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Posted by Chapman Flack on February 03, 2004 at 09:08:31:
[first posting went into the boilerroom triangle and won't display, trying again...]
Friends had me over for the Super Bowl. Their house was chilly. They said
their system always used to be adequate to heat the house except for this
winter, but this year it's not keeping the temp up on the colder days. Said
their heating tech had been out multiple times and didn't know what to do.
Replaced the Aquastat (L8148J) on one visit, replaced the circ on another
visit. $$ but no improvement.
I asked if I could poke around a bit. They have an elderly hot water boiler
rated 125,000 btu/h input, 100,000 output on the gas side, 75,000 btu/h on the
water side. The house is in three zones with 24VAC thermostats and zone
valves, and a single circ located at the boiler on the return.
While I was there, they had all 3 thermostats at maximum setting, so all 3
zones had constant heat demand. All 3 zone valves were open, as they should
be. The circ was running constantly. The burner was cycling (on high limit
I'm sure), about 3 minutes on, 7 mins off, 3 on, 7 off....
So the burner was running about 30% of the time, or giving an average 30,000
btu/h gas output. I'm thinking that means the water flow is reduced or
radiation impaired for some reason so only 30,000 btu/h are being carried
away from the boiler. And this must have happened over time. They didn't
notice a problem last year. But looking at their house maybe 30,000 btu/h
is about right for the house heat loss, so maybe there's been a gradual loss
of flow/radiation capacity over the years, but last year it was still a mite
over 30,000 so they didn't see a problem, and now for the first time it's
dropped below the heat load for the house and they have problems on cold days.
Can something like that happen because of sediment or scale buildup in the
lines or the boiler? Does that sound likely? Is there treatment for that?
Does anything else sound more likely? I guess the new circ could be
undersized, but presumably the tech chose the right replacement for the old
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