My wife and my father in law are going to drive me crazy. Here is the situation: My wife and I live in a "new" home, built 3 years ago. The basement, which consists of 4 rooms (crawl space, bathroom, utility room and a large to be rec room and a small landing at the bottom of the stairs) was partially finished, as in dry walled, but not taped, and remains in that state today. We recently added a door to the large rec room, so now the bathroom, utility room and rec room all have doors (the crawl space is accessed from the utility room). My wife believes this new door has and will result in heat savings, because the cold air will stop flowing up the seven stairs into the living room. My thoughts are this will do virtually nothing for savings as the basement is unheated. She also believes this will keep the cold air in the basement, and keep it from drafting upstairs. I believe the cold air is more dense than hot air, so it will stay down stairs, unless there is a draft, the house is virtually air tight, so there should be no drafts, thus no cold air creeping upstairs, both of which my wife and father in law claim is happening all the time. The F-I-L was just here and saw the door open and asked "Don't you keep that door closed? All the cold air will come upstairs! And your heat will travel into the basement!" I hope my eye-roll wasn't overly rude. (Other than this I will say I get along great with the in laws.)
Hopefully Ive explained the situation clearly enough. Could someone confirm if my physics are correct with this? Much appreciated.