How to Install a Gas Water Heater Vent Through the Roof


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Hot water is an amenity that most people just can't live without. When installing a gas water heater, building codes requires that they be ventilated out of the room, through the attic, and out through the roof. In order to do this, two critical measurements must be taken: one on the ceiling above the water heater and one that is the distance from the attic floor to the roof. Once these measurements are recorded, you are ready to begin. Be certain there is nothing in the attic to prevent cutting a hole for the vent. You will also need to check the requirements of the water heater to determine the size of the vent pipe needed.

Items you will need

  • Water heater vent pipe (double walled)

  • Roof vent boot

  • Screw driver

  • Jigsaw

  • Drill

  • Plumb bob

Mark the ceiling above the water heater to receive the pipe. Use the plumb bob to be certain the center of the pipe at the ceiling and the center or the boot on the water heater are lined up.

Cut the hole with the jigsaw. In the attic, use the plumb bob to mark the center of the hole to be cut for the roof vent boot.

Drill a starter hole with the drill. Insert the blade of the jigsaw through the hole and cut the hole. Be careful not to oversize the hole, as this will cause a potential leak in the roof.

Install the pipe, securing each joint as needed. On the roof, slip the roof vent boot over the protruding pipe to be certain of the fit.


Install the roof vent boot so that water will flow over it where it meets the roof. This will require slipping the flange under the roofing shingles.


  • Do not reduce the size of the pipe, as this can cause inadequate ventilation, resulting in carbon dioxide poisoning.


  • Always wear safety glasses.
  • Keep a tube of roofing caulk handy in case the area around the roof vent boot needs to be resealed.