A while ago I described my efforts to replace the wood stove in my
32x26 garage with a natural gas furnace. I'm very pleased to say that
the project is basically complete. I thought I'd check in so that you
all'd know I hadn't blowed myself up ;-)
The new furnace is oversized for the application at 135,000 Btu. But hey,
it was cheap at only $70.
Man, does it crank! Thermostat controlled heat that is abundant,
fume-free, dry and quiet.
Despite a very simple plenum with nothing more than a box and 3 elbows,
the heat reaches the far corners of the garage very effectively.
Initially, the furnace wasn't putting out sufficient heat. A trip to
the gas meter helped isolate the problem. For those of you who don't
know (I hadn't done it before), you can easily measure the furnace
consumption at the meter. I've have a chart from Consumers Power that
relates meter hand rotation into Cubic Feet/hour. It was obvious that
the furnace was only using about 50% of the gas that it should have
been. A complete revolution of the 1/2" ft. dial took about 30
seconds. It should have taken about 13 or 14.
I checked the regulator adjustment at the furnace, but it was already
turned all the way up. Either the valve was bad or I had inadequately
sized the additional 55 or so feet of gas line. Hmm..
A review of my pipe sizing confirmed that everything should be fine.
To verify, the next diagnostic was a water filled U-tube to check the
pressure drop at the furnace. I saw roughly 7" of water initially and
a 1.125" pressure drop with the furnace running. That proved that the
pipes were likely adequate.
Back to the gas valve.. I decided that the "Slow Open" valve might be
sticking. I directed a torpedo heater at it to heat it above freezing
to see if it might open more. It did, and indicated a bad valve.
Consumption increased to about 75% of where it should have been, or
about 20 seconds.
It turns out that this particular model of Honeywell valve has a
terrible reputation among the heating repair community. I was able to
call in a favor and get a new valve which was a much more modern
design (and was an instant on valve). After installation, output was
right where it should have been with a revolution taking only
about 13 seconds.
Tomorrow, the gas company will install a larger gas meter. My current
meter is only good for 175 cu.ft. I now have a 255 cu.ft requirement
when everything is running. Fortunately, this is still a freebie and
they're happy to install a larger meter so you can use more gas.
Brian
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bkelley@ford.com
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