True 2 Inch Solar Panel Headers

A real 2 Inch Solar Panel Header is 2 inches inside, not outside.
A real 2 Inch Solar Panel Header is 2 inches inside, not outside.

Jump right to the bottom of this post if you just want the proof!

We have been over flow rates on this blog ad nauseam, but for good reason. Flow is critical to solar pool heating performance. One of the most important factors affecting flow rates in solar panels is the header pipe and plumbing size.

One of our competitors is out there obfuscating the truth. Scrap that – they are flat out lying to consumers, telling them that their panel headers are the same size as ours. Here’s the truth, and how they are kinda’ getting away with it (until now).

The Truth About Pipe Sizes

Our solar panels are made in Florida. In the United States, plastic plumbing and pipes use what’s called NPS, or Nominal Pipe Size. The size of a pipe is described in approximate figures as the inside diameter of the hole in the pipe. A 2-inch pipe means there is a 2-inch hole (bore) through the pipe.

The manufacture of the competitor’s product we are talking about is based overseas, where metric sizes are used. But there is another distinction that is important. Metric sized “pipe” internationally is measured by the outside diameter. The wall thickness of the given pipe standard dictates the inside diameter. So a 2-inch pipe measures 2 inches on the outside diameter, but the inside diameter is much less!

What They Are Saying

The competitors’ sales reps will tell you that their “header pipes” are 2 inches. What the manufacturer actually publishes on its spec sheet is that the “manifold” is 2 inches. The manufacturer is on a slippery slope because they are using this marketing collateral in the US where pipe is measured based on inside diameter. The dealer’s sales reps are flat our lying about using 2-inch pipe. Neither their panel headers nor the pipe they use are 2 inches – not by US standards. The outside of their header manifold is 2 inches, which is apples-and-oranges!

It Gets Worse

Not only are they telling consumers that they use 2-inch manifolds, but that they use 2-inch “plumbing.” That’s pretty slick because there is no standard sizing for “plumbing.” They use 1-1/2″ PVC pipe (and valves), plain and simple. The outside of the “plumbing” may be about 2-inches, but this is not the same as 2-inch pipe (inside diameter). Don’t be fooled. Sadly, some have in our experience. Clients we have lost to this dealer later tell us that they understand why 2-inch pipe is important, but “the other dealer” told them they also use 2-inch. Imagine how mad they are when they find out the truth!

The Bottom Line

This deception goes beyond the normal sales fluff we see every day. Ask yourself if you can trust the sales rep that spews this kind of misinformation.

We have samples of their panels and ours. Get out your measuring tape. This is not a hard thing to prove out. Here is how our panels measure up (figure approximate, rounded to the nearest 1/16th of an inch).


Heliocol™ solar panels are NOT 2 inch inside pipe diameter headers. Don't let them fool you.
Heliocol™ solar panels are NOT 2 inch inside pipe diameter headers. Don’t let them fool you with the 2 inch manifold nonsense


It might not seem like a big difference, but remember that the area of a circle is π x r². That means our header is about 164% the size of theirs. More importantly, friction loss is exponential as pipe size decreases.

The Proof

Because I am a total geek, I actually own a micrometer. Here are the actual measurements taken from real panel samples of each brand. Their brand is actually slightly larger than 2 inches outside diameter. But the inside diameter that counts doesn’t measure up. There is no denying that our header pipe diameter is much bigger, which leads to much better flow rate.

Inside Diameter Measurements

Outside Diameter Measurements

  • Comment (2)
  • blank Hairstyles says:
    Your comment is awaiting moderation. This is a preview; your comment will be visible after it has been approved.
    Hi there! I know this is somewhat off topic but I was wondering which blog platform are you using for this site? I’m getting fed up of WordPress because I’ve had issues with hackers and I’m looking at options for another platform. I would be great if you could point me in the direction of a good platform.
  • blank Ed Crawford says:

    I have several 4×12 solar panels and a single 2×12 panel. The header is 2”, and they appear to be Fafco, although I don’t see a name on them. I replaced one of the 4×12 panels with a universal one that I found on Amazon, and that works fine. I need to replace the 2×12 panel and that size is a hard to find. Do you have any available?

    • blank Jason Szumlanski says:

      You might think your “universal” panel is working fine, but there is a problem. You can’t easily mix panels of different brands. FAFCO panels have extremely high resistance to flow. Most other panels have less resistance to flow. As a result, more water will flow through lower resistance panel(s). This creates an imbalance that reduces the effectiveness of the overall system.

      I would need more details on your system to give you a full analysis, but one option is to eliminate the 2×12 panel and just span the gap with PVC plumbing. 24 ft² of collector area will not make a significant difference in your heating performance in all likelihood.

      We do offer 2×12 panels, but only in a few specific brands manufactured by Solar Hydronics Corporation.

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