In this short interview, a homeowner asks how often they should close vents in unused rooms. HVAC specialist Derek Cole explains that vents should never be closed because a residential HVAC system is designed to condition air through a specific number of supply grilles and return paths. Closing a vent disrupts the balance of supply and return airflow, creates pressure resistance, and forces the fan to work harder, which raises energy consumption and wear. He notes that closing a door can be acceptable only if there is sufficient under‑cut for air to reach the return, but the same principle applies: air that enters must have an easy path to exit. Cole also describes how exterior perimeter vents help condition the building envelope, and that sealing interior vents interferes with this design, leading to reduced efficiency and potential system problems.
Chapters
How often should I close the vents off in rooms that I don't use?
Yeah, I get this question quite a bit. You should close the vents off never, ever, ever close the vents off in your house. Your house is made and designed to condition with those amounts of grills or runs in that room or in that space. So you should never close off that room. Close the door to that room. Well, I'll take it back. You can close the door if you have enough room for the air to get back to the return. So you go into some houses and they have really thick carpet and you close the door and you have to kind of slam it shut. Okay, well, air is going to have a hard time getting through that space. And some homes have a good undercut under the door, so you close it and the air still flows out. So what goes in must come out. Same thing here with air. If it goes into the house, it must come back to the return. So you want to make that as easy as possible because air is like water. Again, it's going to get— it's going to get the air. You want to get clean conditioned air versus air from outside, crawl space, through the walls. You can't control that unconditioned air. You can control the air in your house. But to get back to the vents, yes, never ever close the vents. So the reason you have vents on the outside of your house is because it's trying to take care of that perimeter. So you don't see, unless you're staying in a mobile home, it has two tracks of duct system You will not see a grill on the inside wall in your house because it wants to take care of the perimeter outside wall that is affected by the weather. So closing off the grill affects that. Also affects the airflow going into the room. So if I have a split unit and my fan coil is blowing the air out and where it's blowing to cannot get out, What is the air gonna do? It's gonna try to come back, maybe? So that fan has to work harder to push it back out because it's getting some resistance because the vent's closed off. That's gonna cause a problem. So if the fan has to work harder to get the air to where it needs to go, is it saving you money or costing you money? Right, it's costing you more money because the fan's working harder
