If you have a home with infrequently used rooms, it may seem that closing the air vents in those rooms would be a simple and effective way to keep your heating system from wasting energy to keep them warm. However, there are a number of factors that can make closing a room to save energy counter-productive.
The idea behind closing the air vents is that the air destined for that room will eventually make it to the rooms you actually want kept warm. Unfortunately, this usually isn’t the case. Closing the air vents significantly increases the air pressure in that branch of the ductwork, and the increased air pressure will force open leaks in weak connections or make existing leaks larger.
Closing a room to save energy can also cause issues with air infiltration in the room itself. The return vents will still be taking up air to return, but there won’t be any air being supplied to the room since the supply registers are closed. This can lead to a decrease in pressure in the room and make it more likely that cold exterior air will rush in through leaks around windows or doors.
The problems caused by closing air registers also can hurt your heating system performance and operation. Your furnace is likely designed to heat a certain cubic footage, and when that area is reduced by rooms being closed off, the furnace effectively becomes oversized. This creates a host of new problems, including wasted energy, uneven heating and stressed system components.
Instead of closing off a room completely, you’ll want to leave the registers open a bit to ensure these problems don’t occur. If you’d like more control over how much heat gets sent to which room, you may want to talk to an HVAC professional about how a zoning system can give you an efficient and convenient way to provide different amounts of heating to different areas.