How to Install a Duct Vent Fresh Air Intake for a Furnace

With today's homes being built increasingly airtight, it is becoming essential to bring fresh air into the home mechanically. Without fresh air, the home becomes stuffy and deadly combustion gases may build up. Also, with the increasing concern of radon infiltration, fresh air becomes an even greater need. Fresh air is brought in from an outside intake hood and dispensed in the return air duct. It is then heated by the furnace and distributed through the home. It is easy to install a fresh air intake for a furnace.

Things You'll Need

  • 6-inch fresh air intake hood

  • 6 1/4-inch hole saw

  • Drill

  • 1 1/2-inch exterior wood screws

  • Exterior caulk

  • Caulk gun

  • 6-inch galvanized ducting

  • 6-inch galvanized duct fittings

  • 6-inch galvanized pipe collar

  • Sheet metal screws

  • Tape measure

  • Aviation snips

  • Pipe crimper

  • 6-inch barometric damper

  • Adjustable wrench

  • 1-inch galvanized hanger strap

  • Silicone caulk

  • 1 1/2-inch foil faced duct wrap

  • 2-inch aluminum foil tape

Step 1

Locate a spot for the fresh air intake hood on the outside of the home. Keep the intake hood away from exhaust vents, dryer vents, and furnace vents. You don't want to bring any of those exhaust gases back into the home heating system.

Step 2

Drill a 6 1/4-inch hole with your hole saw. Slide the 6-inch pipe stub on the hood through the hole and fasten the intake hood to the home with screws. Caulk around the hood with a high-quality exterior caulk.

Step 3

Cut a 6-inch diameter hole in the return air duct with your aviation snips. Generally try to keep this close to the furnace if possible. Install a 6-inch metal sheet metal collar into the hole.

Step 4

Install your 6-inch metal galvanized duct from the collar to the stub that comes in from the intake hood. Screw all joints together with sheet metal screws. For cut joints, crimp one end with your pipe crimper to fit it into the next piece. Right before you connect to the intake hood stub, install a 6-inch barometric damper. This will keep the outside air from coming into the duct until the furnace turns on. Ensure the arrows on the barometric damper are facing toward the furnace. These arrows signify which way the airflow will go, and you want air to flow from outside toward the furnace.

Step 5

Support your galvanized duct with 1-inch galvanized hanger strap. The best way to hang the duct is to screw one end of the strap into a support member, then wrap the strap around the duct and screw the other end into a support member. The strap will look like the letter U, with the galvanized duct sitting in the crotch of the U.

Step 6

Caulk all seams and joints of the duct so that it is airtight. Insulate the duct with a high-quality 1 1/2-inch foil-backed duct wrap. This will ensure the duct doesn't sweat during the colder winter months.


Once installed, adjust the weights of the barometric damper to control how much fresh air gets to the furnace. If you live in a cold climate, you may not want the damper to open too much in the winter.


Failure to properly caulk the seams and joints of the fresh air intake duct could allow dangerous combustion gases to leak into the home heating system.