Why Use a Through-the-Wall Setup for a Garage?
Most garages lack an existing chimney or flue opening. Running a chimney pipe through the roof means penetrating roof framing, adding flashing, and dealing with potential leaks. A through-the-wall installation avoids all of that. The pipe exits horizontally through the wall via a thimble, connects to a tee, and then runs vertically along the outside of the building.
This approach works well for detached garages, workshops, and outbuildings where you want to heat with a wood stove but keep the installation as simple as possible. It is also easier to inspect and maintain because the entire vertical run is visible and accessible from outside.
What Components Do You Need?
A through-the-wall chimney kit includes everything for a complete installation. Here is what each component does:
| Component | Function | Key Spec |
|---|---|---|
| Wall thimble (wall sleeve) | Creates a fire-safe passage through the wall | Maintains 2" clearance to combustibles |
| Wall support bracket | Carries the weight of the entire vertical chimney run | Must be rated for the pipe diameter |
| Tee with clean-out cap | Connects horizontal wall pass-through to vertical chimney run, allows ash cleanout | Must match pipe diameter |
| Class A insulated chimney pipe | The vertical flue sections that carry exhaust gases up and out | UL 103 HT listed, 2100F rated, 2" clearance |
| Locking bands | Secure each pipe section to the next | One per joint |
| Wall straps/brackets | Secure the vertical pipe run to the exterior wall | Every 4-6 feet of vertical run |
| Rain cap | Prevents rain, snow, and debris from entering the flue | Spark arrestor included |
Stove Pipe vs. Class A Chimney Pipe - Know the Difference
This is a common source of confusion. Stove pipe (also called connector pipe) is only rated for use inside the room, between the stove and the wall or ceiling. It must never pass through a wall, ceiling, or roof. Single-wall stove pipe requires 18 inches of clearance to combustibles, and double-wall stove pipe requires 6 inches.
Class A insulated chimney pipe is the only pipe type rated to pass through walls, ceilings, and roofs. It requires just 2 inches of clearance to combustibles. For a through-the-wall chimney kit installation, Class A pipe is what goes through the wall (inside the thimble) and runs vertically on the outside. The stove pipe stays inside the garage and connects the stove to the thimble.
Step-by-Step Installation
- Check local building codes. Before you buy anything, contact your local building department. Most jurisdictions follow NFPA 211 (Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances), but some states and counties have additional requirements. Some areas require a permit and inspection. Review the building codes overview for more detail.
- Choose your exit location. Pick a spot on the wall where the pipe will exit. Ideally, this is directly behind or near the stove to keep the indoor stove pipe run short. The exit point should be between wall studs. Drill a small pilot hole from inside to outside to confirm your placement.
- Cut the wall opening. Use a reciprocating saw to cut the hole for the wall thimble. The opening must be large enough to maintain the required 2-inch clearance to any combustible framing around the thimble. Measure carefully - the thimble packaging lists the exact rough opening size.
- Install the wall thimble. Slide the thimble sleeve through the wall opening. The thimble creates a rated firestop between the interior and exterior. Secure it according to the manufacturer instructions.
- Mount the wall support bracket and tee. On the exterior side of the wall, attach the wall support bracket. This bracket carries the full weight of the vertical chimney run. Fit the tee into the thimble sleeve. The tee connects the horizontal pass-through to the vertical pipe run, and the clean-out cap at the bottom allows you to remove ash and creosote.
- Build the vertical chimney run. Stack Class A insulated chimney pipe sections above the tee. Lock each section with a locking band. Add wall straps every 4 to 6 feet to secure the pipe to the building.
- Meet the height requirement (3-2-10 rule). The top of the chimney must extend at least 3 feet above the point where it passes through the roof line, and at least 2 feet higher than any part of the building within 10 feet. Even though the pipe runs along the outside wall, this rule still applies. Taller chimneys also produce better draft.
- Install the rain cap. Place the rain cap (with spark arrestor) on the top section. This keeps rain, snow, and debris out of the flue.
- Connect the stove pipe inside. Inside the garage, run stove pipe from the stove collar to the wall thimble. Keep this run as short and straight as possible. Remember: single-wall stove pipe needs 18 inches of clearance to combustibles, double-wall needs 6 inches.
- Inspect and test. Before the first fire, double-check all clearances, locking bands, and support brackets. Light a small test fire to verify proper draft. If your local code requires it, schedule the building inspection before regular use.
Common Challenges and Tips
- Cutting through tough siding. Cement board, brick, or metal siding can be difficult to cut. Use a diamond blade or carbide-tipped hole saw, and always drill a pilot hole first to confirm alignment from both sides.
- Wind exposure. Garages often sit in more exposed locations than the main house. Make sure wall straps are tight and consider adding an extra bracket if your area gets strong winds.
- Draft issues. Exterior chimney runs can be cooler than interior ones, which may reduce draft in very cold weather. A taller chimney run and proper insulation (built into Class A pipe) help maintain consistent draft.
- Garage door clearance. Plan your exit point so the vertical pipe run does not interfere with the garage door track or swing path.
What Size Chimney Pipe Do You Need?
The pipe diameter must match your stove collar outlet. Most small to mid-size wood stoves use a 6-inch flue collar, which means you need 6-inch Class A chimney pipe. Larger stoves (especially those rated for 2,000+ square feet) often use an 8-inch collar, requiring 8-inch Class A pipe. Never reduce the pipe diameter below the stove collar size - this restricts draft and creates a safety hazard.
Related Installations
A through-the-wall garage installation follows the same basic principles as other exterior chimney setups. If you are working on a different building type, these guides may help:
- Installing a Class A chimney in a shed
- Running a chimney flue along an outside wall
- Choosing the best Class A chimney pipes
- External Class A chimney pipe installation
Not Sure Which Kit or Size You Need?
Every garage is different - wall thickness, stove size, roof height, and local codes all affect what you need. Use our free chimney design service to get a custom recommendation within 24 hours. Just tell us your stove model, garage dimensions, and wall type, and we will put together a complete parts list. You can also call us at 888-834-0880 (9 AM - 9 PM, 7 days a week) or browse chimney liner kits and complete chimney kits to see what is available.
Frequently Asked Questions
Do you need a permit to install a chimney in a garage?
In most U.S. jurisdictions, yes. NFPA 211 is the baseline standard, but permit requirements vary by state and county. Contact your local building department before starting. Some areas also require a final inspection before you can use the stove. Check our building codes guide for a state-by-state overview.
What size chimney pipe do you need for a garage wood stove?
The chimney pipe diameter must match the stove collar size. Most small to mid-size garage wood stoves have a 6-inch collar. Larger stoves may use an 8-inch collar. Never reduce the diameter below the collar size, as this restricts draft and violates code.
Can you use single-wall stove pipe through a garage wall?
No. Single-wall and double-wall stove pipe are only rated for use inside the room, between the stove and the wall penetration. Only Class A insulated chimney pipe (UL 103 HT listed) is rated to pass through walls, ceilings, and roofs. Using stove pipe through a wall is a serious fire hazard and a code violation.
How tall does a through-the-wall chimney need to be?
The chimney must meet the 3-2-10 rule: the top must be at least 3 feet above the roof penetration point and at least 2 feet taller than anything within 10 feet. For a single-story garage, this typically means a total vertical run of 10 to 15 feet above the tee. A taller chimney produces better draft.
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