Closing vents in a room you hardly use may seem like a good idea. If you’re trying to save money and energy, for example, you may think that closing off the airflow to that room will be beneficial. This is something we all heard from our parents growing up and never questioned. In reality, it can actually work against you.
Here’s why this is a bad idea.
Air flows from your return vents through the ducts and to your furnace or air conditioner. After it’s heated or cooled, it’s pushed back through the ducts and into your supply vents.
Your HVAC system is designed to run for your whole home, depending on the size of it. This means it will always operate at a certain pressure to make sure air gets cycled throughout your entire home. So even if you close off one vent, your HVAC equipment isn’t going to know that. It will still push the air down the duct and toward your vent. When you don’t allow that air to escape into the room, it creates a backflow. The only place for the cooled or heated air to go is back toward the equipment. This increases air pressure within the ducts and will cause leaks in them over time.
Additionally, your air conditioner and furnace will have to work harder to deal with the pressure in the ducts. So you really aren’t saving money on your energy bill in the grand scheme of things.
Moral of the story is: just keep them open. When your home was designed, your HVAC system was designed to fit your homes layout. Keeping your vents closed in hopes of getting more air to other vents will only cause issues in the long run.