A kwibus is a revolving cowl on a chimney, related to the Dutch “gek”, the revolving chimney cap, but with a larger opening. Because that opening is larger, the cowl makes a smaller angle with the horizon: the kwibus sits flatter.
Like the revolving cap, the kwibus turns with the wind. A vane keeps the opening facing away from the wind. Wind passing over the cowl creates a negative pressure there, and that suction strengthens the draught of the flue.
Why a revolving cowl
A chimney may draw badly for two reasons:
- Too little buoyancy — the flue is too cold, too short or too wide
- Downdraught — wind passing over a higher roof, a tree or a neighbouring building presses into the chimney and pushes smoke back into the room
A revolving cowl such as the gek or the kwibus helps mainly with the second problem. The opening always sits in the lee, so the wind can no longer press into the flue.
Use and points to watch
The kwibus belongs to the classic family of chimney cowls and is still found on older buildings and with open fires. It is barely used in new build, where appliance connections are standardised and fixed draught-improving terminals are used instead.
With a revolving cowl, note that:
- It has to keep turning — the bearing silts up and corrodes; a seized cowl can actually make the draught worse if it stops in the wrong position
- It must suit the appliance — for room-sealed appliances and boilers with a concentric or balanced flue a revolving cowl is not permitted. Always follow the manufacturer’s installation instructions
- The chimney height must be right — a cowl is no substitute for sufficient height above the ridge and surrounding obstructions
- Maintenance must be feasible — a moving part on a chimney needs periodic inspection alongside the regular sweeping
Related terms
- Chimney
- Chimney cowl
- Flue
- Draught
- Open fire
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