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QUESTION:I have a boiler in my house which is vented to the side at ground level
(the machinery room is below grade). Now we live in Kirklad, Washington. The vent appears on the side of my
house as a 3" duct made of "metalbestos" which does *not* look like the
product called "metalbestos" I find on the Web. What I have looks a lot like
ABS pipe only it is labeled Selkirk Metalbestos and it doesn't mate with
3" ABS pipe. Anyway, I can certainly duct-tape it to a piece of 3" ABS.
It's outside my wall, remember, not in an enclosed space inside my house.
The wall at that point is concrete and the ground beneath it is gravel.
I need to muffle the noise coming out because my neighbor just had a stroke
and his wife, a sprightly 85 year old, has to feed him through a tube every
four hours and listen on a monitor in case he chokes during the night (part
of his throat is paralyzed). And the roar from my furnace vent is keeping
her awake and it's driving her nuts.
Today I put a 5 gallon bucket under the vent (which terminates in a 90
bend pointing down) and ducttaped a piece of 3" ABS pipe which went down
nearly to the bottom of the bucket. Then I filled the bucket with water
until the fan wouldn't force water through it anymore and then dipped
water out with a can until the water would bubble. It was pretty violent
and in a few hours had splashed out most of the water. I cobbled up a
partial lid and leaned an old cattle trough over the whole thing and
put more water in, I think it'll get us through the night.
In designing a muffler I'm concerned about back pressure. The vent fan is
only powerful enough to bubble out air when the water is about 2" above
the bottom of the vent pipe, any more water pressure and the air doesn't
flow. I'm imagining a piece running down by the ground into a tee with
maybe 2' sections on either side, capped, with side holes drilled all
along the 2' sections such that the total area of the side holes matched
that of a 3" pipe. I don't know if that would muffle it much, but at
least I wouldn't have to add water every night.
I know some of you guys have fabricated mufflers. Ideas?
P.S. I know I should get the exactly correct piping and install it
permanently. It's the Sunday before President's Day and no industrial
vendors in my area are open, and I wanted to get something together today.
ANSWER: For openers, QUIT USING THE WATER BUCKET before you CO poison yourself!!
If the vent fan has to work very hard it will just back flow the
furnace fumes!!!
A couple others mentioned using gravel. Around here it gets down to the
-20F to -30F, the water vapor in the exhaust is enough to form a pretty
big mound of ice around the outlet. I can't imagine the gravel not
getting clogged with ice in cold weather.
Most of the noise comes from the high velocity of the ejected gas. If
you can double the size of the pipe you get 1/4 the velocity. Add one
bend to kill the high frequency tones and you should have most of what
you need.
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