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What is the best color to paint my swimming pool so it will be warmer? I assumed dark blue, but would silver be better? Answered

My pool is an inground fill & drain with no filter, pump, or pool cover. The edge of the pool is about 2 feet above ground.


Black, but then your pool may look silly.

You could use one of those solar pool covers, but they are sometimes a pain to put on and remove when all you want is a quick swim.

I'd say try to make a solar water heater and use a pump to circulate the pool water through it. If power is a problem, you could look around and find a battery, 12v pump, charge controller and PV solar panel to drive it.

When I was in college a team was working on a project like this for a community pool.
Instead of a solar panels for the heating just get some black rubber or malleable plastic pipe/hose, coil it, and slowly circulate the water through it and back into the pool. It could be cheaper than solar panels. Make sure your intake and output are spaced so you don't heat the same water over and over.
If you start the system early in the season it should be warm(er) by the time you want to actually use it.

Water has a greet-big absorption-band in the IR, I don't think the colour matters that much (with the lid off).


I've been trying to prove that for the last hour. By what depth has 90% of the incident IR been absorbed I wonder.

This helps:
http://telstar.ote.cmu.edu/environ/m3/s2/02sun.shtml (fig 4 for example)
It's both, but I don't know how the lining of the pool distributes heat between the water and the ground. In terms of energy-capture I'd think tonnes of water would absorb more energy than a dark-but-acceptable paint-job?


I agree with you, if the water is as strong an absorber of infra-red. But there is a lot of energy in the visible band too, so the liner colour must help.

Black swimming-pool? That'd be interesting, esp if you could get it really black so you couldn't see the bottom...


But a dark lining will absorb the visible and re-emit as heat, no?

If the absorption is strong, as L. implies, then the energy might be absorbed before it GETS to the lining.

Yes, the IR will, but the visible won't - that is what the dark lining would turn into useful heat.

AFAIK, a dark lining would be best for heating the water, but not so good for using the pool - visibility underwater would be much reduced.

Instead, I would use pool-side solar panels (say, on a fence, or the roof of a shed or garage), with a small (solar?) pump circulating pool water through them to pick up the Sun's heat and transfer it to the pool.

> visibility underwater would be much reduced
.  In the clear water that is normally found in a swimming pool, the reduction in visibility may not be perceivable, even on a cloudy day - you're starting with much more light than you need.

> use pool-side solar panels, with a small (solar?) pump
.  Sounds like an excellent idea.

But isn't that less efficient than a straight pool cover? Solar heating panels, as you suggest, rely on the water absorbing and retaining heat from the sun. So now you take that relatively small volume of warm water and mix it into the pool at ambient temperature. The increase in pool temperature isn't going to be great, I think.

With a simple plastic pool cover, the whole pool acts like a solar heating panel.

Yes, but since you are only heating the top of the water, the convective mixing will be minimal, and you'll end up with a nice toasty inch of water on top....


True - I was trying to suggest something that wouldn't get in the way of using the pool.

Cover the pool surface with dark coloured plastic balls. you can swim through them and they will absorb the solar heat BUT as KM says a dedicated pool side solar heater is going to be more effective.

A pool cover is going to be your best bet. You want to reduce the evaporative losses as much as possible. If you do something to heat up the water, and leave the surface exposed, all you're going to do is increase evaporation, which also lowers the temperature.