Flue Sizing
To clear the smoke and fumes from a fireplace or appliance the flue must be correctly sized. If it is too small an insufficient volume of air will pass through it – resulting in a smoky fire. Too large a flue will cause cooling of the flue gasses, slowing down the flow with similar results.
All the above should be increased by 25mm if there is a bend in the flue.
| Type of Fire | Flue Size | Taken from: |
|---|---|---|
| 400 / 450 mm open fire | 225 mm (min. 200 mm) | Building Regulations 2002 |
| Larger open fire | 15% of opening size (WxH) | and BS 6461 1984 |
| Closed appliance | 150 mm |
The above table gives recommended flue sizes for most types of fireplace and appliances. For chimneys less than 5 metres high use one size larger than quoted. Always refer to manufacturers installation instructions for their recommendations.