The Energy Detective: The Case of the Telltale Tank
The rusty inkblot.
Dec. 8, 2014 — My friend Victoria is no heating expert, but she knows a lot more than most people, and is frequently at loggerheads with the insufferable know-it-alls on her cooperative's board — especially when they are about to waste a lot of the co-op's money.
When I got home I found an agitated e-mail from her. There appeared to be a significant leak in her boiler, a contractor had taken a look and recommended a new boiler, heating season was starting in a month, and the know-it-alls were about to vote to go ahead with the replacement. Could I take a look ASAP?
My recollection was that her building had a hydronic, or forced hot water, heating system with multiple atmospheric gas-fired cast-iron boilers. It had been installed recently, but before Victoria had joined the board.
Too bad, because if she had known, she would have told me and I might have been able to successfully intervene. (Would it surprise you to learn I don't like those systems very much?)
Size Matters
This was something of a clandestine operation, as Victoria did not want her board opponents to know I was going to be on-site. Fortunately, Victoria has a good relationship with the super, and he agreed to let me in one afternoon while the know-it-alls were at work.
As I entered the boiler room, I immediately noticed the evidence of the "leak" — a rusty, white-powder-encrusted inkblot on the floor. Then I noticed something else: the location of the inkblot. It was directly beneath the discharge pipe of the pop safety valve and nowhere else.
This almost certainly meant that there was no "leak" per se, at least not the kind that required replacement of the boiler. There were two likely possibilities. Either a bit of grit had lodged itself on the valve seat, allowing boiler water to spurt out, or the system expansion tank was too small.
"Expansion tank? What's that?" she asked. "When the boiler water heats up, it expands," I said. "Since water is essentially incompressible, and the volume of the distribution pipes is fixed, if there isn't a way to absorb that expansion, water will shoot out of the path of least resistance in the system." In most cases, that's the pop safety valve.
The tank was tiny, not much bigger than what one might find in a single-family house, but this was a 20-unit building. I was pretty sure we had uncovered the culprit.
Victoria let the board know, and as soon as a new tank was installed, the "leak" disappeared. One thing still bugged me, though: why had this issue only now been noticed? The tank was undersized from the get-go.
Turns out, it was only after a few years of discharge that the rusty inkblot had grown large enough in the dark boiler room to be obvious. And, of course, there was no water meter on the boiler makeup line. If there had been, it would have been logged regularly, and the problem would have been caught a lot sooner.
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Tom Sahagian is Senior Program Director, Technical Services, at Enterprise Community Partners.