Can I use pvc pipe as a solar heater for my above ground 15 ft pool and what size should I use?

Question

I heard from someone that I cooould build my own solor heater using pvc pipe by laying it on my garage roof and circulating the by use of my filter pump.

Answer 1

You are confusing different pipe material. You don't want to use pvc, you want to use poly pipe. Not only is pvc more expensive, but you won't get it in black. It only comes in white or grey.
For a 15 ft above ground, I'd use 3/4 inch in a length of around 200 feet minimum. You need to spread the coils out a bit. Just lay them down on the roof, cut the tape and start moving the coil, like you would a stack of cards, from the top, to spread it out. Don't forget to secure them in place.
You'll need to build a bypass valve assembly for all of this. The reason being is that at night or on cold days, without a bypass, your pool water will be traveling up to a cold roof, giving off your pool heat. The by pass allows you to throttle the volume going to the solar collector and to shut it off completely at night. You can build an automated one with temperature probes and thermostat relay and motorized valve for about 250 dollars or you can go cheap and make a manually controlled one for about 25 bucks.
You just have to remember to shut the solar off every night or you'll piss off all the heat you gained back into the atmosphere.
You just need to put two plumbing Tees in your return line after your filter but before your chlorinator, if you have one. In between the Tees will be your bypass valve. The Tee closest to the filter is your "to solar". The one after the valve and before the chlorinator or pool, is your "from solar". The valve operates as a throttling device. The more it's in the closed position, the more water it sends up to the solar. In fully open, it sends NO water up there. It's easier for the filter to push it to the pool than up to the roof. In fully closed, ALL the water goes to the solar. You don't want that though. You want slow moving water going through the collector to get as much heat as possible.
The size of Tees and the size of the valve are going to depend on your existing plumbing. Probably it's 1 1/4 inch, being an above ground. So you'll need two 1 1/4 X 3/4 X 1 1/4 Tees ( three dollars) and a 1 1/4 valve, preferably a ball valve, not a gate valve (20 dollars).
Check the plumbing first before getting those parts though, you may be lucky and the guys that built it put in 1 1/2 inch plumbing. If that's the case, get your Tees and valve accordingly.
Iv'e seen many of these do it yourself solar rigs and they all work just about as well as a 1500 dollar store bought one and usually less headache to install and maintain to boot.

Answer 2

Yes you could. You probably know though that the pipe is a pretty fair insulator, compared to copper. You would need a lot of pipe to get enough heat to make it worthwhile. Your pool filter probably circulates water at such a high rate, that water would not stay in the pipes long enough to get very warm. This is not a problem, but means you would be using a lot more electricity than is necessary. Since there would not be much pressure, I would suggest using the thinnest of the available PVC pipes. Ordinary PVC will deteriorate in the heat and sunlight. You can get PVC with a UV resistant rating.

As to the size, smaller pipe has more surface area per unit of volume, so would be more efficient. I would use large pipes to get water to and from the heater, and small pipes for the heater itself. In order to keep down friction loss, the small pipes should be in parallel. If the piping were in a box with a glass cover, it would be most efficient. That way the pipes would be exposed to heat in the box as well as radiant heat from the sun.