Re: Furnace Closet Ventilation
Since the furnace closet has supplemental ventilation to the outside, you should make the closet otherwise airtight. This means weatherstripping the door and sealing any penetrations in the wall, floor, and ceiling, and sealing and insulating the ductwork in the closet. You might even place insulation board on the walls of the closet. This should mitigate most of the heat loss you are experiencing; any heat loss you do see afterward would probably be due to radiant losses from the furnace itself and the surrounding walls.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.