How to Connect a Double-Wall Pipe to a Water Heater

Vent piping removes gases from the combustion chamber of a water heater. The heat generated by water heater exhaust can ignite combustible materials surrounding the heater vent, so gas water heaters have double-wall exhaust pipes. Double-wall vent pipe consists of an inner wall that removes exhaust gases and an external wall that keeps heat contained and away from materials surrounding the heater. It's a pipe within a pipe, essentially. When properly connected to a water heater, double-wall pipe will safely exhaust fumes while reducing the amount of room needed between the outside wall of the vent pipe and combustible materials.

Vent piping exhausts harmful fumes from gas water heaters.

Step 1

Pull a tape measure across the opening of the inner wall of a doubl-wall pipe. Measure the vent opening on top of the water heater.

Step 2

Purchase a draft hood with one side matching the interior size of the double-wall pipe and the other side matching the size of the water heater vent opening.

Step 3

Slide the draft hood opening -- matching the size of the vent opening -- on the opening of the water heater. Run four evenly spaced self-tapping screws through the draft hood and into the collar surrounding the heater vent, using a screw gun.

Step 4

Align the interior opening of the double-wall pipe with the open side of the draft hood. Push the pipe on the hood opening. Ensure the front edge of the pipe sits against the ridge located near the taper of the draft hood.

Step 5

Secure the double-wall pipe to the draft hood with four evenly spaced self-tapping screws.


  • Overtightening self-tapping screws will cause them to strip, allowing the connections to move. This allows gas to escape from the connections.
Continue Reading