DIY Solar Pool Heater




Introduction: DIY Solar Pool Heater

Last year my Wife and I bought an above ground pool for exercise and recreation. We discovered that my Home shadows the pool in the afternoon, and that drives the water temperature down several degrees in the Spring and Fall. Since we usually don't get into the pool on Weekdays until after work, this made for some pretty chilly swims, even when the air temperature was in the 80's. I decided that a Solar heater that I could mount outside the shadow of the house would be just the thing to bring the water temperature up to more bearable levels.

Step 1: The Solar Collector:

I took a 4x4 piece of plywood and painted it black. Then I took 200' of 1/2" vinyl irrigation hose and coiled it tightly on the plywood, using UV-resistant zip-ties to secure the hose every foot or so by drilling holes and looping the zip-tie around the hose and through the plywood. As you can see 200' doesn't completely cover the plywood, but since I was following the square edges instead of using a circular coil I ran into a problem where the hose started to kink in the corners. If you look closely at the picture you can see I still have a few kinks to literally work out.

All done, and in the Sun, I took a temperature reading of the surface of the board at about 3:00 PM. The surface read about 134 degrees F.

Now we've got to get that lovely heat into the pool.

Step 2: Valve Assembly:

I put together a series of valves and "Y" adapters to route the water into the heater and then back to the pool, using the natural flow and pressure of the existing pool filter pump, instead of a separate pump. The 1/2" ball valves allow me to shut off the water to and from the solar heater and remove it once the afternoon temperatures make it unnecessary.

Step 3: Water to the Solar Heater:

The top is a smooth 1 1/2" "Y" adapter with a 1 1/2 to 1/2" threaded adapter in one side with a 1/2" male to male threaded nipple to a 1/2" ball valve and a 1/2" threaded to ribbed adapter that the vinyl hose slides on. I used two hose clamps on each hose fitting to avoid leaks. Sand all smooth surfaces prior to gluing to assure a good seal. IMPORTANT: Do NOT glue any threaded parts. The glue will set long before you get the threads tight. Use Plumbers Grease or Pipe Dope to seal the threads. Even Teflon tape may leak due to the high pressure.

Step 4: Regulator Valve:

The middle valve is a smooth 1 1/2" ball valve glued to a short piece of 1 1/2" PVC on both sides. By partially closing this valve the pressure will divert some water out of the top "Y" adapter to the solar heater panel.

Step 5: The Return Valve:

The bottom of the assembly is pretty much a mirror image of the top. A ribbed to 1/2' threaded adapter to a 1/2' threaded ball valve, to a threaded 1/2" to 1/2" nipple, to a 1 1/2" smooth adapter, to a smooth 1 1/2" "Y".

The flow of the water down the 1 1/2" PVC pipe through the 1 1/2" ball valve will draw the water from the solar heater into the water that flows into the pool.

Step 6: Timer:

If the water were allowed to constantly flow through the solar heater, the hundreds of gallons of cold water in the pool would overwhelm the 10 or so gallons of water in the solar heater. It simply wouldn't have enough time to heat up before it got sent to the pool. To solve this I installed an outdoor timer to my pool pump. The pump still runs several hours a day to filter the pool, but from Noon until about 6:00 PM the timer turns the pump on and off at 1/2 hour intervals. This gives the water in the solar heater time to heat up before it goes into the pool.

Step 7: Hot Water:

As you can see, the water flowing into the pool when the heater is operating is about 99 degrees F. This keeps the entire pool at about 84-86 degrees in the shade. Everything was purchased at Home Depot and cost about $50.

Now my Wife and I can get into the pool with an "Ahhhhh" instead of an "OOOOOOoooo".

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65 Discussions

I was wondering.. i have trouble finding the plumbing like this... where did you got it?? thanks!! nice project BTW

I might have to look into something like that. Since my system is connected to the pool's plumbing, it causes the system to use too much chlorine.

Genius ! Great Job !

Garden Hose as collector : I made a Portable Solar Pool Heater 1,04 k Watt DIY, first I used a garden hose, now a Intex Solar mat. So the module is Foldable and Portable. No need of electricity ! No sun, or clouds: the pumps stops.

I have discovered a drawback to my design. Because I am turning the pool pump on and off more frequently that I would without the heater, my automated chlorine infuser is putting too much chlorine in the pool. Now that is Summer, and I don't need the heater, I need to reset the timer.

Your collector seems to warm (130°F), you lose a part of collected energy before it goes back to your pool. A solution could be to augment water flowrate. It is a common mistake to want hot water at the output. Look at this chart:

A good question. Since it is actually irrigation hose, and not meant for above ground use, I really couldn't say. There might be some UV issues since the heater is meant to be pointed at the Sun. I had it disconnected (and in the shade) during the hottest part of the Summer, but I reconnected it last week.

Maybe try painting over the hose for UV protection? Just a large can of black spray paint might help with the UV breaking down plastic.

I wonder if by turning off the pump you are allowing the water to separate into a warm layer on top and colder water underneath. So it geels warmer to get in and the thermometer reads a higher temperature but overall the water is not warmer.

The guideline for solar pool heaters is you need panels at least half the area of the pool surface to be effective. So I think you need to make about 10 more collectors to make a real difference to the pool temperature.

1 reply

I think that would be likely if the pool was stagnant. But since the pump runs several hours a day before and after the half hour cycles, it mixes pretty well.

I guess I should weigh down a thermometer to the bottom of the pool and compare readings.

I want to say thank you to you and other great insctructable who make me very happy. See my photo. Thank you so much, Elio from Italy.

1 reply

Very good! You got the best of both worlds. The solar heater and the dark pool cover.

If you placed some black plastic sheets floating on top of the water it would heat more efficiently and faster. I did this once and had great results. Even if you don't get 100% sun coverage, it might be enough to keep your pool warm. It warmed our pool to where we had to make a few smaller floating sheets. We'd control the temperature by removing the sheets.

4 replies

It doesn't even have to be black plastic. Most of the light that passes through the water surface will be absorbed by the water and converted to heat. Most of the heat in the pool is lost through water evaporation. anything that slows the evaporation loss will help heat the pool.

Many people attach black plastic to hula hoops. Clear plastic will also work especially if you place the hoop in the water with the clear plastic on facing up. That would create a insulating layer of air between the plastic and water surface. Another option is to use clear pastic bubble packing sheets. Simply cut it to size and lay it on the surface of the pool when the pool is not being used.

I was going to go with the black plastic (I was going to use garbage bags and hula hoops). I just thought the solar panel and valve assembly was cool. :)

We made a bunch of 'lilies' and decorated them. We'd take them out whenever we went swimming. Depending on how warm we wanted it we'd throw in an extra lily or two. It worked great and had no moving parts.

For all the timer questions: Yes, I did run the system initially without the timer and the water running all the time. The pool temperature at 6:00 PM would usually be about 76 degrees with the air temp at 84. When I installed the timer and ran it at half hour intervals from Noon until 6:30 PM, the pool temp would be 84-86 degrees.

All I can tell you is that it works.

1 reply

Keep in mind that the collect is acting as both a radiator and a heater. if you are circulating the water very fast through the loop it may loose more heat than it gains when the air temp is cooler. If you run it very slowly the water will get hotter than the air and radiate heat away into the air before it gets back to the pool.

By adding the timer you basically did nothing more than throttle the pump down. An alternative to a timer is a valve. Adjust the valve to slow the flow of water through the tubing. If you use a low flow pump or a valve you might want to add a device to measure the temperature of the collector. If the collector is cool turn off the pump. When it gets hot turn the pump on. That way you avoid loosing heat due to clouds or a cold morning. You might want to search the indestructible website. there are other post of such projects. several I have seen have use a circular coil. Water enters the center and spirals to outside where it leaves the collector. This method avoids the kinking problem you had.