Flueet — Chimney flue sizing, draught and liner choice | flueet.com
Most wood burners between 5 and 12 kW take a 125 mm or 150 mm flue; the stove's outlet and its kilowatt output decide which.
Start at the back of the stove. Every appliance leaves the factory with a flue outlet of fixed diameter, and the rule for a sealed stove is that the chimney must be no smaller than that outlet — roughly 100-130% of its cross-sectional area. If the outlet is 150 mm, no part of the flue run may be 125 mm, whatever an adapter claims.
With the outlet satisfied, output in kilowatts picks the standard diameter. An insulated twinwall flue of 125 mm internal diameter covers appliances of about 5-8 kW; 150 mm covers about 8-12 kW. Most domestic wood burners sit inside those two bands, which is why 125 and 150 mm dominate the shelf.
On narrow screens, swipe or scroll the plate sideways.
Open fires play by a different rule because there is no outlet to match. Instead, the flue cross-section should be 12-20% of the fireplace opening area, with 15% the usual target — which in practice means liners of 175-200 mm.
The construction of the run changes the space you need around it, not the diameter itself. Single-wall stove pipe must sit three times its diameter from combustibles — 375 mm for a 125 mm pipe — while insulated twinwall is usually stated at 50-65 mm by manufacturers.
Once the diameter is chosen, two checks remain. Measure the draught at the outlet to prove the size on paper, and confirm the liner carries the right EN 1856-1 rating for wood service; both checks have their own guides on this site.
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