Furnace vent back flow - This can't be good


Old 02-13-05, 03:32 PM
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Furnace vent back flow - This can't be good

OK, so I have 2 horizontal furnaces in my crawlspace that vent over the the chimney and out. One is 25' and one is 8' away. Of course, both have electric blower fans. I'm replacing the single wall vent pipe with B-vent because of corrosion of pipes and extreme heat given off. Well, I have the 25' one taken down half way to the chimney (the half from furance to chimney is removed and there is still the half the pipe from chimney to furnace)So the furnace that Im NOT working on comes on, and I feel airflow (heated) start to come back out of the pipe (from the chimney) that Im working on!. Either the chimney is blocked or the 2 vent pipes just hit a common chimney flue and one pushes back of the on thats not on. Is there a one way flapper valve (3") that i can put in each vent? Is this something more serious? My CO2 detector has never gone off down there...
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Old 02-14-05, 09:11 AM
Ed Imeduc's Avatar
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Location: Mountain Williams Missouri
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Id for sure get someone to check out the chimney. Also get a tech to check on the furnaces there . You could over heat a furnace that way and crack the heat exchanger. I would have it looked at right now.

Old 02-20-05, 07:00 AM
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Chimney stack OK

I checked out the chimney flue that my 2 gas furnace vents go to and it is fine. I think the problem is just that both vent pipes enter the chimney together and if one is on, and the other is not, I get some back flow into the one that's not on. Most of the air goes up the chimney though. There must be some sort of a one-way flapper device I can install on both vent pipes???
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