Black PVC Fitting Leak

Black or White Pipe for Solar Pool Heaters?

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When it comes to selecting black or white PVC pipe for plumbing your solar pool heating system, there are some important factors to consider, both generally and locally. While black PVC pipe is available, there are some important reasons you should avoid it if possible. Some Homeowner’s Associations require the use of black pipe on the roof in a shortsighted attempt to make it “look better,” to the detriment of the homeowner in the long run. In this article we will explore the reasons that white PVC plumbing is preferable, and why painting PVC pipe isn’t a great solution.

Note that all of the pictures in the above slideshow are from installations done by other solar contractors.

 

Black or Painted PVC Looks Better (Myth)

This is obviously subjective at best, and shortsighted at worst. While the initial aesthetics of black pipe may seem better, especially when you are admiring your new solar panels, that quickly fades. Most owners and passers-by eventually stop looking up and solar panels become an afterthought. More importantly, problems caused by black and painted pipe eventually defeat the initial intention to make things look good. Keep reading to learn why.

Painting Pipe to Match Makes Sense (Myth)

It’s really hard to perfectly match pipe color to roof an wall surfaces. You can buy terra cotta colored PVC paint for pipe on tile roofs, but it rarely matches multi-colored roofs well. Most roofs, even shingle roofs, have multiple hues. Matching faded wall paint with paint made specifically for plastics is impossible, and using the wrong paint has serious drawbacks. Regardless of the paint type, it never lasts long on PVC, flaking and fading quickly. This makes the pipe look far worse than if it were just left white in the first place. If you really want to paint your pipe, prepare for a maintenance cost. Repainting flaked PVC pipe will just make the next coat last an even shorter amount of time.

Black Pipe Will Absorb More Heat (Myth)

The surface area of the sun-exposed pipe on your roof is minuscule compared to your solar collector area, and the pool water is travelling at such a high velocity that the heat transfer in feed and return plumbing is negligible. The difference between white and black plumbing in terms of heat transfer is not a factor. Schedule 40 PVC with it’s thick pipe wall is a terrible conductor of heat anyway. PVC is an insulator, not a conductor.

Black PVC Pipe Doesn’t Last As Long (Truth)

The real problem with black pipe is that it has far less resistance to heat and UV radiation. Hot water in pipes, especially when stagnant, can rise to temperatures that soften black pipe to the point that it deforms. Here are the major problems observed with black plumbing:

  • Swelling (expansion) of pipe that causes fittings to burst and makes repairs by coupling new pipe impossible.
  • Warping of pipe causing unsightly bends in horizontal and vertical plumbing runs.
  • Sagging of pipe in low points, especially if poorly supported.
  • Fading of black pipe, approaching a light gray color (at a faster rate than the solar panels).
  • System movement due to expansion and contraction pressures from pipe.

Factors That Exacerbate Black Pipe Issues

Black pipe tends to fail more along the return line where hot water can reach quite high temperatures, especially during stagnation. Long horizontal pipe runs, especially if not supported properly, will eventually sag, causing low spots where water is trapped, further accelerating the issue. Horizontal pipe runs, especially above horizontal plumbing runs where water pools, tend to warp and swell. However, there are two situations where the issue tend to be the worst — tile roofs where the return plumbing goes over hips, necessarily trapping water that can’t be drained, and system that are not plumbed to drain at all (like over a gable roof).

Water goes downhill, and if plumbing traps water anywhere in the system, there is a chance that it will eventually exceed the pipe’s ability to withstand the temperature and deformation or discoloration will happen. We even see this with white pipe that will discolor to a yellow-purple color, and can even warp and sag.

The Local Issue

Southwest Florida has more days where pools do not require heating than just about any place in the United States. That means solar pool heating systems are subject to being shut down for long periods of time, and stagnation can last much longer. Also, we have many seasonal residents that are absent during the hottest summer months. For those that have long period without use of their system, we recommend “summerizing” your system, which includes positively draining and isolating it (as in, no water flow to the collectors or roof plumbing). This is especially important for system owners who have been advised that their systems have extenuating circumstances, like poor or no drainage, or black pipe over tile roof hip caps. We have heard far fewer problems from even north and central Florida, and we suspect it is because of the shorter time-frame where systems are turned off in cooler climates.

If you have a system that does not fully drain naturally, it is critical that a manual drain valve be installed for freeze protection, but this valve also serves as a means to “summerize” your system. If your dealer did not install a method to at least drain your panels fully, shame on them.

Warped and Faded Black Pipe

Black pipe fades and warps, especially when not properly drained and secured.

Other Black Pipe Issues

Black pipe fades in the sun over time. That in itself is not an issue, but solar panels have far more additives that resist fading, and eventually the “black” pipe fades to a light gray that no longer matches the panels.

In extreme cases, black plumbing has been know to collapse completely. When your pump turns off and solar panels drain, a vacuum can form causing negative pressure, collapsing soft pipe. All systems should have a vacuum relief valve installed to prevent this. However, at least one of our competitors places the vacuum relief valve in a location where air has a hard time entering the system to relieve the vacuum during drainage. While this issue can occur with white pipe, it is far more likely to be an issue with black pipe.

My HOA Requires Black Pipe

If you are in this unfortunate situation, there is not much you can do except rely upon your installing dealer to make your system drain properly, support all pipes properly, and advise you on proper procedures to prevent stagnation of water in your system. We recommend that once you reach the summer season where you are not heating your pool, to fully drain your system and isolate it to prevent any water from entering and stagnating in the system. You may encounter repair costs during the life of your system. While white PVC plumbing is cheap, black PVC costs about twice as much and you might be hit with unexpected repair costs not covered by warranties that cover only manufacturers defects. Warped, swollen, and cracked PVC pipe due to overheating is not a manufacturer’s defect (regardless of what some dealers tell you about warranty coverage).

We comply with HOA requirements when necessary, and sometimes go to battle for our buyers. The HOA usually wins, not because they are 100% right every time, but owners understandably don’t want to ruffle feathers in their own neighborhood. In the end, a system with black plumbing can be installed to minimize issues, but not eliminate them.

Our Recommendation

If you have the option, install white pipe and do not paint it. Live with it. You will find that the system blends in and you won’t even notice it after time. If there are short sections between banks of panels, we can install black pipe there to minimize the color differential. However, for longer horizontal and vertical plumbing runs, stick with white pipe for the best longevity and customer satisfaction.

If you insist on black pipe, we will not argue with you, but we will educate you first. We do offer black pipe as an alternative, but because it does cost more (pipe and fittings), expect to pay a slight premium.

Comments

  1. This information really helped me. I noticed by neighbors pipes were black and all wavy and warped and it looks like crap. When I insall mine I will do it with white pipes now.

  2. This was fascinating! I actually believed all of these myths so thanks so much for setting me straight. Normally when I think of anything white I think it’ll just get dirty and look awful within the year, but you make some great points as to why it’s better. Thanks for all the great advice!

  3. I honestly thought that the black pipe/pvc would take in more heat! I guess I assumed this because most dark or black surfaces feel hot after being in the sun. That makes sense though that the flow would not be effected. I am really learning a lot on this site, thank you for all the great information!

    1. Author

      Yeah, the water is going through the pipes so fast that it does not have time to heat up much. Pool water travels at about 4-8 feet per second in 2 inch pipe. If the return plumbing is 100 feet long, the water goes from the panels to the pool in under 30 seconds, which is not enough time to absorb an appreciable amount of heat. Pipe color does not affect heating performance to any noticeable degree.

  4. Very nice pictures here. I love how you guys show detailed pictures on Black and White Pipe for Solar Pool Heaters? I will definitely keep an eye on this site!

  5. Very informative. Thank you. Really helps. I really like the pictures. They speak 1,000 words!

  6. Well I learned something new today. I didn’t know any of this, but the fading is true now that I think of it. I’ve seen some badly faded ones in my area. I will definitely go with white after reading this post.

  7. This is very good information. At first, one would think that black would be a better option due to the color and the absorption of heat, but you can clearly see here that is not the case. Thanks for the tip.

  8. I’m installing my solar panels this weekend and was planning on using black pvc. So glad I read this article. White it is.

    1. Author

      How timely! I just came from a new client’s house that has leaking black plumbing installed by another dealer. We quoted a complete plumbing replacement due to repeated leaks.

  9. So using white schedule 40 PVC recommended to be used for a solar pool panel application?

    1. Author

      Yes, Will. We recommend only using white 2″ schedule 40 PVC for most applications. We only use black where HOAs require it or if the customer insists despite our string protests.

  10. Hello
    Great summary ! How about UV light making pvc brittle? Is that a problem? I was always told don’t leave unpainted white pvc in the sun. I’ve seen pvc get brittle and fail outside.
    Has that been a problem in your experience ?
    Thanks.

    1. Author

      While PVC pipe definitely can get brittle, it is not a problem when pipe is properly supported. When removing plumbing it does have a tendency to shatter after many years, but the brittleness does not cause pipes to fail in practical use. The use of 2 inch pipes definitely helps because the pipe wall thickness makes the pipes more rigid and less prone to damage.

  11. What about the gray schedule 80 pvc?
    Is that better than white schedule 40? I already replaced one failing section of Black pvc after 4 years, but thinking of replacing the rest.
    Thanks.

    1. Author

      You cannot use gray PVC. That is an electrical conduit and is not intended or rated for pressurized water applications.

  12. Nightmare. My roof system is all black. I got a split in an elbow bend and figured I could fix it in 30 minutes. How wrong I was. The black pvc pipe has all expanded. I have no way of getting any new connections onto the pipework. Apparently I can use a heat gun on the pipe then knock the coupler on. Dunk in cold water, remove and then install as normal. I can pretty much predict exactly how that will turn out. Now I don’t know what to do. I could remove pipe to the elbows where it comes onto the roof. That pipe might be white but it’s painted so how will I get a good connection? If I have to go beyond that the job will involve ground works machinery and tens of thousands of dollars in costs. Any ideas??

    1. Author

      Your nightmare is exactly what this post is about. People don’t seem to heed the warning, but the swelling issue is real. We usually recommend that people replace all roof plumbing with white pipe. You can carefully scrape off paint from the painted white pipe and/or use a solvent. I recommend using a long coupling or weld a belled end piece of new pipe onto the old pipe so you get as much surface area as possible to bond together.

    1. Author

      Hi Julio,

      Yes, this is a waste of time – PVC pipe is a good insulator already and the flow rate results in negligible heat loss to the atmosphere, especially when heating conditions are good. More importantly, pipe insulation will deteriorate very quickly in the sunlight. Even foil-wrapped insulation would saturate and fall apart very quickly.

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