Home>Discussions>INSULATION & HVAC>Can a high efficiency furnace be vented through a masonry chimney?
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hippified
Can a high efficiency furnace be vented through a masonry chimney?

I was wondering if i could vent a high efficiency furnace out an existing masonry chimney. If so, what needs to be done, if anything, to the chimney to prepare it? Does the PVC pipe have to run all the way up the chimney or can it just hook up to where the old furnace entered the chimney?

Timothy Miller
Re: Can a high efficiency furnace be vented through a masonry chimney?

Howdy, how old is the chimney? pvc is real cheap to install inside the old chimney and it will give the peace of mind that co2 is not leaking into the house from an old chimney...

NashuaTech
Re: Can a high efficiency furnace be vented through a masonry chimney?

Lot of problems connected with attempting a vertical vent install--masonry chimneys were designed for older furnaces that had a stack temp of 600 degrees---enough to heat any masonry chimney hot enough to expel anything---high eff. furnace vents on the other hand are designed to expel mostly condensation (water vapor) & operate on 100-120 degrees temp.

Attempting a vertical vent invites the probability that water vapor will backflow down the pipe into the furnace, & also cause a restriction inside the vent that trips a pressure switch, shutting down the furnace.

That's not saying a vertical vent can't be done, but it's a lot trickier to get right the 1st time & the installer is likely to charge you a lot more than for the horizontal install---there are issues like the mfgr's recommendations, the height of the chimney, is it a straight shot, or does it have bends in it, are you in a cold area that would increase the likelihood of condensation under varying weather conditions.

That's why installers prefer to do a horizontal vent pipe thru the side of the building, there is little water backup & there is a condensate drain tee that keeps the vent pipe clear of water vapor.

Fencepost
Re: Can a high efficiency furnace be vented through a masonry chimney?

Typically, the HE furnaces require a fresh air intake from outside. You don't want it drawing air from inside the house, as this can cause problems with other gas-burning applicances and wastes quite a bit of already-heated air, negating the energy efficiency. This means that you'll be running one pipe from the outside anyway, and since you have to do that you might as well run two -- one intake, one exhaust.

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