Solar Cover


LifeTime Supporter
Jul 23, 2010

My understanding of a solar cover is that it heats the pool by slowing evaporation of the water.

Obviously, night is a perfect time for this.

But I have also read that solar covers actually block some of the sun, and prevent heating.

So on a typically, 80 degree, sunny day, is more heat gained by removing the cover, or by leaving it on?

Always wondered this.


Mod Squad
TFP Expert
Apr 4, 2007
SW Indiana
My guess, strictly from a heat gain perspective, is that on a nearly windless day with air temps higher than water temps, you are better off with the cover off. Otherwise, I think you'll be better with it on up until you have really warm air temps.


Well-known member
Jan 27, 2010
Central Valley, CA
Just put mine on this week and I'm leaving it on except when in use. I've seen a big difference bringing my water temp up from 68 to 80. We were hitting upper 80's midday but probably only for a few hours with lows in 50's. We are full CA sun so I think the blue absorbs the heat of the sun throughout the day.

I don't have the option of being home to remove in the afternoon when air temps are higher.


LifeTime Supporter
Jul 23, 2010

I think it has less to so with actual ambient air temp and wind(which should be close to a non factor), that it has to do with sunlight. The temp of the areas in the sun can be easily 20 degrees warmer than actual air temp. And since all solar covers actually impede a percentage of that sunlight from penetrating--there in lies the question. Is the benefit from evaporation of heat greater than full sunlight penetration during the day. I understand there are many, many variables in this, but didn't know if there was some standard general rule on this.

AS always--I overthink the situation.....


LifeTime Supporter
Jan 11, 2009
Cupertino, CA
Evaporation is a major source of heat loss, and the main thing that a solar cover does is cut down on evaporation. (My understanding is that wind affects evaporation rate so that actually would be a nontrivial cooling factor for an uncovered pool.) The volume of water lost through evaporation is significant; I recently took my old decaying cover off about 2 weeks before the new cover arrived. Replacing 2" per week was a bit of a shock, compared to more like every 5 weeks with the cover on.

The actual heating (as opposed to loss prevention) is less with the cover on than with the cover off, because having the sun heat the cover which then conducts heat to the water is inherently much much less efficient than the sun directly heating the water. But, I think preventing the heat loss is a bigger factor than the loss of direct heating.

That said, in my experience, the solar cover heats up in the sun, which conducts to the water in the pool. This clearly heats up the top two inches or so of the pool (the effect was quite obvious to both my thermometer and the hand I was holding it with). If the pump is off, that's about the only effect; there's no significant conduction/convection warming the main body of the pool water (the warm water prefers to stay at the top). With the pump on, the water warmed by the cover is replaced by cooler water and the heating efficiency goes up. Whether this is a huge difference, I can't really tell; it seemed to make a difference in my pool.


LifeTime Supporter
Jul 23, 2010
Ahh--I was looking at wind speed as it effects temp, completing ignoring the evaporation effect of higher winds speeds--great point.

I have come to the conclusion, at least this time of year in the Midwest, that cover=warmer water.

Thanks for the replies.
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