day that the top 4" of water is very warm, so solar gain during the day is definitely there, but I do agree that the lack of cooling by evaporation (my cover claims up to 95% less evap.) at night is the more important factor, particularly in the shoulder months. With the cover and the pump both off during the day, the same amount of daytime heating may happen, but is more evenly distributed throughout the pool depth. I am not sure how you would determine this.

    Previous discussions here suggest that the clear covers may be better than the dark blue ones for heating the pool during the day. Seems logical to me, but the covers available in this area at a reasonable price are all dark blue, so I haven't been able to test.
    18X36' 25000 gal Jacuzzi vinyl Inground Pool (1985) with resin sidewalls, newer Jacuzzi 1 hp two-speed pump and sand filter. Raypak propane heater, Rainbow 320 chlorinator (mostly use bleach).
    Softtub 220 portable hot tub.

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    Re: Solar cover on or off during the day in hot weather?

    Thanks for the info guys, I'm going to try it without during the day for now when its hot out (32 degrees today!) and see how it goes.
    (: Jan :)

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    MikeInTN's Avatar
    Join Date
    May 2007
    Middle Tennessee

    Re: Solar cover on or off during the day in hot weather?

    I'll throw my .02 in here. When it gets hot here in Tennessee (July, August, September) with 90 degree days and high - 70 degree nights, I leave the cover off night and day. I find that the pool stays around 84-88 degrees, and if we get a stretch of extremely hot weather (high 90's in the day, low 80's at night) I'll usually have to run a fountain to cool it down some.

    As Derek pointed out, the cover also helps reduce cooling by evaporation during the daytime as well, so during the "iffy" months I'll keep it on during the day when not in use. Also helps cut down on the chlorine loss!
    24' x 52" AGP - approx 13,500 gallons
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    Intex 8110 SWCG
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    NWMNMom's Avatar
    Join Date
    Apr 2007
    Waaay NW MN

    Re: Solar cover on or off during the day in hot weather?

    When we get very hot weather I run my pump and water through the solar panels at night - really does cool that water right down.

    I find that my water heats MUCH faster with the cover off on hot sunny days unless there is a lot of wind. The cover on at night is a MUST though for most of the time to keep that heat in. We rarely have issues with it being too hot here. We had frost yesterday morning.
    18x33x52 Buttressfree Seaspray (Wilbar) AGP - 1.5hp Pentair Maxim w/22" Pentair Meteor Sand Filter, Aqua Rite SWG System, Biltmore Walk In Steps - 2/4x20 Solar Panel Setup - Doheny Jet Drive (RIP -Pool Rover Jr) - finally hard plumbed the whole darned thing -
    Beats Driving to the Lake!

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    Cherie's Avatar
    Join Date
    Jul 2008
    Wylie, Texas

    Re: Solar cover on or off during the day in hot weather?

    We laid out our solar cover today to cut it and didn't get around to cutting it for a few hours. By the time we got around to it, we were surprised to find the ground under the cover was really warm! We had it bubble-side-up on the ground. So we hit 95 today outside, but our water is still only 76 Hopefully, the solar cover will warm the water up to at least the low-80's by late tomorrow afternoon and we can take a dip when we get back in town
    32x16 buried Doughboy, 4' shallow - 7' deep
    Pentair Dynamo 1 hp, 2-speed - Pentair 150# SD40 w/zeolite (75#)
    One skimmer/two returns/Aquabot Turbo T2

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