What is the maximum allowed bend or offset in a domestic flue?

Offsets should generally not exceed an angle of 30 degrees to the vertical to maintain proper draft.

How high should a domestic chimney be above a pitched roof?

It should extend at least 600 mm above the ridge line to prevent downdrafts caused by wind turbulence.

What is the minimum clearance required from combustible timber?

A minimum clearance of 150 mm is generally required between the inside of the flue and any combustible building material for fire safety.

IS 1649

: 1962

Code of practice for design and construction of flues and chimneys for domestic heating appliances

CurrentSpecializedCode of PracticeBIMMEP · Building Construction Practices incl. Painting, Varnishing

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This code covers the design, construction, and fire safety clearances for flues and chimneys used with domestic heating appliances to ensure efficient smoke draft and structural safety.

Code of practice for design and construction of flues and chimneys for domestic heating appliances

Quick Reference Values

max angle of offset30 degrees from vertical

min clearance from combustibles150 mm

min height above roof ridge600 mm

Practical Notes

Keep flue paths as straight as possible to minimize draft resistance and soot accumulation.

Ensure structural timber and other combustible materials strictly maintain the minimum clearance from the chimney to prevent fire hazards.

Chimneys should terminate well above the highest point of the roof (ridge) to avoid wind-induced downdrafts.