Flue Liner Size Calculator: What Size Do You Need for a Wood Burner?

Reline a chimney with the wrong diameter and you either choke the stove or lose your draught, and Building Regulations set a floor on both size and height. This calculator turns your stove and chimney into a recommended liner diameter and the length of flexible liner to order. The catch most people miss: a flue liner can never be narrower than the stove's own outlet, so the 5 inch spigot on the back of your stove does not automatically mean a 5 inch flue is allowed.

These figures follow the general rules in Approved Document J for solid fuel appliances: a flue liner is never smaller than the appliance outlet, at least 150mm for solid mineral fuel, and at least 4.5m tall for a decent draught. A dedicated wood burner may drop to 125mm only where the manufacturer has approved it and the flue is close to straight. Relining is notifiable work, so use a HETAS registered installer or notify Building Control, and always check the figures against your own stove's instructions.