How to Vent a Chimney Through a Wall
If your house lacks a chimney, don’t give up on adding a fireplace. New technology makes it possible to vent fireplaces, stoves and even furnaces through the wall. Gas or propane direct-vent units burn cleanly and create their draw using a cycle that pulls outdoor air into the fire and expels combustion products -- while heating incoming air -- through the same vent. Installation is fairly straightforward, but check with your local building inspector for regulations for a direct-vent unit before installing one.
Locate a spot for your fireplace on an exterior wall away from plumbing pipes or electrical wiring. Although plumbing along an exterior wall is unlikely, there may be electrical wiring.
Assemble the fireplace or stove unit sufficiently according to unit directions so you can determine where the vent pipe will enter the wall. Mark around the vent area by drawing a 10- or 12-inch square -- or a measurement suggested in the directions -- around the circle without touching it.
Drill through the wall from the inside at each corner, using a long, sharp paddle bit. Cut away the wallboard and backing, using the drill holes as guides, until you have a square that opens through to the house wall.
Cut enough lengths of two-by-four lumber to frame the opening so that the holes drilled sit just inside the frame at each corner. Attach the wood framing to the plywood wall with screws.
Saw through the cladding on the exterior of the wall between the holes drilled at the corners of the square to open a square on the outside of the wall. Set a circular saw set low enough to just cut through the siding or clapboards. If your house is brick, you’ll need a masonry blade. Once the wall is open, remove the insulation, house wrap and any other material between the cladding and wall.
Remove the plywood wall using a reciprocating saw. You should now have a 1-foot-square hole through the wall.
Attach the firestop to the framed opening, as directed in the instructions.
Insert the two-piece thimble -- a sleeve -- for the vent, through the wall. Secure the sleeve with silicone or other heat-proof adhesive and insulation as recommended by local building codes and the manufacturer of your unit.
Replace the fireplace or stove and attach the vent. Put the vent through the thimble and attach the gaskets and caps to the exterior, as directed in the kit.
Affix the exterior cap to the vent. You may need to cut away more cladding and insulation to do so. Seal the area between the wall and the cap with heat-proof insulating material.
Things You Will Need
- Vent kit with pipes, gaskets, cap assembly and hardware
- Drill with extra-long bits
- Circular saw
- Utility knife
- Reciprocating saw
- Heat-resistant adhesive
- Heat-resistant insulation
- Galvanized 1-inch or longer wood screws
- 2-by-4 lumber
- Vents can be made directly behind, slightly above or to the side of a corner fireplace. Installations above or to the side of the unit require vents with 90-degree elbows.
- Check your wall with a digital stud finder before cutting so that you cut a hole between studs. Exterior walls are load-bearing; if you cut a stud, you’ll have to open more wall to install headers around your opening.
- Kits differ, but all should have a vent with an inner pipe for hot air out surrounded by a larger one to bring fresh air in. This vent should not be extended -- it will affect the draw. Kits should also include a firestop, sleeve for the wall, gaskets and exterior cap assembly as well as instructions for proper assembly and spacing.
- Always wear eye protection when using saws and other power tools.
- Do not attempt to actually install a gas or electric line or an appliance without assistance from a certified technician or electrician. New installations may also require building permits and inspections.
- Building codes establish minimum distances for combustible materials, such as wood mantels, from fireplace openings. These distances may differ for direct-vent appliances. Check your local building codes.