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
house.
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
exhaust.

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.

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
help.
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
sealed.

Mike O'Donnell