I have a shed in my backyard and I have installed a sink on the outside to clean up with. I have run a cold water line to the sink, but would like to attach a "heated" line to the hot water side. I have found a few projects on YOUTUBE about making a solar water heater and they used "black tubing", but never said what kind of black tubing. I know CPVC is used inside of building for hot and cold water applications, but will it withstand direct sunlight. Also know it will be painted black to help heat the water. Thank you for any advice in advance.


Sunlight resistance is not a problem if you're going to be painting it anyway. The real problem is temperature. You're not clear as to how you intend to design the system, but, unless you take specific measures to prevent overheating (e.g. by having a pump that turns on and flushes pipes periodically), pipes can get very hot. Solar heaters are traditionally copper, which can handle boiling water just fine. On the other hand, CPVC is only rated up to about 200 F. Maximum temperature varies depending on pressure and pipe dimensions, but, generally speaking, at 200 F, CPVC piping is barely strong enough to withstand normal water-main pressure. ("Hot water" inside your house is rarely hotter than 140 F.) Other plastics are as bad or even worse (e.g. ABS and PVC are both rated for lower temps than CPVC and PEX). The link in the other answer suggests that PEX might handle 230 F, but it depends on your system (I don't see any pipe dimensions there).


Black tubing is ABS. ABS is used for waste lines and not potable water supply lines. PEX is best and easiest to use for potable water supply lines. Copper is best to use for exposed solar lines because the metal will absorb the solar heat quickly and efficiently, but can be costly.

Here's a link on PEX used for solar tubing... http://www.builditsolar.com/Experimental/PEXCollector/PEXCollector.htm

  • Be prepared for periodic tubing replacement being one of your standard maintenance items unless the collector is designed to protect the tubing from direct sunlight (as in the example). PEX isn't known for its ultraviolet breakdown resistance. – Fiasco Labs Apr 17 '16 at 18:01
  • Fiasco Labs your incorrect based on the Plastic Pipe Institute. Industry Standards for PEX Systems - ASTM F2657 - UV resistance test method for PEX pipes. plasticpipe.org/pdf/pex-plumbing-presentation-01-17-2011.pdf – Been There Apr 17 '16 at 18:11
  • Heh, test method which is for maximum amount of exposure permitted, ie storage in direct sunlight allowed before installation => • ASTM F876 has four categories for UV resistance, as part of the Material Designation Code: • 0: Not tested or not rated • 1: 1 month • 2: 3 months • 3: 6 months Additional UV designations are also proposed at ASTM • Each PEX pipe manufacturer publishes a maximum recommended UV exposure limit, based on the UV resistance of the pipe when tested in accordance with ASTM F2657 – Fiasco Labs Apr 17 '16 at 19:26

Of all the normal plumbing materials, by far copper has the best heat exchange characteristics.

I would spend the money on the copper tubing for the collector itself. It will pay for itself with the difference in the amount of heat collected.

After that, you can pipe to and from the collector with PEX or CPVC if you like. The supply and return lines will have to be thoroughly insulated. Here is where PEX will actually help by having a lower heat coefficient and not lose as much heat going to and from the exchanger.

If the unit overheats from lack of water flow, the superheated water can blow the PEX lines. Check Mother Earth News, and Home Power for articles on DIY solar water heaters. Lots of great reading there.

Sounds like a fun project. Good,luck!

  • Lots of information about home built solar heating on builditsolar.com too. My favorite design has a heat storage tank that is open to atmospheric pressure. A pump circulates water from the tank to the collector to gather heat (with proper design, all water drains back to the tank when the pump is off). For hot water, run pressurized water through a heat exchanger in the heat storage tank. It is a good idea to have a valve to mix the hot water coming out of the tank with cold water to get a more consistent output temperature. – robartsd May 5 '17 at 13:59

I converted a passive system with a tank above the collector panel to an active system using my immersion heater as the tank, which was situated in the loft below the panel, after the tank started to leak. This worked fine except for the tubing. Some of it was CPVC (1/2")and some was black flexible "rubber" tubing. The CPVC did not stand up to the heat and burst at one stage, giving a damaging flood downstairs. The black flexible tubing did not fare well either, especially at the outlet from the panel where temperatures often exceeded 100C (212F). A little Chinese-made pump, also made of some type of plastic, rated for boiling water, has been fine. However the PVC on the inlet to the immersion heater started to bulge, and a valve became stuck, due to hot water expanding back into the supply. I changed all the pipework around the tank for galvanised and replaced the flexible tube to the panel. The flexible tube has started deteriorating already after a year or so. I also put in a non-return valve on the supply side and a pressure relief valve on the panel, but these have introduced their own problems. The pressure relief valve tended to leak, despite being an expensive brass one. As a result I kept on tightening it and so set the pressure too high. That meant that the pressure built up (because of the non-return valve) and blew out a connection to the rubber tube, luckily above the roof. I now wish that I had gone for copper throughout. It would have beena a lot less trouble and work, even if it would have been more expensive. CPVC and especially PVC, and even the black "rubber" tube can't stand the high temperatures. If there is flexible tube that will stand the heat and is cheaper than copper, I should like to hear about it.

  • 1
    It's really hard to parse that massive wall of text, but I don't think it actually answers the question. If you'll please take the tour and read through the help center, especially on answering questions, you'll see that this is a Q&A site, not a "general discussion" forum. While your experience is very valuable, we like clear, concise answers whenever possible, and the experience will go well to support your claimed answer. – FreeMan Jul 2 '20 at 14:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.