Introduction: DIY Solar Pool Heater

Picture of 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:

Picture of 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:

Picture of 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:

Picture of 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:

Picture of 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:

Picture of 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:

Picture of 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:

Picture of 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".


bnaivar (author)2017-06-21

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.

andrefierens (author)2017-06-20

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.

bnaivar (author)2016-07-17

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.

andrefierens made it! (author)2016-07-16

Great Job ! I like it !

I made a Portable Solar Pool Heater 1,04 k Watt DIY

ArnaudM21 (author)2016-07-11

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:

MichaelKMoser (author)2015-09-01

Great long will the hose last?

bnaivar (author)MichaelKMoser2015-09-02

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.

indysilverwing (author)bnaivar2015-11-05

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.

AMRANE77 (author)2015-07-22

very good idea

electric_piano_5k (author)2015-07-05

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.

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.

Elio23 (author)2015-06-30

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.

bnaivar (author)Elio232015-06-30

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

bd5 (author)2015-06-23

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.

steven4872 (author)bd52015-06-29

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.

loki2012 (author)bd52015-06-24

I like this idea. Very simple!

bnaivar (author)bd52015-06-23

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. :)

bd5 (author)bnaivar2015-06-23

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.

bnaivar (author)2015-06-23

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.

steven4872 (author)bnaivar2015-06-28

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.

Blocos27 (author)2015-06-27

I realized this pool heating on a pool that is 10 m3. With sunshine from 9 AM to 3 PM I increase the temperature of 4 ° to 5 ° C.
It is important to find the right speed that allows the best calorie shifting. To this I added a second pump 2 m3 / h for heating and I drive all with an Arduino to not exceed the maximum temperature of 30 ° C (beware of seaweed ! )

loki2012 (author)2015-06-23

I have been thinking of building something similar, using a "solar" powered fountain pump to run it while the sun is out. The pump may not move a lot of water but I figure that it will still heat and cycle the water (as long as there is not a lot of height to over come). Any thoughts on this would be appreciated before I spend money!

tjfoley (author)loki20122015-06-23

Make sure the pump is rated for hot water searh on Ebay for solar pumps they are preety cheply priced!

Blocos27 (author)tjfoley2015-06-27

Solar collector must be AFTER the pump.

bnaivar (author)loki20122015-06-23

There are a couple of YouTube videos where people placed their coils of tubing on the roof of their house or shed. This would create a natural "head" to assist the flow of water. Once the water is moving a small pump should be able to keep it going. I couldn't put my tubing on the roof because I needed the heat in the afternoon and my roof faces away from the Sun in the afternoon.

millmore (author)2015-06-24

I'd be interested to know what happened if you didn't turn the water on and off. I think it's actually making things worse for you. Heat loss is proportional to temperature, so if you heat the water in the collector to 99F, more is going to radiate away than if you heated it to 90F for example. It should be much more efficient to keep the water flowing through the solar collector all the time, and raise it by a tiny amount as it passes through than it is to have it stop,heat,go,stop,heat,go. Heating 1000 gallons by 1F has the same effect as heating 100 gallons by 10F and mixing it in, but you get less heat loss in the system with the 1F rise. That's how air source heat pumps work on pools - little and often.

Although, if you are achieving the desired effect anyway, who cares?

CecilC1 (author)millmore2015-06-26

that is why sizing the system is important. improvements on this design would be to use a small 12 dc variable speed pump ran off a pv panel size the system just big enough to heat the pool up on the coldest summer day. build a controller to slow down and speed up the pump as needed. add some check valves.

Mugsy Knuckles (author)2015-06-25

It occurs to me that if this array were placed lower than the pool water, no pump would be needed. As the water in the coil heats it rises, moving the warmer water into the cooler pool, and the cooler pool water would go down into the coil and the process would be continuous (as long as it's sunny). I'm sure this would work if the coil were in say, a fire, so I assume it would do the same in sunlight, albeit much more slowly.
I suspect that without another heat source you'd need about 4.2 million square miles of this to heat a pool up any appreciable amount.

CecilC1 (author)Mugsy Knuckles2015-06-26

it would take the apox. same sq feet of tube as the pool surface. also this is only good for small temperature delta's( the larger the tempature difference the less effective it becomes.

juanvi (author)2015-06-26

Nice. I'm working on the same project.

The timer is useless. The solar collector will heat the pool the same. You transfer the same energy by having a constant flow through the solar collector or by having it replaced and heated up. Actually, the more temperature difference there is between the water going in and the solar collector, the faster the thermal energy will transfer, so you should even get more out of it if it is constantly running water through the collector.

rrichardson-1 (author)2015-06-23 friend had one...if you build a box/frame of 2x4"s around the edge and cover with clear plexi-glass you will increase your temp/efficiency quit a lot.....keeps the heat in,

bnaivar (author)rrichardson-12015-06-26

rrichardson-1: That's probably my next step. Now that I've countered the afternoon shade cooling, I can do that to try and extend my pool season into Fall.


bnaivar (author)2015-06-26

;) (author)2015-06-24

Its always good getting heat for free, and great job hooking it into the pump. I have to agree with rrichardson-1, you are losing a ton of heat by not having it inclosed.

BG_instructs (author)2015-06-22


i build exactly the same thing some 3 years ago and already scrapped it.

The PVC tubes simply do not exchange heat that good, you should use copper pipes, works so much better.

Where i live, in full sun, the water barely reaches 24 to 25 Celcius, the solar exchanger helped 2 degrees on very sunny days.

I even covered the whole thing with a translucent plate to avoid wind cooling the tubes down again.

It was fun to build and experiment, but it turned out not that great, copper tubes would cost too much, i would install a heatpump; insert 0.65 KW, extract 3KW of heat, gain 10 degrees in 36 hrs, sun or no sun.

"... i would install a heatpump; insert 0.65 KW, extract 3KW of heat, gain 10 degrees in 36 hrs, sun or no sun."

BG, would you elaborate on your heatpump idea some? Sounds quite interesting.

Have to use a translator, but this is a off the shelf product. 3 solarpannels on your roof can generate enough enegy to drive the 650 Watt required, the heat exchanger itself extracts 3Kw of heat out of the air.

sundug (author)BG_instructs2015-06-23

Chlorine and bromine react with copper, discoloring the water.

bnaivar (author)BG_instructs2015-06-22

I can see where you'd have poor luck with this. If you start with water temps like that, the pipes can't put enough heat into the pool to bring the entire thing up more than a couple of degrees. I had the advantage of the water warming up during the day and then the solar collector only had to keep the water temp from going down drastically when my house shaded it in the afternoon.

calyad (author)2015-06-23

This is a great idea, Bnaivar. My husband brought home a second-hand spa. The water is VERY cool. It has a heater in it, but we want to conserve power and a solar heater like this would be just the thing. Maybe your instructable will give him some ideas.

tjfoley (author)2015-06-23

I like your idea you got the almost all the stuff to make a solar pond. Same basic idea except you put you coil in a heavy brine (Salt will work too) solution fill you pond about 3/4 with the salt water then add fresh water cover with clear plastic or glass. I think there is an instructables on making a solar pond.

jredding (author)2015-06-23

Nice build, BTW. I like using the pool pump much better than some add on pump. Good work!

bnaivar (author)jredding2015-06-23

I'm too cheap to buy another pump. :)

SteveAZ (author)2015-06-23

Hi, Good project! I think I'll try something like this for my pool. BTW you don't need a timer just let it flow!

jredding (author)2015-06-23

Only question I have is this: Does the timer actually help?

Sure, it makes the water going in hotter, but it means less water going in. Since the thermal exchange rate is fixed, running the pump continually, rather than periodically should add the same amount of energy (joules).

In other words, if you ran 5 minutes on and 5 minutes off, and got an 8 degree output lift, then running for 10 minutes straight should result in a 4 degree lift - but for twice as much water which means the total energy is equal. In fact, running continually might actually provide more net joules into the pool since more heat would go into the water and less heat would be dissipated through the plywood and the irrigation hose during the times the pump wasn't running.

Does that make sense?

ramses (author)jredding2015-06-23

I agree with you wholeheartedly.

The only advantage would be reducing the electrical power consumption of the pump.

stvangel (author)2015-06-23

I would recommend switching to a solar pump for the heating loops. You have plenty of room in the middle for a small solar cell. The point is that the solar pump would only run when the sun is shining enough to drive it. If you pump water through it when it's dark or cloudy you're actually cooling your pool ( black emits heat just as well as it collects it ).

It doesn't matter how hot the water gets in the pipes, it's a matter of how much heating you have available. If you push 100 gallons through that only gains one degree versus 10 gallons through that gains 10 degrees, you've gained the exact same amount of heat. You're heating is directly controlled by the surface area of your piping system.

By going to a solar pump, the whole thing becomes pretty much automatic. The sunnier it gets, the more it pumps. When it's cloudy it slows or stops.

ItzRulez (author)2015-06-19

Hey, i really liked your idea!

But i have a question, would a constant flux be better for heating the pool?

Considering the Heat Conduction Equation, a bigger difference in temperature, would lead to a bigger heat flux, don't?

And remembering that your only font of heat is the sun, and directly its the solar panel.

I'm really interested in your answer! If you got practical knowledge would be better!

(sorry if i mistaken any english, not my main language)


jfuredy (author)ItzRulez2015-06-23

Yes, a constant flow of water would yield greater heating overall, for exactly the reason that you state. The longer the water sits stagnant in the black tubing, the hotter it gets. The hotter it gets, the less heat it can absorb because it's closer to the temperature of the heat source. A continuous flow of water will maximize your temperature difference, which will maximize your heat absorption.

DGW (author)2015-06-23

I made one of these using 400 feet of discount 5/8" garden hose painted black on a black 4x8 plywood sheet. Put it on the roof facing south. Instead of timing the pump on and off I set the Y valve so that a trickle went to the heater and most of the pump output went to the pool. The heater output went directly from the roof, under the deck directly into the pool for the shortest run of hose. The trickle into the pool was about 100 degrees until late August when it declined quite a bit. Letting it run "cool" for "greatest efficency" may be efficent but will not heat the water above some minimum value. You need to put hot water in to get the temperture to rise. Make sense?

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