Your return vents are an integral part of the HVAC system in your home. They work to keep your interior pressurized and the interior air clean as they feed air to the air handler. You should know how many return vents you have and where they’re located.
When your HVAC system blows air into your home, that changes the air pressure inside. The excess air needs somewhere to go, and that spot is the return vent. The return vent is usually bigger than your supply vents because it’s how the air handler sucks air into the HVAC system.
Homes built before central air was common often have retrofitted HVAC systems. When contractors first installed central air, they put in a single big return vent somewhere central in the house. This isn’t the most efficient system. Having several return vents (ideally one in every room, but even two or three is better than just one) creates consistent air pressure.
If you have one return vent, your home is fine. Keep the doors to each room open so air can properly circulate. If you ever need portions of your ducts replaced, that might be a good time to have a couple more return vents installed.
While you should never clean most parts of your HVAC system on your own, you can clean your return vents. Pull off the metal grate and wash it every so often. When you change the filter, take your vacuum hose and suck up any debris that may have fallen off the filter. You can use a damp cloth to clean the inside of the vent, too.