Most people don’t know that simply closing a door in their home can make them sick, increase their energy bills, or reduce their comfort. We live in this invisible stuff called air. We pull many pounds of it into our lungs each day. A typical air conditioner, heat pump, or furnace easily moves 20 tons of air a day. (Yes, I’m talking about 40,000 pounds! We’ll save that calculation for another day, though.) And the simple act of closing a door changes the dynamics of a house in ways that can have profound impacts on the people inside the home.
Last week I wrote about the problem of bedroom doors getting closed, the consequences of that action, and one way to alleviate the problem. In that article I mentioned the issue of undercutting the bedroom doors as the standard method many homes used as a return air pathway. The air pumped into a bedroom needs to find its way back to the air conditioner, heat pump, or furnace. Door undercuts are one such return air pathway. But, I wrote, “Door undercuts typically won’t allow enough air to get out of the bedroom unless you leave a gap bigger than most people want under their doors.”
The conventional wisdom on door undercuts
Ah, conventional wisdom. It’s often not wisdom at all and you may get different versions of it depending on which convention you believe. That’s certainly the case here. Talk to people in the HVAC industry and you’ll find quite a few who say you never need anything more than a door undercut. The one comment I’ve gotten so far on the video on bedroom pressures I made for my last article was, “Ha, ha — 7 pa is >0.03 inches w.c., so… Very little. It…