Flue through a wall

When a flue through a wall is suitable

• A new wood stove, boiler or sauna stove in a room that has no chimney.
• An extension, garage or sauna where taking a chimney through the roof is complicated.
• A house with finished rooms, where a chimney through the storeys would mean major building work.

For a solid fuel appliance a flue through a wall does not end at an outlet in the wall. It has to go up to the roof, because the height requirements apply to every flue. A gas condensing boiler has other options, including a concentric flue with an outlet on the facade: gas boiler flue.

The wall passage: the most important point

The wall is where the hot flue is closest to the structure of the house. In a masonry or concrete wall the passage is simpler: an insulated section or a passage element is set in the opening and the gap is filled with non-combustible insulation. In a timber, timber-frame or log wall a larger opening is needed, with a non-combustible passage box and insulation through the whole wall thickness, so the timber does not overheat even after hours of firing.

The horizontal section is short and rises slightly towards the outside. A long horizontal section reduces the draught and collects soot. Outside, the section ends in a T-piece: the chimney goes up, and the cleaning door and condensate collector go down.

How installation is done

1. Position on the facade We choose a position where the chimney does not cover windows, is not next to a balcony or terrace and can rise above the roof at the right distance from the ridge.
2. Opening and passage We make the opening in the wall and fit the passage element with insulation and the horizontal section.
3. Bracket and T-piece We fix a support bracket to the facade and mount on it the T-piece with the cleaning door and condensate collector.
4. Chimney up the facade We stack the sections upwards and fix them to the wall with brackets at the distances the manufacturer specifies. Around the eaves we route the chimney with bends or offset it from the wall.
5. Above the roof We take the top section up to the height set in the building codes, brace it with guy wires if needed and fit a cap.
6. Connection and certificate We connect the appliance and check the draught.

How high a facade chimney must be

This is exactly where facade flues most often fall short: they end at the eaves or just above them, and the wind pushes smoke back onto the wall or the windows. The top of the chimney must be at least 0.5 m above the roof covering. If it is closer than 1.5 m to the ridge, it must be 0.5 m above the ridge; if 1.5–3 m from the ridge, no lower than the ridge; if further, no lower than a line drawn from the ridge at 10° to the horizontal. That is why a chimney on a gable wall far from the ridge turns out longer than expected. More detail: chimney height above the roof.

Certificate and safety

If an appliance is replaced with another, before the new appliance is used the regulations require a technical condition inspection certificate stating whether it may be connected to the flue. Photos or video are attached to the certificate.

How much does a flue through a wall cost?

There is no single price. It depends on the wall material and thickness, the chimney length up to the required height above the roof, bends around the eaves, the number of fixings, access (ladders, scaffolding or a lift) and the flue diameter. Materials are priced separately. Describe in the form where the flue could run, and the specialist will name the price before the work. Other prices: prices.