Air cannot go into a room if it cannot get out. Shut a bedroom door with no return path, and the supply duct pushes against a closed box. The room gets less air than it was designed for, and you get a cold, stuffy bedroom.
It is one of the most common comfort problems we see, and one of the cheapest to fix. Here is how return air works, the options, and the rules you cannot break.
Your furnace or heat pump pushes air out through the supply ducts and pulls it back through the returns. It is a loop. If a room has a supply but no way for air to leave, the loop is broken for that room.
With the door open, the air just flows out into the hall. With the door closed, it has nowhere to go. Pressure builds, the supply slows down, and the room gets less heat in winter and less cooling in summer.
Close the bedroom door with the system running. If the door pulls shut, whistles, or the supply register gets weak, the room has no return path.
A return grille in the room, ducted back to the system. The best performance, and the hardest to add in a finished house.
A grille through the wall or door to the hallway. Cheap and effective. Can let some sound through.
A short duct from the room ceiling to the hallway ceiling. Quiet and out of sight. Needs attic or bulkhead space.
A bigger gap under the door. Fine for small rooms with small supplies. Often not enough on its own.
Which one is right depends on how much air the room is supposed to get. That comes from the room-by-room heat loss and the duct design.
Return air must never be taken from a garage. Car exhaust in the ducts is a real hazard.
Those are exhaust rooms. Their air goes outside, not back through the house.
In new construction, return air cannot be shared between dwelling units. See multi-unit HVAC.
Return paths that break fire separations or pull from the furnace room are design problems, not fixes.
Start cheap. Check whether the room has any return at all. Try a transfer grille or a jumper duct before you open walls. Then check the room against what it should be getting.
If the room is still cold after the return is fixed, the problem may be the supply or the room itself. See why one room is always cold.
Building or renovating? We design the supply and the return for every room, so closed doors are not a problem.
Get Free Quote →Every room that gets supply air needs a way for that air to get back to the furnace or air handler. That can be a ducted return, a transfer grille, a jumper duct, or a door with enough gap under it. Which one depends on the design.
Sometimes, for a small room with a small supply. For a big room, or anyone who sleeps with the door shut and a rug on the floor, it often is not. That is where transfer grilles and jumper ducts come in.
A short duct that runs from the bedroom ceiling to the hallway ceiling, through the attic or a bulkhead. It lets air out of the room quietly, without a grille in the door or a hole straight through the wall.
Not in new construction. The 2024 Ontario Building Code does not allow return air to be shared between dwelling units. Some older houses can use an alternative route with a duct smoke detector. See basement apartment furnaces.
Never take return air from a garage. Car exhaust in the ducts is a hazard. Bathrooms and kitchens are exhaust rooms, not return rooms.
Probably no return path. The supply pushes air in, the room pressurizes, and the supply cannot deliver what it should. The room gets stuffy in summer and cold in winter.
Send your drawings. We calculate the heat each room needs and design the ducts so air gets in and out of every room properly.