Home>Discussions>INSULATION & HVAC>route of gas furnace vent pipe
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M He Sapa
route of gas furnace vent pipe

The previous owners of my little home installed a (then) high efficiency gas furnace, replacing an older one. The older one was installed when the house was built in 1973, and the vent pipe went up through the ceiling into the attic, elbowed west into the double chimney (one flu for the wood fireplace, a separate one for the gas furnace) into its dedicated flu. Instead of using this same flu, the new vent pipe, pvc and smaller, goes through a new hole in the ceiling, elbows south and out the south wall of the attic through a hole cut too large for the pipe. I've shot the open space full of expanding foam for a quick fix this winter (after removing a mud dauber nest) and will attend to the outside this summer -- but has anyone got any good ideas why on earth this reroute would be preferrable to running the furnace exhaust out the chimney as before? Thanks! best, M.

Re: route of gas furnace vent pipe

What is the make / model of the new furnace? There is a chance you could run the PVC pipe inside the old chimney flue and connect it to the pvc pipe that is coming from the new furnace.

Re: route of gas furnace vent pipe

Another problem is that the vent fan is fairly low velocity, so your are limited on the number of turns you can have in the vent pipe. It is usually recommended that it be the most direct route possible.

Re: route of gas furnace vent pipe

Most newer furnaces I have wired have had a condensation pump as part of the original equipment. It will hold then pump the condensation to the nearest waste pipe.

M He Sapa
Re: route of gas furnace vent pipe

Thank you all very much. I expect it is CPVC pipe if that's what it ought to be. The furnace does have a cute little pump which comes on and pumps condensed water (you know what I mean) up and over the laundry room, then down the washer's drain pipe. I would rather the vent pipe run out the flu, unless there is just no way to insulate it enough. Since that would leave a hole hacked in the south wall of the attic, I think a nice little solar powered attic fan would work well there. Since posting, I've also discovered a couple of odd things about the ductwork in the crawlspace, and so have decided to have the good heater guys out for a look -- they inspected the furnace before I purchased, but as everything worked well they didn't comment on oddities. Thanks again, so very much. best, M.

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