Clearance to Combustibles Reference
Pick the hot surface and read the typical air gap code wants between it and anything that can burn. Single-wall stovepipe is the big one — 18 inches.
1 Enter your numbers
Clearance-to-combustibles is the air gap code requires between hot chimney/appliance surfaces and anything that can burn. For Masonry chimney to interior framing the typical is about 2" — but the exact number is set by the appliance / chimney LISTING and local code. These are LABELED typicals, never a substitute for the manufacturer’s instructions.
Clearance to combustibles is the required air gap between a hot chimney or appliance surface and anything that can burn — framing, sheathing, trim, insulation, a mantel. It is one of the most common code failures a sweep finds, and it is the difference between decades of safe use and a slow-cook fire inside a wall. The numbers below are typical published values so you know what "right" roughly looks like — but the binding figure is always set by the appliance and chimney listing and by local code, never by a rule of thumb.
The single biggest gap most people underestimate is the connector pipe — the stovepipe between a stove and the chimney. Plain single-wall pipe wants a full 18 inches to a combustible wall or ceiling, because it radiates a lot of heat. Switch to listed double-wall pipe and that typically drops to about 6 inches. Masonry chimneys are tighter: roughly 2 inches to interior framing and about 1 inch where the chimney runs up an exterior wall. A listed factory-built chimney carries its own tested clearance, often around 2 inches.
Where you truly cannot make the gap, code-approved shielding or a listed reduced-clearance product — not just "moving it a bit closer" — is the only legitimate way to cut the distance.
Why the connector figure is so much larger than the masonry one throws people, so it is worth saying plainly: a masonry chimney has mass and often an air space that carry heat away, while a bare single-wall stovepipe radiates directly at whatever faces it. That is the whole reason double-wall pipe exists — the air gap between its two walls does the same job as distance, which is how it earns a much smaller required clearance.
Formula
There is no formula — clearance is looked up by surface, and the appliance/chimney listing governs:
Masonry interior ≈ 2" · Masonry exterior ≈ 1" · Factory chimney ≈ 2" · Single-wall connector = 18" · Double-wall connector ≈ 6"
Listed heat shields can reduce a required clearance by a rated amount — follow the shield’s instructions exactly.
Worked example
You are setting a wood stove in a corner and the connector pipe runs about 14 inches from a stud wall. With plain single-wall pipe that is a violation — the listing wants 18 inches. Two legitimate fixes: swap to listed double-wall connector, which typically needs only 6 inches, or add a code-approved wall shield with a ventilated air gap that reduces the single-wall requirement. What you cannot do is leave bare single-wall pipe at 14 inches and call it close enough — that hidden radiant heat is precisely how a wall behind a stove chars and, eventually, ignites.
What counts as combustible (and common mistakes)
Measure before you order: the clear distance from the outside of the hot surface to the nearest combustible, at the tightest point — usually where pipe passes a wall or ceiling. Trim, a wood mantel and blown-in insulation all count as combustible.
Common mistakes: treating single-wall and double-wall pipe as interchangeable, forgetting that a mantel over a firebox has its own clearance, and reducing a gap with drywall or cement board laid flat against the wall (a proper shield needs a ventilated air space). Model code and listings come through your local building department and standards bodies such as NFPA and ICC; when in doubt, defer to the appliance manual and a licensed installer.
Reference table
| Hot surface | Typical clearance |
|---|---|
| Masonry chimney to interior framing | 2" |
| Masonry chimney, exterior | 1" |
| Factory-built (listed) chimney | 2" |
| Single-wall stovepipe connector | 18" |
| Double-wall connector | 6" |
Typical values only — the appliance and chimney listing and local code set the real number, and shielding can reduce a connector clearance.
Frequently asked questions
How close can a stovepipe be to a wall?
Plain single-wall connector pipe typically needs 18 inches to a combustible wall or ceiling. Listed double-wall pipe usually needs about 6 inches. A code-approved ventilated shield can reduce the single-wall figure — always follow the product listing.
Can I reduce clearance with a heat shield?
Yes, but only with a listed or code-approved shield installed with a ventilated air gap behind it, and only by the amount its instructions allow. Board laid flat against the wall does not count — the air space is what does the work.
What clearance does a masonry chimney need?
Typically about 2 inches to interior framing and roughly 1 inch where the chimney runs along an exterior wall, with the gap kept free of debris. The exact requirement comes from local code, so confirm before you frame or insulate around it.
What if I cannot meet the clearance?
Use a listed reduced-clearance product (double-wall pipe, a listed shield) or relocate the appliance or run. Never simply move a hot surface closer than its listing allows — that concealed heat is a genuine fire cause. A licensed installer can spec a compliant option.
Does the mantel over a fireplace have a clearance too?
Yes. A combustible mantel or trim above a fireplace opening has its own clearance in the appliance or fireplace listing, usually expressed as a minimum height above the opening that increases the further the mantel projects. A deep, low mantel is a frequent violation, so check the listing before you build or reface, and treat a wood mantel as combustible even if it looks massive.