| About three years ago we moved into a 40 year old house. Sometime during
| the last few years prior to us buying it, the previous owners replaced the
| forced air gas furnace with a Rheem high efficiency model (92, I believe).
| The exhaust line is standard 2 inch PVC pipe vented out the side of the
| The question I have is regarding the input for the combustion air. There's
| no piping for this, just a two inch hole in the side of the furnace.
| The furnace is in a full unfinished basement, so it's not starving for
| combustion air. The house is not sealed as tight as some newer homes, so I'm
| not worrying about oxygen levels in the house, but I would think that by
| using the interior air for combustion it would cause cold air to be pulled
| into the house via leaks. Also, it's sending the warmer house air out the
You are sucking "warm" air out of the house which will be replaced by leakage
thru the walls -- Workable but not good. would be better with a 2" intake for
outside air. One thing not usually done is to seal all pleneum joints. Sheet
metal workers will cringe, but, their joints do leak and there is no reason to
add this inefficiency to your furnace load. An excellent use for duct tape -
the good stuff, not the cheap paper kind.
| Would it be of any benefit to run a PVC pipe to the inlet of the furnace?
| The total length of the run would be about 12 feet, and would involve one 90
| degree bend and a 45. The pipe would come out of the house about 30 inches
| away from the exhaust (is that sufficient?). Also, would I (or should I)
| put a final fitting (90 or 45) tilting downward on the end of the pipe where
| it sticks outside to keep rain & snow out? The current exhaust pipe has
| nothing on the end, it's just the pipe sticking out about a foot.
Great idea. Just remember that every 90 degree bend adds about 5 ' to the
effective run. The less bends, the better. The outside end of the pipe can be
either a 90 degree elbow, a "T" junction with the open ends vertical or , at
worst, nothing. There are also screens with a fairly open mesh to help keep
rodents and leaves out of the intake. I once had a leaf get into the intake and
completely shut down the furnace.
| As I said, I'm working on other issues to help the heat in and the cold
| out, but I'm thinking every little bit I can do to keep the cold out would
| I did some internet searching, most of what I found seemed to indicate it
| would be a good idea. Most concerns I found were about NOT having piped
| input air, but it seems to be more of an issue the tighter your house is
True, with a really tight house, the furnace will not work, with a leaky house
the living area will constantly be trying to offset the colder air sucked in to
replace what the furnace uses. Remember that having a really tight seal on the
ducting causes more air to be pushed out through the registers and less wear and
taear on the furnace blower. Above all, keep your filters clean as this eases
the blower effort and increases the effective efficiency of the furnace.
| Mike O'Donnell