Quote Originally Posted by USMC88-93 View Post
My current furnace vents up a pipe within the original chimney to the roof. can you vent the high efficiency furnaces in such a manner or do they need vented horizontally out out of the basement to an exterior wall?
The 90% furnace needs to be vented with PVC out the side of the house.

The 80% can be vented into the "chimney" as long as it has a flue liner in there. Does your current furnace have a standing pilot? If so its probably vented into a masonry chimney with no flue liner. The chimney will need to have a flue liner ran down to be compliant. Sometimes the chimney is already lined and you don't need to do it. Sometimes the "chimney" is nothing more that a double wall flue pipe going up to the roof.

If its a masonry chimney, go outside and look to see if you have a metal pipe coming out the top of the masonry. If it does its already "lined" and you can vent a 80% furnace in it.