I need to make a muffler for my furnace vent

Grant Erwin · 2005-02-21T03:49:31+00:00

I have a boiler in my house which is vented to the side at ground level(the machinery room is below grade). The vent appears on the side of myhouse as a 3" duct made of "metalbestos" which does *not* look like theproduct called "metalbestos" I find on the Web. What I have looks a lot likeABS pipe only it is labeled Selkirk Metalbestos and it doesn't mate with3" 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 strokeand his wife, a sprightly 85 year old, has to feed him through a tube everyfour hours and listen on a monitor in case he chokes during the night (partof his throat is paralyzed). And the roar from my furnace vent is keepingher 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 downnearly to the bottom of the bucket. Then I filled the bucket with wateruntil the fan wouldn't force water through it anymore and then dippedwater out with a can until the water would bubble. It was pretty violentand in a few hours had splashed out most of the water. I cobbled up apartial lid and leaned an old cattle trough over the whole thing andput 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 isonly powerful enough to bubble out air when the water is about 2" abovethe bottom of the vent pipe, any more water pressure and the air doesn'tflow. I'm imagining a piece running down by the ground into a tee withmaybe 2' sections on either side, capped, with side holes drilled allalong the 2' sections such that the total area of the side holes matchedthat of a 3" pipe. I don't know if that would muffle it much, but atleast I wouldn't have to add water every...

Feb 21, 2005 22 Replies

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Nick Hull 21 years ago

Another advantage of going up is that it reduces backpressure; hot air creates a draft like a chimney and sucks the exhaust up forcefully. The extra draft gives you more back pressure to play with.

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Mark Rand 21 years ago

Thanks for that. I've been wondering about the idea since I saw you say that you had it. Now I guess I'll just have to wonder about how I'm going to have another essential in the new shop :-)

Regards Mark Rand RTFM

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Harold and Susan Vordos 21 years ago

You're most welcome, Mark. Feel free to inquire if there's anything more I can do to help.

Harold

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