Flue diameter for your open fireplace

Enter the size of the fireplace opening and set out the chimney route on the drawing. Bends and offsets are counted automatically and you see straight away the minimum diameter the flue needs.

1. Fireplace opening

Width of the opening (cm)

Height of the opening (cm)

Measured inside, at the front of the fireplace.

2. Chimney

Height from the top of the opening to the chimney top (m)

Smoke hood outlet

Horizontal section (m)

3. Offsets

An offset moves the flue sideways with 2 bends of 45°. "At" is the height where it starts, a negative "sideways" goes to the left.

#At (m)Sideways (cm)

Drawing

Drag the blue points: at the top for the height, on an offset to move it or make it wider, at the end of the horizontal section for its length. The pipe is drawn at the chosen diameter.

Result

Minimum diameter, round flue-

Choose at least-

Area of the opening
Air flow
Basic flue cross-section (1/15)
Corrected cross-section

What counts

Item	Number	Factor

Pipe length, approx.

Guide value: the flue cross-section is 1/15 of the fireplace opening, corrected for height, bends and horizontal length. The fireplace manufacturer’s instructions always take precedence.