The Wall Thimble is used for through-the-wall chimney installations. It protects a combustible wall as the chimney passes safely through to the outside, and provides a finished look to the framed opening on the inside. Most US exterior walls contain wood framing and are combustible!
The Wall Thimble can adjust to accommodate walls from 6 to 10 inches thick.
Why you should buy our Class A Flues
| Features | Benefits |
|---|
| Made of 304 stainless steel for superior corrosion resistance |
Longer Lifetime - Limited Lifetime Warranty |
| 0.019" thick inner and outer walls (17% thicker than our competition) |
Longer Lifetime - Limited Lifetime Warranty |
| High Density 1.18" thick ceramic fiber blanket insulation ensures no hot spots and no settling of insulation |
Maintains 2" clearance to combustibles over time |
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What is a Wall Thimble?
A wall thimble is a heat-resistant pass-through that allows your stove pipe or chimney pipe to safely cross through an exterior wall. It protects the wall framing and finish materials from the heat of the chimney, while creating a clean and finished look on both sides. Without a wall thimble, you cannot safely run a wood stove chimney through a combustible wall.
Wall thimbles are required by NFPA 211 code for any through-the-wall chimney installation in homes with combustible wall framing (which is most US homes).
Why You Need a Wall Thimble
Hot exhaust gases inside a Class A chimney pipe can reach hundreds of degrees Fahrenheit. Even with insulated double-wall pipe, the outer surface gets warm. Combustible materials (wood framing, drywall, fiberglass insulation) need a buffer of cool air or insulation between them and the chimney. A wall thimble provides exactly that.
- Fire safety: creates the required clearance between hot pipe and combustible wall materials
- Code compliance: meets NFPA 211 clearance requirements for through-the-wall installations
- Clean finish: hides the rough cut around the pipe with a stainless steel collar on both sides
- Insurance: proper installation is often required by homeowner insurance for wood stoves
Wall Thimble Sizing for Your Stove Pipe
Match the wall thimble to your chimney pipe diameter. Most wood stove installations use a 6 inch chimney pipe, which requires a 6 inch wall thimble. Larger fireplaces or open wood fires may use 8 inch.
| Chimney pipe diameter | Wall thimble size |
|---|
| 6 inch |
6 inch wall thimble (this product) |
| 8 inch |
8 inch wall thimble |
Adjustable for Wall Thickness 6 to 10 Inches
Our wall thimble is telescoping, which means it adjusts to fit walls from 6 to 10 inches thick without modification. This covers the vast majority of US wall constructions: 2x4 framing with sheathing and siding (typically 6 to 7 inches), or 2x6 framing with thicker insulation (typically 7 to 9 inches), or older masonry walls (typically 8 to 10 inches).
Simply slide the inner sleeve to match your wall thickness, then secure both flanges to the inside and outside wall surface.
If Your Wall is Only 4 Inches Thick
For walls thinner than 6 inches (such as a thin garage wall or a partition wall), our standard wall thimble may not adjust short enough. Two options:
- Build out the wall: add framing or sheathing to reach 6 inches thickness around the chimney location
- Custom solution: contact us and we can quote a shorter custom wall thimble
Always consult NFPA 211 code or a chimney professional before adapting a thinner wall. Inadequate clearance to combustibles is the leading cause of chimney-related house fires.
Installation Overview
Installing a wall thimble is a straightforward DIY task with the right preparation:
- Mark the chimney pipe path on the inside wall
- Cut a hole large enough for the thimble outer flange (typically 12 to 14 inches square depending on diameter)
- Cut through the exterior wall in the same location
- Slide the wall thimble through from the inside
- Adjust the telescoping inner sleeve to match wall thickness
- Secure both flanges with the supplied screws
- Run your chimney pipe through the thimble
- Seal exterior gaps with high-temperature silicone
For a complete through-the-wall chimney installation including wall thimble, see our Through-the-Wall Wood Stove Pipe Kits. The kits include matching wall thimble plus all other components needed.
Wall Thimble Included in Our Kits
If you are planning a complete chimney installation rather than just replacing a wall thimble, consider one of our complete kits. The wall thimble is included at a discounted bundle price compared to buying components separately.
Why Choose Our Wall Thimbles
- 304 grade stainless steel: superior corrosion resistance for indoor and outdoor exposure
- Adjustable 6 to 10 inch: fits standard US wall constructions without modification
- UL listed: meets U.S. NFPA 211 standards for chimney pass-through
- Limited lifetime warranty: on the thimble itself
- Free design service: we help you size and plan your installation
- Lowest price guarantee: 5 percent refund if you find it cheaper elsewhere
- Fast shipping: typically ships within 1 to 2 working days
For More Information
Want to read more before you order?
Frequently Asked Questions
What size wall thimble do I need?
Match the wall thimble to your chimney pipe diameter. Most wood stoves use 6 inch chimney pipe and need a 6 inch wall thimble. Larger fireplaces or open wood fires use 8 inch.
Is a wall thimble required by code?
Yes. NFPA 211 requires a UL listed wall thimble or equivalent clearance solution for any chimney pipe passing through a combustible wall. Most US homes have combustible wall framing (wood studs).
Can I install a wall thimble in a 4 inch thick wall?
Our standard thimble adjusts from 6 to 10 inches. For thinner walls, either build out the wall to 6 inches around the chimney location, or contact us for a custom shorter thimble.
Do I need a separate wall thimble if I buy a kit?
No. Our Through-the-Wall and External Garage chimney kits already include a matching wall thimble. Buy a separate wall thimble only when you are replacing one or building a custom configuration.
Can I install a wall thimble myself?
Yes. With basic tools (drill, jigsaw, level, screwdriver) and our installation instructions, most homeowners complete the wall thimble installation in a few hours. Always check your local building codes and obtain a permit if required.
How do I seal the wall thimble against rain and air leaks?
Use high-temperature silicone sealant on the exterior flange perimeter where it meets the siding. The interior side typically does not need sealing because the thimble flange covers the rough opening.
Areas of Use
It is for use with free-standing wood stoves, fireplace inserts, fireboxes, fireplaces, furnaces, cook stoves, boilers, and water heaters.
- Additional Info
- Installation
- Deliveries
- Certification
Installation Instructions
If the wall is thinner, the wall thimble can actually be cut down. It’s basically just two sleeves that slide into each other. You can trim one side off if needed. A pair of tin snips is enough to cut it. So you could remove about 2 inches if necessary, and then secure it in place.
If you want to extend it, you’d need some galvanized steel to wrap around it. That’s not something we sell, but most people can get it from a local hardware store. You’d separate the two sections and then fill the gap. You can use something like high-temperature aluminum tape. Some people use rivets.
Click on the buttons below to access installation guides and videos:
Delivery Information
We offer reliable and fast shipping:
- Standard Delivery: From stock, in 3–5 days
- Returns: Within 14 days of delivery
For more details on our shipping policies, click here.
Certification
Certified to meet UL103HT standards, ensuring high safety and performance for residential heating appliances that require a UL103HT chimney system.
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