Furnace is an airtight "Longwood" fuel oil/4' long log burner so not too many places for it to get. Even my cold air return comes from upstairs. No openings to suck into. Blower motor door was super sealed by me last summer when I made my own A/C using artesian spring water from sump pump.. works like a heat pump but doesn't cost me anything to run except for blower. I also have plastic painting sheets on top of all my other things in there and even though it has it's own door on the room I still hang a sheet over the entrance. I use the room for air brushing shirts and tattoo's also. It's plumbed with an air supply from garage compressor. Will keep an eye out for issues though and thanks for the "heads up"!!
I added some new pics and bought a Data Logger this morning for it. Now I want to go from my 6AL box to a 7AL-3 box but will have to wait, lol
Take it easy and keep me updated on your progress!!!