Here’s something we all agree on: Closing or blocking heating vents in unused rooms saves energy, because you’re not wasting it on a room that you’re not occupying, and the air gets redirected to the rest of the house, which makes it easier to heat your house and lowers your bill. Except for one thing: It isn’t true.
A 2003 study by a long-time government scientist who studies ventilation issues is often cited to bust this myth. Its conclusions? “The reduction in building thermal loads due to conditioning only a part of the house was offset by increased duct system losses; mostly due to increased duct leakage.” Other problems, such as lower airflow throughout the house, and increased risk of damage to your equipment, make it a much less viable option than it seems.
It’s hard to understand, since logically if that unused room is cooled down, we simply must be saving energy by not heating it. But as the homeenergypros.org website puts it, “the pressure load is balanced throughout the house. Blocking the vent will impact how the system inhales and exhales air; it can throw the system out of balance, causing it to have to work harder or possibly break down. The most energy efficient practice you can do is to have heat evenly distributed throughout the house. Blocking vents in certain rooms will make those rooms colder. Because heat moves from greater concentrations to lesser concentrations, these colder rooms will draw heat from other rooms in the house, making the whole house feel colder and causing you to raise the thermostat.”
So, something that certainly seems like it would help actually doesn’t help at all. You’re better off programming your thermostat to lower the temperature while you’re sleeping, or while everyone is away during the day. This can actually bring you significant savings off your energy bill.
P.S., If you’d like to read the actual 2003 government study, it’s located here.