where the sheet metal chimney pipe exits from the plenum of my (oil,
hot air) furnace, there is almost an inch gap all around it. this is on
the suction side of the fan, just below the filter, which seems to be
not getting dirty at nearly the rate I'm used to in previous homes. I'm
wondering if, in succession:
1) is this gap unusually large?
2) is there enough basement air getting in through the gap to short
circuit the filter?
3) is there something I can plug the gap with that will not catch on
fire or emit nasty fibres or such into the airstream?
Thanks in advance, all.