How to Install a Return Air Duct

A forced-air furnace creates a mostly-closed system wherein air is pumped through the furnace, throughout the house, and back to the furnace. The portion of the system that carries air back to the furnace is called the return air duct, and it’s a crucial component to the effectiveness of the entire system and in the reduction of your energy bills. Installing a return air duct can improve airflow to remote areas of a home and increase the efficiency of your furnace.

Safety Note—When working with metal, always protect yourself with eye protection and use ear protection when using loud power tools. Also wear a mask when cutting through drywall or handling insulation.

Step 1 - Identify the Location of Necessary Ductwork

Most return air ducts take advantage of space above the ceiling. An air return vent sucks air into the ducting that runs across the ceiling joists until it hovers above the area of the furnace. The ducting will then turn and run down the wall framing to the furnace. You may also find exposed areas of ducting in your garage, crawlspace, closets, laundry room, or other spots.

To configure your system, you’ll need to evaluate the route the return air duct will take. Obviously, this is best done during construction but there may be times you have to tear out existing structures to install the return air ducts, such as when completing an addition or finishing a basement space. Since you’re likely adding on to an existing central system, be sure to identify the ducts that come from the furnace and those that return to the furnace. All work you do here will be with the return ducts.

Step 2 - Create Holes for Vents

After you’ve identified the locations for your intake vents, carefully measure the length and width of your chosen vents. Make sure to cut the opening the size of the actual vents, not to the size of the entire vent. In other words, cut the hole smaller than the vent so the outer part of the vent can attach to the wall via the screw mounting holes. Double-check all measurements and then cut through the drywall to the right dimensions. Once the hole is cut, test fit the vent.

Step 3 - Install Ducting

Remove any insulation in the space between studs where you plan to route the ductwork. Then connect the ducting throughout the route to the furnace or to existing ductwork that is already returning air to the furnace. This may be across the ceiling, down the walls, and even into the basement. The ductwork needs to meet local code, so be sure to check before beginning work.

When using duct sheeting, which is a thick, rigid, boxy material meant to be durable, you will need to plan for corners. Preformed corner pieces attach to the straight portions of the ductwork. Measure and cut the straight, rectangular ducting to length up to the point the corner piece will be installed. Then install the corner piece and continue to the next corner in the same manner, connecting straight lengths together as necessary.

Step 4 - Add Return Air Duct to Basement

You can add an air return to the basement (or any other space) by tapping into the ductwork above it. This helps pull cold air out of the basement and provide warm air into the home. Again you’ll need to start by identifying the correct duct to tap into.

Remove any ceiling materials, if applicable. Once you’ve exposed the metal sheathing, mark the spot for your attachment, called a takeoff. Use a circle saw attachment on your cordless drill or simply cut the circle out using metal shears.

The takeoff piece you’ll use is equipped with metal tabs that fold out slightly to attach to the edge of the sheeting. Unfurl about half of the tabs so you can slide the unit into the hole and over the edge. The back tabs will hold it in place while you unfurl the front tabs and fit the other side into the hole. Reach up through the takeoff elbow to tighten the tabs in place. Alternatively, you may find takeoffs equipped with self-stick tape to make the seal. From there, simply attach additional duct pieces to the final destination vent.