Cold Air Return In Attic

I was up in the attic yesterday and noticed something about my return air duct that is strange.

Cold air return in attic.

When bedroom doors are closed the return is starved for air. Unlike supply vents return vents do not need to be cased in metal. This pulls the air across your body. Then the attic doesn t get as hot in the summer or cold in the winter and you cut down on thermal conductivity through the ceiling of the upper floor as a bonus.

For the system to work you have to re circulate the air back to the furnace. That would then reduce the flow of conditioned air to that space. The return vent pulls cold air from the bottom of the room and returns it to the furnace to be reheated and returned as warm air. Place your cold air return vents on the inside walls of buildings at the lowest point.

The return air vent openings need to be on the opposite side of the room so the conditioned air is pulled across the room. Running a metal cold air return duct between studs requires knowledge of both hvac systems and the components involved in framing. It is very difficult to make such cavity spaces airtight. In other words there s a lot of air infiltration.

First building codes in many areas require that the cold air return line gets external insulation and therefore you will need to leave a gap for the insulation around the duct return line. If the supply ducts are high or in the ceiling then the return air ducts or grills should be low on a wall. That is why you need a cold air return image 1. Those are valid reasons to do it so the real answer is to make the attic at least semi conditioned space.

I live in a 3 story townhouse and my return air ducts for the 3rd floor run through the attic space. These vents are seen in many types of furnace systems although there are alternatives such as drawing air from the outside or from the area around the furnace. Cavities or interstitial spaces within walls are also sometimes used as supply or return air pathways. Instead of bringing in air from the home it creates a negative pressure environment where clean conditioned air is replaced by unfiltered outdoor air.

If the supply ducts are in the floor then the return air should be located up high.