Wood Stove Clearance & Hearth Pad Calculator: Wall Distance, Shields and Floor Pad Size
Work out wood stove clearances to combustible walls with and without a ventilated heat shield, the hearth pad (floor protector) size from the stove footprint and the front, side and rear extensions (US 16 in, Canada 18 in), the shield size, the floor space the installation takes and the stovepipe clearance.
How it works
Shielded clearance = required × (1 − reduction), rounded up, never below 12″ and never above the unshielded value · reduction (NFPA 211): 24-ga sheet metal, ½″ noncombustible board or 3½″ brick on a 1″ ventilated air space 67%, 3½″ masonry with no air space 33%, tile flat on the wall 0% · hearth pad = (stove width + 2 × side extension) × (stove depth + rear extension + front extension) · floor space = (width + 2 × side clearance) × (depth + rear clearance + front extension) · single-wall connector 18″ (9″ shielded), double-wall per listing
Wood near a stove chars slowly at temperatures well below its ignition point and, after years of drying, can catch fire on a surface that never looked hot (pyrolysis). That is why clearances are generous: 36 inches from an unlisted stove to any combustible (48 inches for an uncertified radiant stove under the Canadian CSA B365 rules), or the tested distances on a listed stove's label and manual, usually 6 to 18 inches. A clearance can be reduced with a heat shield mounted on non-combustible spacers about an inch off the wall, open at the bottom and top so air flows behind it and carries the heat away. Under the NFPA 211 reduction table, 24-gauge sheet metal, ½-inch noncombustible board and 3½-inch brick all cut the side and rear clearance by two-thirds when mounted on a 1-inch ventilated air space; a solid 3½-inch masonry wall built without the air space earns one-third, and tile or thin stone applied flat to the wall earns nothing because it conducts heat into the studs. The calculator applies these percentages, rounds up to the next inch and never goes below 12 inches; if your manual lists its own shielded clearances, choose that option and enter them. The hearth pad, or floor protector, keeps embers and radiant heat off the floor: it extends beyond the stove by the side and rear extension (usually 8 inches) and further in front of the loading door (16 inches in the US, 18 inches in Canada). The shield itself should run 18 inches past each side of the stove and 20 inches above it.
Worked example
A listed stove 26″ wide and 22″ deep whose manual asks for 12″ at the rear and 16″ at the sides, with no shield, stays 12″ from the back wall and 16″ from side walls. Its hearth pad must be at least 26 + 2 × 8 = 42″ wide and 22 + 8 + 16 = 46″ deep, 13.4 sq ft. The installation occupies (26 + 2 × 16) × (22 + 12 + 16) = 58 × 50″ of floor. With a ventilated sheet-metal shield the sides would drop to 16 × 0.33 = 5.3″, which is raised to the 12″ minimum, and the rear stays at 12″. Single-wall connector pipe needs 18″ to combustibles.
Sources: Wood Heat Organization: installation clearances, floor protection and shields · Wood Heat Organization: installation rules for flue (stove) pipes · Wood Heat Organization: wood heat safety · Maine Fire Marshal, standards for solid-fuel stoves (NFPA 211 reduction table, 12″ wall minimum) · City of Lincoln (NE), wood stove installation chart
Frequently asked questions
How far does a wood stove need to be from the wall?
An unlisted stove needs 36 inches from any combustible surface. A listed (certified) stove needs the distances on its label and in its manual, typically 6 to 18 inches at the rear and 12 to 24 at the sides, and less in a corner installation.
Can I use a heat shield to get below 12 inches?
Not with the NFPA 211 percentages: 12 inches is the floor after any reduction. Some listed stoves with built-in rear heat shields are tested to less; only the manual can allow that.
How big should a hearth pad be?
The stove footprint plus the side and rear extension, usually 8 inches on each side and behind, plus 16 inches in front of the loading door in the US or 18 inches in Canada. The manual also states whether the pad needs an insulating (R-value) rating or only ember protection.
Does tile on drywall count as a heat shield?
No. Tile, brick or stone applied directly to drywall or wood earns no clearance reduction because heat conducts through it into the framing. A shield needs about a 1-inch air space behind it, open at the bottom and top.
How far does stovepipe need to be from the ceiling and walls?
Single-wall connector pipe needs 18 inches to combustibles, which shielding can cut by half to 9 inches. Listed double-wall connector pipe needs only what its label says, often 6 inches.
What counts as combustible?
Drywall over wood studs is combustible because the studs are, and so are wood floors under tile without proper floor protection. Only masonry walls with no wood framing behind them are non-combustible.
Related calculators
Typical values from NFPA 211, CSA B365 and the Wood Heat Organization. The stove's label and installation manual, the local code and a certified installer or chimney sweep govern clearances, floor protection and venting. Install smoke and carbon monoxide alarms.