Keep a stove clear of combustible walls, fit a spark arrestor and a non-combustible hearth, keep 5 cm of non-combustible material between a chimney and any wood, and clean the chimney at least once a year. The fire guide’s 40 cm wall clearance is thin for a bare stove: an assumed 0.5 m by 0.8 m stove face at 400 C puts about 4.9 kW/m² on a wall 40 cm away, enough to hold a blackened wall near 220 C, against 1.5 kW/m² and about 103 C at 90 cm, so add a spaced metal shield or the larger distance.
Part of Fire Prevention in Settlements
Chimney and stove safety is the set of clearances, hearth, arrestor and cleaning rules that stop the most common starting point of a building fire, the stove and its flue.
Most Building Fires Start At The Stove Or The Chimney
The fire guide says so and sets five rules. A chimney passes through the roof with at least 5 cm of non-combustible material (stone, brick, clay) between it and any wood framing. A mesh spark arrestor of salvaged hardware cloth caps the top, essential in dry or windy conditions. The hearth is a non-combustible floor extending at least 40 cm in front of the stove opening and 20 cm to each side. A wood stove stands at least 40 cm from combustible walls, or behind a metal heat shield with a 2 cm air gap. And the chimney is cleaned at least once a year, more with resinous wood, because creosote is the most common cause of chimney fires.
Four of these are sound as stated. The wall clearance is the one to test, because radiant heat falls steeply with distance.
Worked Example: A Bare Stove Against A Wall
Inputs, all assumed for the example, since no stove temperature is given in the corpus: stove face 0.5 m wide and 0.8 m tall, surface at 400 C (673 K), emissivity 1; the wall facing the centre of the stove, blackened, losing heat only by convection (10 W/m²K, an order-of-magnitude figure) and re-radiation, with none conducted into the wall.
- Emitted flux: σT⁴ = 5.67 × 10⁻⁸ × 673⁴ = 11,600 W/m², 11.6 kW/m².
- View factor to the wall, from the rectangle formula in the spacing article (Fire Breaks & Building Spacing), with X = 0.5 ÷ (2d) and Y = 0.8 ÷ (2d): at d = 0.40 m, F = 0.42; at d = 0.60 m, F = 0.25; at d = 0.90 m, F = 0.13.
- Flux on the wall: 0.42 × 11.6 = 4.9 kW/m² at 40 cm; 0.25 × 11.6 = 2.9 kW/m² at 60 cm; 0.13 × 11.6 = 1.5 kW/m² at 90 cm.
- Wall temperature where heat gained equals heat lost: about 220 C at 40 cm, 159 C at 60 cm and 103 C at 90 cm.
A wall held for hours near 220 C is far above room temperature. Wood kept hot for a long time well below its ignition temperature slowly chars and becomes easier to ignite; this is a general property of wood that I am recalling, not a figure from this corpus. The 40 cm figure therefore leaves a small margin for a bare, hot stove. As I recall, US practice asks about 90 cm (36 inches) from combustible walls for an uncertified bare stove, and about half that with a ventilated metal shield, but I have not checked that against a local code. Use the shield, or the larger distance, and a hotter stove needs more.
What You Need
- Stone, brick or clay around a chimney where it passes wood: at least 5 cm
- A mesh spark arrestor of hardware cloth, cleaned and replaced when blocked
- A non-combustible hearth: 40 cm in front and 20 cm each side or more
- A metal heat shield with a 2 cm air gap behind it where the stove is near a wall
- A weighted brush or chain, or a proper chimney brush, and a ladder
Method: Install And Maintain
Step 1: Set the stove on the hearth, as far from combustible walls as the room allows, and shield the wall.
Step 2: Build the flue straight and of stone, brick or clay, with the 5 cm of non-combustible material where it passes wood or thatch (Chimney Draft gives the flue sizing).
Step 3: Fit the arrestor at the top, and look at it each cleaning.
Step 4: Burn dry fuel, hot and clean. Wet or resinous fuel makes creosote.
Step 5: Clean the flue at least once a year, on the schedule in Chimney Cleaning Schedule.
Step 6: Keep fuel, rags and bedding well back from the stove and out of the hearth zone.
Common Mistakes
- Treating 40 cm as safe for any stove. Hotter and larger stoves need more.
- A flue through the wall with no gap in straw bale or timber (Plaster as a Fire Barrier).
- A blocked arrestor. It chokes the draft and sends smoke and carbon monoxide into the room.
- Drying clothes on or over the stove.
Safety
Chimney fires and carbon monoxide
A chimney fire roars and throws sparks from the top. Shut the air supply, get everyone out, wet the neighbouring roofs and do not pour water into a hot flue. A stove with a weak or blocked draft also puts carbon monoxide into the room; never sleep with a stove burning in a closed room (Carbon Monoxide Risks).
What’s Next
- Learn next: Chimney Cleaning Schedule — how often, and how
- Combine with: Ember Protection — the arrestor’s other job