Pool Solar Water Heater




How to build a solar pool water heater.

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Step 1: What You Will Need

When you live in Canada, you need to turn up the heat in your pool all summer long if you want to use it.

First off, you need a location to install the heater. Preferably, if you live in the northern hemisphere, a southern exposition. The location should have as much sunlight as possible all day.

That said in terms of supply and tools , you will need:

L shape metal rods (or wood it you prefer)
2 x 64 inch 1 1/4 inch diameter copper pipes
3-4 rolls of 1/4 inch copper pipes.
Tin solder
Soldering paste
Welding torch (bernzomatic, plumbers stuff)
Pipe cutter
Chalk line
Automatic punch
Measuring tape
Broom stick
Acetone or other cleaner that can remove soldering paste
Plumbers tape

Step 2: Making a Frame to Hold the Pipes

I think you could probably builds the frame out of wood or other material. I decided to build this with L shape steel rod.
Cut the rods to length to make a rectangle. on the shorter side , I made some notch with a hole saw, so the pipe will fit in. Weld the rectangle together. If you don't have a welder, or access to one. You could also drill and bolt the part together. I used some rubber to isolate the steel frame from the coper to prevent metal reactions.

Step 3: Drill the Manifolds

Drill 1/4 inch holes in a straight line into the 1 1/4 inch pipe to make two manifolds. I made holes every other inch for a total of 63. In order to make a straight line, I used a chalk line.
insert the pipes onto the frame so you can evaluate where to start and stop drilling holes.
This way you will not have any holes where the manifold pipe will attache to the frame.

I have evaluated the 63 1/4 pipes will have more then 3 times the diameter of the 1 1/4 " pipe. this is to make sure the water will slow down a bit in the smaller pipes.
By slowing down the water a bit , It helps with the heat exchange...

Step 4: Drilling

I made a jig to align the pipe onto the press drill. Pre marked and punched the pipe every inch.
Just drilled away 126 holes. (63 per pipe).

Drills don't make perfectly round holes, so use a hand borer tool to make it rounder, and made it to fit as snug as possible for the 1/4 pipes.
try and fit every 126 holes with a sample pipe.

To make a perfectly straight line on the pipes, attache them together with clamps , then use a chalk line where the pipes touch each other.

Step 5: Cutting and Fitting the 1/4" Pipes

Unroll and cut the 1/4 inc pipe. Make a jig, and try to make the pipe straight while unbending it slowly onto the jig. I suggest you mount and secure the 1/14" pipes to the frame. Make sure the distance is the same between both pipes.

Cut to the 1/4" pipes so that they are about 3/4" longer then the distance between the to 1 1/4 pipes. This will ensure, once you insert the small 1/4 pipes into the holes of the manifold pipes, that there is a bit more than 1/4" exceeding inside.

Step 6: Prepare for Soldering

Like any plumbing job involving copper pipes, you must prepare the copper very well.
Take a medium sandpaper, and sand any oxidation everywhere you will have to solder the pipes together.

Sand inside the 1 /14" pipes. attache some sanding paper using double sided tape on a broom stick and sand the inside in line with the holes. this will get rid of the drill shrapnel and will help the thin to make a better bond.

Sand all of the 63 1/4 pipes end. (about one inch on each end)

Step 7: Assembling the Small Pipes Into the Manifolds

Insert every 1/4" pipes into the holes on each side. insert the small pipes into one side, then back into the other side. you can insert a piece of wood to align the pipes inside.

Step 8: Soldering the Pipes

Apply soldering past to the area you will be soldered. You can even put some on every end of the 63 pipes before you assemble them to the manifold pipes.

Soldering is a precision and a patience thing. take your time. It took me about 1 and a half hour, and I'm not a pro. (I'm an electronic automation eng.)

At each apposite end, solder some 1 1/4" fittings to enable you to screw an adapter in order to convert from 1/14 to 3/4" flexible pipe

the other ends will have a welded cap.

Notice that water must come in on one side of the first manifold, and come out on the other side of the second manifold. This will ensure that water will travel the complete distance. (like in commercial heat exchanger)

Step 9: Pressure Test

Before going any further, it would be a good idea to do a pressure leak test.

Connect a water hose to one of the 1 1/4 pipe and a small piece of hose on the other side.
You can mount the 1 1/4 adapter to bring it down to the 3/4.

Turn on the water to flush out the air.

When the air is out, bend the exit hose to stop water from coming out.

Check every soldered joints for leeks. If there are any, completely empty the heater, and retouch.

For those of you unfamiliar with soldering pipes, If there is water inside the pipes, you will not be able to solder them properly.

Redo the test until it's perfect.

Step 10: Cleaning

Clean off all of the solder paste left behind.
Using Acetone, will remove all of it, and really make the metal ready for painting. (make sure it is perfectly dry, acetone and paint is not a good mix for a nice finish)

Step 11: Paint

Use a black mat paint, in spray can or regular. I used both, the spray for the copper, because it's easier to spray paint the small pipes. I used a regular paintbrush for the steel frame to have a thicker quote.

Step 12: Final Assembly

Assemble the 1 1/4" adapter to downsize the pipes to 3/4.

Step 13: Installation

Find a good place were there is maximum sunlight all day. My installation is facing South ( I am in Canada). Anywhere in the southern hemisphere is facing north I assume)

Bolt the water heater on a rooftop or anywhere that is in the sunlight and convenient for you.

Use 3/4 inch plastic tube from the pool filter pump output, to the bottom manifold.
From the top manifold, use a 3/4 inch pipe and go back to the pool.

You can use flexible general purpose, low cost pipes.

You can use 90deg angles to come down from the roof. custom fit the hoses and secure them to the side of the house or whatever it's sitting on.

Step 14: On the Filter and Return

Get a 3 way pool valve. insert this valve between the filter and the pool return pipe.
Add a converter from the pool size pipe, to 3/4" fitting.
Insert the pipe going to the water heater on the 3 way valve.
With this valve, you will be able to regulate the flow of water going into the heater.

Step 15: The Final Result

You probably noticed that I added a glass over the water heater. This is the corrugated type you install over a patio. It's much cheaper then Plexiglas . I pick up a 8'x36" for 19.00$ at home depot.
Plexiglas or acrylic was in the 200.00$

This make no difference in the heat result. It was more because since I live in Canada, I need to protect the fragile 1/4 pipes from bending under the weight of the snow in the winter.

Over all efficiency so far : (tested for 3 weeks from May 17 to June 6 using a calibrated lab mercury thermometer)

Delta T ( temperature difference):
With an outside air temperature of 21C (70F) and the pool water at 17C (63F) the heater turns water from 17C (63F) to 22C (71F) in one day.

Water coming out of the heater is about 3C (1.8F) warmer then the input .

Keep in mind that this data was recorded in the last weeks of May. We are in the spring in Canada (Laval, Quebec) latitude 60 00 longitude 95 00 W

The sun hits the water heater on the roof from 10:00AM to 3:30 PM that's 5.5 hours
Anyone in a warmer and sunnier environment should get much better results.

I just added some black pieces of metal under the 1/4" pipes and blocked off the sides to get more heat. so far it's hard to say it if it make a really big difference.
If I was to make an other one, I would make it twice the size.

Step 16: Swiming 2nd Week of May

For anyone south, swimming in May is probably normal, for Canada, it's exceptional...
Average temperature outside has not gone over 21C ( 68F) and was more in the 17-18C (62-64F)


Pool specification
15' round 52" high
Filter with a 2 speed pump

Location of the heater
It's on a small roof over the balcony, about 18' higher then the pump.
I must use the second speed to start the water from flowing to the heater. Once it primed , I bring it back to the low speed and gravity does it's job.

Have fun , and please make this design even better if you can!

Richard Marier

1 Person Made This Project!


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95 Discussions


Question 1 year ago on Introduction

I really like the design and effort that went into this. I do believe that if you kept the pipes flat black and put reflective material like foil and foil tape on the interior walls and bottom of your box it would be more efficient. I wouldn't use a smooth textured medium such as a mirror because you want the radiant waves to scatter behind and around all sides of the pipes. A totally black box will absorb heat but also reject it in all directions like to the roof shingles. Focus the radiant waves to just the pipes otherwise you have a hot box relying on air around the pipes to heat the pipes.


10 years ago on Step 16

To prevent the copper discolouring the pool you really need to place a heat exchanger at the pool end, I am sure this could be made out of PVC tube, it will allow you to keep the solar heated water seperate from the pool water, that way you can fill the solar panel with antifreeze to prevent damage in the winter. To increase the performance you should install a metal collector place to the back of the pipes (painted flat black) and enclose the entire collector in a wooden box to prevent the wind from cooling the collector (some insulation at the back would also help). With these modifications your panel should yeild 4 times more energy and make a positive impact on the pool temperature. Insulating the pool and installing a thermal pool cover (bubble wrap) will allow you to retain the heat and reduce evaporation. This is a great project, well done!

2 replies

Reply 2 years ago

No heat exchanger is need whatsoever, one only needs a proper balanced pool to prevent copper scaling or copper staining (both are the result of improperly balanced pool water). Properly balanced water WILL NOT attack Copper (hint: homes used copper water plumbing for a century). Copper Scaling is caused by pool water that doesn't have a proper level of Calcium Hardness (150 - 200 ppm for Vinyl, Fiberglass, or Painted; 300 ppm for plaster/concrete) and a pH of 7.6 or higher (water becomes caustic). When the pH gets to high, water "Attacks" the copper and it precipitates out of solution causing scale and blue green water. Copper Staining is caused by improper CH level with a pH below 7.0, the pool is now acidic and again "Attacking" the cooper causing Staining. The lower ones CH is the faster this happens as CH helps tame aggressive water molecules.

I use Copper Ions as my sanitizer and use no chlorine whatsoever in either of my pools and even with using Copper as my sanitizer intentionally putting 0.5 ppm in my pool, my water is crystal clear and is cleaner/safer to drink then the water coming out of my tap from the County Water Company! I only need to check Calcium Hardness twice a year, phosphates once a month (or after heavy rain), check Copper Ion level once a week, check Alkalinity once a week, check pH twice a week (keeping it between 7.1 and 7.3), and every Sunday evening pour one gallon of hydrogen peroxide around the edge of my pool (plus adding one gallon after heavy bather load or party).

The heater has been working for the past 2 months and there is no visible water discoloration. the PH is always perfect and the chlorination is as usual. we test every 2- 3 days and add some if needed. We try to keep it at the minimum in the acceptable range. We add at night and test in the afternoon.


5 years ago on Introduction


I suggest you add a box around it to close it, with a glass overhead... as well as a reflective plate on the bottom.

I was able to harvest more energy from it.

I also added an anode in the pool to prevent the copper from corrosion

A friend of mine made the same thing from PVC... it is about 75% as effective
He made it with small PVC tubes just like my design...Keeping the small tubes gives off more surface contact...

If this is on a roof, I suggest using CPVC as it has a higher resistemce to heat

If you leave it out in the sun while it is not working... PVC start to fail faster

Good luck and have fun!


7 years ago on Step 12

Why does it enter through the bottom? To slow the water flow?


10 years ago on Step 16

Overall this was a nicely done instructable. I do however have a few comments. 1. The steel frame is welded, but copper is either brazed or soldered (you were soldering). 2. PVC or CPVC would be much cheaper, last longer, and is easier to work with. 3. You really need to have either a reflective surface under the tubing or a flat black. Reflective surface will allow the tubing to receive the light a second time, flat black will absorb the light and provide some radiant heat. 4. You would be better off using a small pump that is separate from your circulator, unless you run your circulator continuously.

9 replies

Reply 7 years ago on Step 16

regarding: https://www.instructables.com/id/Pool-Solar-water-heater/step16/Swiming-2nd-week-of-May/

Wouldn't the system have ben more efficient has the plumbing been ran in series rather than parallel? Thank you.



Reply 10 years ago on Introduction

PVC is cheaper, BUT you will not get the heat transfer that you get with copper. Still the best bet for transfer of heat energy. Great Idea.


Reply 10 years ago on Introduction

Thanks for pointing out the proper word usage, English is not my first language... (I'm in Canada and mostly use french ) we use the word "souder" the equivalent of soldering I guess. There's not really any welding equivalent, as we use the same word "Souder" for both. I do understand the difference. I will change the words in the instructable. Thanks


Reply 10 years ago on Introduction

Interestingly enough "souder" is used to explain how the word "solder" is to be pronounced, in English.


Reply 10 years ago on Introduction

Only Americanglish- in the UK we pronounce the L in solder, so it sounds like smoulder without the M.


Reply 10 years ago on Introduction

Ah, English. I'm an amateur radio operator. While listening to an Aussie and a Kiwi give a Texan a bad time about his drawl, the Aussie remarked to the Kiwi, it's those Limeys who really talk funny. ;)


Reply 10 years ago on Introduction

You telling me that we Aussies talk funny? I think you're wrong. It's the Kiwi's that talk funny, Not us!


Reply 10 years ago on Introduction

Didn't say that you Aussies talk funny, just that one Aussie, and one Kiwi where in agreement that the Limeys talk funny.


7 years ago on Step 3

This project looks really complicated and time consuming.
Wouldn't it be better to simply lay black plastic pipes
in sleeves inside the box?


10 years ago on Introduction

Salut Richard, Tu a raison pour la température au Canada (Québec) moi ja l'ai fait il y a 4 ans, avec des tuyaus d' ABS et de la colle ABS 4 pieds par 20 pied et ca marche!!!! moi j'ai une 18 pieds et mon eau est entre 80º & 86º Merci Christian

heat pool.jpg
2 replies

Reply 9 years ago on Introduction

 You will get a more uniform flow through the vertical pipes if the manifold pipes (top and bottom) have the inlet and outlet at opposite ends (one left, other right).

Other wise the greatest vertical flow is closest to the connections.