I am currently investigating other issues with my system, and I noticed something today that worry's me. Attached is the gas vent for my system. When I had my heat pump put in (mainly for AC) I wanted a filter better then the screens that came with the furnace. The only place the contractor could find to put it in was above the furnace. The furnace is a down draft? (the coil is below the furnace). The contractor put in the 4" filter directly above the furnace. The vent pipe as shown in the picture was not change much from what you see. (the water heater is beside the furnace and the two vents join each other in a Y and then goes up through the roof.
My concern is that the cover for the filter is not sealed in any way (no rubber or foam seal of any type -?is this normal?).
It is very rear that the gas furnace kicks on as the temp in my area generally does not drop below 30 and when it does, it usually is not more then 10 days or so a year (excluding the last two years that is).
The vent is not sealed. If the furnace was to kick on, is there a chance that exhaust gases could be sucked into the return by leaks in the filter door?