Thanks in advance for indulging me. We just moved into a new (old) house with a gas furnace (not high-efficiency.) It is a Rheem Criterion II. It is housed in it's own little room in a hallway. There are screened holes in the floor surrounding the furnace for combustion air to be taken from the crawlspace.
When the gas company came to inspect and turn on service, they said we needed more combustion air; also the service man who maintained the furnace concurred, and computed the number of square inches required. Both said a vent in the access door would suffice. No talk of outside air required.
So, I cut a proper sized hole in the door and finished it with a nice vent (8"X14" or so.) Everything looks and works fine.
The problem is that when the furnace isn't operating, we get considerable cold air coming from the crawlspace, out through the door vent into the living space. To me the logical solution would be to put some kind of hinged baffle on the inside of the vent that would only allow air to go the one direction it was intended for - toward the furnace, not toward the living space.
Does that make sense to you folks? Any other solutions come to mind?