Last summer when covid meant no visiting beaches or other people’s pools, we decided to get a pool for our own yard. We got one of the Intex “East Set” pools which you plop in place and add water. Okay, actually there’s more involved including clearing the space where the pool will be of any rocks, installing a safety fence, and all of the associated maintenance. But it’s easier than most aboveground pools and much much cheaper than an inground pool. But even our small pool doesn’t warm up as much as we’d like. Sure, you want the pool to be refreshing, but not painful, bracing, or even exhilarating. And a cold pool is one that isn’t used much. Which makes even the low amount of money spent on the pool and fence and water look like a bad investment. So it doesn’t take long after the initial swim before you start thinking “there’s got to be a way to warm up the water”. In the end, I came up with a fix that worked really well for me, wasn’t too expensive, and actually did warm up the pool, at least enough to make it worthwhile. The full story follows the picture of the finished project.
Disclaimer: I’m just writing up what I did. If you choose to use any info here in doing something for yourself, you accept all liability for whatever you do.
There are some pretty amazing devices that will heat the water. But given that this pool is intended to be a cheap temporary thing, I didn’t want to spend a lot of money on accessorizing it. Also, I don’t want to spend utility money on heating it on an ongoing basis. Besides, if the weather is hot enough to be in the pool, surely the sun would be useful to heat the pool. The idea is that you can run some of the pool water through a coil that is exposed to the sun such that when it returns to the pool, it is warmer than when it left. And when you consider that the typical Intex East Set pool is small, that seemed likely to make it worth the trouble.
I found a number of YouTube videos that sort of covered the idea I was aiming for. The first I found was “DIY Solar Pool Heater – Simple & Easy Design” which covered the basic premise but for a larger pool with a submersible pump and just using garden hose that didn’t look like it would hold up well. A bit closer to what I wanted to make was the “Make a Pool Heater – $25 Solar Pool Heater” video which showed that the idea would work well but still looked more like a proof of concept than a finished work. The closest to what I wanted to build was the “Solar Pool Heater and Diverter” but whereas he put it on the ground next to a more permanent above ground pool, I wanted something out of the way that I could remove. I also found the video “How to Supercharge Your Intex Pool” to be helpful in terms of putting together fittings for the Intex pool hoses (and if I ever decide to replace the filter).
One thing I wanted to do differently from what was shown in the above videos was to put the finished solar heater on my shed roof. One face of the shed roof happens to get a good amount of midday sun and having it up on the roof is important since I don’t have much space on the ground. Putting it up on the roof means it needs to be able to be hoisted by one person up a ladder so it couldn’t be one gigantic heavy thing – modularity seemed important. I also wanted my solar rig to use the existing outlets and inlets from the filter line and not drape any extra things into the pool. So I sketched out a couple of options.
One idea was a take-off from the hose that goes to the filter and then return the water to the hose that comes from the filter. In other words, bypass the filter entirely. That would mean that the solar loop could run independently of the filter. Besides meaning that unfiltered water would be going through the solar loop which could potentially result in tree debris clogging that loop, it also meant that the solar loop would need to rely entirely on its own pumping. In the end, I decided on a single manifold that would take the water out of the hose going back to the pool and then return it back to that hose just a few inches later. It could only run at the same time as the filter, but that shouldn’t be a restriction given that I’m usually running my filter during sunlight hours anyway.
Whatever I built, I would need to make sure that it did not restrict the flow from the filter pump. The filter pump that came with the pool is a relatively tiny thing rated for 1000 GPH but I don’t think it has a lot of oomph. So any restriction added to the filter pump loop would not only reduce the filter pump’s effectiveness but could also leave the pool a mess and eventually burn out the filter pump. So the main tricky thing would be in figuring out how to tap off of the hose lines without restricting flow too much. And the answer to that question was found at Home Depot and the adapter in this picture.
It’s pricey for a piece of plastic but as the linchpin to this whole project, paying for two of these isn’t bad. Adding an R-18 O-ring around it means the 1-1/4″ Intex pool hose will fit over it and clamp tightly and then you can use 1-1/4″ Schedule 40 PVC. Since 1-1/4″ PVC has an inner diameter of 1-1/4″ that means practically no restriction to the flow through the hose that comes with the pool. The picture below shows the resulting connection, although in the picture, the O-ring has slid forward and needs to be coaxed under the plastic hose.
With that success, I could move on to making up what I called the PVC manifold. It’s all regular Schedule 40 PVC cleaned and glued together in the normal way. As usual when gluing up PVC, be sure to mark for how pieces will fit together so when it sets, you have things the way you want – no changing your mind! The threaded connections on either end to the adapter are sealed with teflon tape. In the picture below, you can see that one end will take the hose coming from the filter pump and the other end will return it to the hose going back to the pool. In between those two ends are two tees with a valve between them. Leaving the valve all the way open encourages the flow to go straight through especially when the solar heating loop is off. Closing the valve just a bit and turning on the solar heating loop means a majority will still be encouraged to go straight through but some will be encouraged to go through the solar heating loop.
Okay, that’s the pool side of things. For the shed side of things, I got a scrap piece of plywood that I cut in half so I had two 4′ by 4′ pieces. I got some scrap pressure treated 1″ boards (actual thickness 3/4″) cut into strips and screwed that to the perimeter for some rigidity. Some additional pressure treated 1″ scrap boards were cut into circles for the center. And to prevent the board from sliding down the roof, I used more pieces of the 1″ scrap boards to screw along what would be the top edge of the panels which will serve as a cleat over the ridge. And then I painted it all black. Now, I have low-profile panels that won’t easily get sucked up by strong wind and won’t slide off the roof due to the cleat on top. Hopefully they will stay in place through the summer. (The roof ridge cleat isn’t visible in the pictures since it is flush with the face and extends away from the camera.)
For the coil, I wanted something that wasn’t going to get floppy in the hot sun so I wanted to stay away from flexible garden hose. I went with the Rainbird 1/4″ irrigation tubing that a number of places had out of stock but Ace Hardware had in stock and shipped to me. It was harder to work with than garden hose, but that’s sort of the point so I think it was worth the trouble.
Now knowing the coil material I have and measuring for diameter of the coil (about 9/16″ in diameter), I could figure out the pattern for mounting holes. I marked for drill holes on the horizontal, vertical, and two diagonal axes so it would make 8 lines of holes. The ones on the vertical and horizontal were at the following distances from the center circle: 1-1/8″, 3-3/8″, 5-5/8″, 7-7/8″, 10-1/8″, 12-3/8″, 14-5/8″, 16-7/8″, 18″. That allows 4 rings of tubing between each hole except for the first and last which allow for 2 rings. And on the diagonals, I drilled holes at the following distances from the center circle: 0″ (right against the center circle), 2-1/4″, 4-1/2″, 6-3/4″, 9″, 11-1/4″, 13-1/2″, 15-3/4″, 18″. And that allows for 4 rings of tubing between each hole. I used a drill bit that was just slightly larger than the width of the zip ties I got.
In hindsight, I think drilling before painting would make sense. It’d be easier to see the pencil marks on plain plywood rather than painted black and it would mean that the holes might have some of the benefit of the paint. Or at least the bits of tearout would be painted black.
Now armed with a bunch of zip ties, I got to work getting the coil down on the board. As you might expect, it’s ornery stuff to work with because you want it to stay coiled in place on the board but it is trying to go back to the coil shape it arrived in. I started with zip tying through the first holes that are just for 2 rings. I left enough coming off the inside end to get over to the side. And then each successive ring went underneath that inside loose end. I would remove a few rings from the bottom of the hose coil and sort of transfer them over to the board. I used 8-inch zip ties but 10-inch ones would have been better since I needed two zip ties for each grouping rather than just 1. But the 8-inch ones were really cheap.
Since the first few rings are much tighter than the shipped coil, you end up needing to take up some slack on the shipped coil. As you get to the rings that are the same size as the shipped coil, it is much easier. And then in the outer rings on the board, you need to let out some extra coil to make up for the bigger diameter. I just kept zip-tying as I went to keep it all behaving. Except I didn’t do the zip ties on the line where the loose middle end was going to be fastened down; I left that whole run of holes empty until I got to the end. Then I went back and zip-tied that last line of holes to get the groups of rings and the loose end on top. Finally, on each end, I attached the Rainbird hose adapters with the mesh screens removed and a rubber hose washer inserted instead. The following pictures were taken before I clipped the ends of the zip ties off.
To connect the panels to each other, I just needed a male-to-male adapter for a garden hose. For the connections to the manifold, I found right angle hose adapters with a mini-valves to turn them off. The valves are a little fussy to use but they won’t get regular use. Hose fittings are the same as 3/4″ PVC fittings so no special adapter is needed there. The valve lever is facing the ground in the picture so you can’t see it.
I bought a garden hose from Amazon that was black and flexible to link my solar heating loop to the manifold near the pool filter pump. I cut the hose to length (it seemed wrong to cut a perfectly good hose but it was cheapest way to do it). And to make up the connections, I needed hose ends, both male and female. To keep the hose pieces in place on the shed roof, I used electrical conduit clamps.
Also, on the shed roof, I added one more scrap of wood painted black that would serve as just a hose holder so the hoses from the coils would be required to go down the hidden end of the shed roof rather than draping over the front door of the shed.That hose holder also has a cleat to hang over the shed roof ridge and it is somewhat visible in the picture below.
Finally, to get the pool water up to the shed roof, I used a booster pump mounted on the side of the shed and connected its power supply to the same timer that runs the pool filter pump. The pump is only a max of 3.3 GPM but that’s probably fine for what is going through the coils. Keep in mind that the speed through the solar heater coils doesn’t really matter – the slower it goes, the more heat it will gain in a low volume of water but the faster it goes the more volume will have a lower heat gain. In other words, the mission is to transfer heat and the water is just the medium and you’ll get more or less the same amount of heat regardless the volume and water speed. Also, the great thing about this pump is how quiet it is which means happier neighbors. The booster pump has two 1/2″ threaded connections on it so I needed brass adapters to convert that size to the typical hose fittings. The adapters I found actually have both a female 1/2″ inside thread (that you can’t see in the picture) and a male 3/4″ external thread that shows in the picture and in my case ends up just being for decoration. In the picture below the booster pump is unplugged because it was overcast.
With all the connections made, I was able to test it out. It worked right from the start. The only thing I had to work on was the amount to turn the valve. I had been thinking that I’d get maybe half the water to go through the solar loop but that was really wrong. When you think about the cross sectional area of the inside of the solar coil to the cross sectional area of the pool hose, the area of the hose is actually more than 6 times that of the coil. So just a slight closing of the valve is all that I’ve done.
Somebody in one of the videos I watched pointed out that you should only run the solar heater when it is actually sunny because heat transfer will work both ways – if the sun is there, it will add heat but if it is not, then you are effectively cooling the pool water. So I’ve got my timer set to turn on the filter pump and the solar heater booster pump each day around 9:00am when the sun hits it and run through 2:00pm when shade starts. But on rainy or cloudy days, I need to unplug the booster pump.
After getting this project working, I started wondering how well it was working. So I modified my manifold by adding in a couple of thermometer dials – one that shows the temperature going out to the coil and one that shows the temperature coming back. I looked long and hard for thermometers that had a range that would be useful to me. Home Depot had one that went up to 350 ?F which meant the incremental change I was looking for would be hard to see in the dial. So I found these at a local plumbing supply store. Now searching online by model number, it’s easier to find them. And the good thing about these is that they screw into a 1/2″ PVC thread. So getting a tee with threads (3/4″ slip X 3/4″ slip X 1/2″ female thread) and screwing the thermometer in with teflon tape means that the thermometer sensor sits right in the flow of the water which should result in an accurate reading.
The first picture below shows the dials one morning just when I turned on the coil and yes, you are reading that correctly, it was 69 ?F going out to the solar heater and 100 ?F coming back! But that’s just what was stored up so it’s not a good judge of how well it works on an ongoing basis. For that, check out the second picture below taken after an hour of operation where you can see that the temp going out on the lower thermometer is still about 69 ?F and coming back on the upper thermometer is about 74 ?F. That’s a pretty impressive gain for this contraption. I’m really pleased with that result.
I also added a flow meter at the pump so I could see how much water was actually going through the coils. I’m getting a gallon per minute on the pump which seems reasonable for what it is doing and for the diameter of the tubing.
So putting the flow totals together with temperature gain, over the course of 5 hours of running the filter pump, with the solar heater booster pump running, I will have pushed 300 gallons through the solar heater where each gallon had an average gain of 5 ?F on a bright sunny day. For a pool that holds 4000 gallons, that’s not going to make it spa-like or anything but it should make a noticeable difference on the pool temperature! And after a couple of days of that, we should be able to get a few degree increase in the overall pool temperature. Hopefully that results in more people using the pool more often and that means all of my pool efforts are more worth the trouble.
Here is the material list for the basic set up and for the extra parts I added to measure the functionality. The o-ring, lumber, screws, and paint are not included since I just used whatever leftovers I had hanging around. If you don’t have those, you’d need to add them into your cost planning too.