How to Attach the Supply and Return to a Gas Furnace

The supply and return connections to a gas furnace consist of ducts that circulate warm or cool air throughout the house and draw air back to the furnace for recirculation. Proper furnace operation requires a secure seal around the ducts at the connection points with the furnace. Duct tape, in spite of its name, is not a good choice for sealing the supply and return ducts to the furnace. The adhesive on duct tape dries with prolonged heat, and the tape material becomes brittle. Over time, duct tape will fall off the duct work so use metallic tape instead.

Screwdriver set
Metallic duct tape
Scissors

Instructions

- 1
  Shut off the furnace to prevent air from blowing while you work.
- 2
  Slide the round duct that returns circulating air to the furnace onto the return port, which is typically the lower of the two ports. Use the tip of a flat head screwdriver to slip the duct around and onto the furnace port. Leave 1 inch of the furnace port exposed as you slide on the duct.
- 3
  Seal the connection with metallic tape wrapped around the furnace port and the duct. The tape must overlap both the furnace port and the edge of the duct for an airtight seal. Three revolutions of tape around the duct are typically sufficient to hold the duct securely in place. Use scissors to cut the tape and press the edge of the tape against the duct to prevent peeling.
- 4
  Connect the supply duct to the upper furnace port in the same manner.

How to Run HVAC Ducts in Floor Cavities

How to Fix a Leaky Heating Element

Heating & Cooling Repair