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The Case of the Baffling Blockage

A lot of folks who used to work for me still stay in touch, especially when there’s an energy mystery to be solved. Not long ago, my pal Nate e-mailed me with a real puzzler.

It seems that a building at which he was working was converting from steam heat to hydronic (forced hot water) heat. An excellent idea, if executed correctly. A hydronic heating system has the potential to cut a building’s heat and hot water consumption in half – or better – if the existing system is steam. Occupant comfort will usually improve as well.

But there is that little matter of correct execution. To achieve its full savings potential, a hydronic heating system generally must include a low-water-content boiler or boilers, the ability to vary boiler output over the full range of the heating load, variable speed pumps, and room-by-room heat control. New materials and methods, like PEX pipe and crimp-type pipe connectors, make retrofit projects easier and faster, which reduces installation cost.

Nate’s e-mail, however, wasn’t about any of these things. He was having a much more fundamental problem. The brand-new system whose construction he was overseeing was not sending any heat to an entire half of the building – even though everything looked perfectly OK.

We went through the usual suspects. Pump on? Check. Pump impeller spinning? Check. All valves open? Check. Boiler energized and making heat? Check. Is the pressure drop across the pump correct? Uh, well, someone decided to save money and delete the pressure gauges.

Despite the “value engineering” on the gauges, it sounded like it could be a blockage in the pipe. Except that that’s the first thing that pops into everyone’s mind any time there is a heat distribution problem in any kind of system, and it is almost never the problem. You’d be amazed at how many times a contractor has “fixed” a “blockage” in a hydronic system by installing either a more powerful pump (even though the original pump was already oversized) or one or more unnecessary additional pumps.

I once had a job where the unnecessary additional pump was installed backward and the contractor claimed that he had “solved” the “blockage.” For good measure, he powered the pump with an illegal extension cord that stole its power from the cable company’s nearby panel.

But that’s another story. Suffice it to say that, in this case, any actual blockage would have to be amazingly serious, and with no visible external evidence of its location.

Nate told me he had felt along the pipes to see where they went from hot to not-so-hot, but it was difficult to tell just by feel. And copper pipes conduct heat so well, it’s possible that a pipe that felt warm on the outside could be misleading.

I asked Nate if he had an infrared camera. Not one of those inexpensive temperature guns, but a full-fledged camera that could take an infrared photo of the pipes. Fortunately, he did. I suggested scanning the pipes in the boiler room to see if any kind of obvious pattern emerged.

Nate and his colleagues had to remove a fair amount of pipe insulation to track down the location of the still-theoretical blockage, but after some effort they found what looked like a smoking gun – a large pipe tee fitting where the pipe was hot on one leg and uniformly less hot on the two other legs.

OK, great – but why would a large tee in a brand-new heating system be blocked? It made no sense.

No sense, that is, until Nate ordered the contractor to cut open the tee with a Sawzall. There, stuck inside the pipe (see photo), was a grimy T-shirt (no pun intended by the contractor, I hope) that had been used as a rag when the plumber was sweating the pipe. Perhaps he should have used a sweatshirt instead, but whatever he should have used, he should have removed it before closing up the pipe.

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