DIY: Venting Options for Gas Fireplace Inserts

Direct Vent Installation

• 1

  Mark the spot where your direct-vent fireplace’s vent will pierce the wall. Cut a 12-inch square opening through the drywall between the studs. Measure the vertical distance to the hole from the floor and the horizontal distance from the nearest room corner. Record those measurements. Cut out the surrounding drywall panel with a drywall saw and remove it to expose the studs around the hole. Remove any insulation.

• 2

  Locate the bottom of the 12-by-12-inch opening by measuring up from the floor. Set a level 2-by-4 horizontally between the wall studs at the measured mark and toenail the ends to the studs on each side. Frame the top of the hole by installing another level horizontal 2-by-4 member 12 inches above the bottom framing member and toenailing it to the wall studs. Cut two 12-inch-long 2-by-4 pieces to fit between the horizontal members. Locate the first side framing member by measuring from the nearest room corner. Set the member plumb at that mark and drive two nails into it from above and two from below to secure it. Install the other side framing member 12 inches from the first. Set it plumb and nail from above and below to secure it.

• 3

  Drill through the wall at each corner of the 12-by-12 framed opening to mark the hole’s location from the outside. Cut through the exterior siding and sheathing with a circular saw. Trim the corners with a wood chisel. Mark around the outside of the opening to the size of the fireplace vent’s exterior firestop and cut away only the siding. Leave the sheathing in place.

• 4

  Replace the insulation and interior drywall panel. Seal the edges of the panel and the vent hole with caulk. Place the interior sheet metal firestop in the opening. Secure the edges with screws spaced 2 inches apart. Slide a section of the coaxial fireplace vent pipe through the interior firestop, working from the outside. Attach the coaxial vent pipe to the fireplace’s vent opening as directed by the manufacturer. Seal the joint between the pipe and the interior firestop with high-temperature silicone caulk.

• 5

  Slide the outside firestop and vent termination assembly over the end of the coaxial vent pipe. Secure the firestop and termination assembly to the sheathing with screws 2 inches apart. Caulk around the edges. Slide a sheet metal drip cap under the siding at the top of the vent. Finish the fireplace by hooking up gas and electric connections and installing the mantel and decorative surround.

Natural B-Vent Installation

• 6

  Plan your fireplace location and vent route to avoid cutting rafters or joists, or moving plumbing or wiring. Mark the ceiling directly above your fireplace vent outlet. Cut a hole through the ceiling with the reciprocating saw, making it 2 inches larger than the diameter of the vent pipe.

• 7

  Install the vent pipe support assembly in the ceiling according to manufacturer’s directions. Nail it to the ceiling joists. Connect the bottom of the vent pipe to your fireplace vent opening as directed by the manufacturer. Pass the vent pipe through the support assembly, clamp the pipe in place and secure it with 3/8-inch sheet metal screws. Slide a sheet metal firestop over the vent pipe and nail it to the floor.

• 8

  Install additional lengths of vent pipe, fastening each new section with a clockwise twist and securing it with sheet metal screws. If the pipe passes through habitable space in an upper story, enclose it with a frame assembled from 2-by-4 lumber and covered with fire-resistant drywall. Pass the pipe up through the attic floor. Install another sheet metal firestop and nail it to the attic floor.

• 9

  Cut a hole through the roof that's 2 inches larger than the vent pipe diameter, using the reciprocating saw. Pass the vent pipe through the hole. Slide the roof flashing assembly over the pipe from the outside until its base sits on the roof. Slide the upper-side flange of the flashing under the roof shingles. Rest the lower-side flange on top of the shingles. Nail the flashing to the roof. Coat the edges with roof cement. Slide a drip collar down over the top of the flashing and seal it with high-temperature sealer.

• 10

  Add pipe segments above the roof line until the pipe is 3 feet above the roof line or 2 feet higher than any part of the roof within 10 feet of the vent pipe. Slide a rain cap over the end of the vent pipe and secure it with wood screws. Finish your fireplace by hooking up gas and electric lines, and installing the mantel and decorative surround.