Revolving chimney cowls are designed to cure the problems caused by downdraught. The cowl spins, either when the wind blows, or when your appliance is burning well, when the heat on the underside of the cowl will make it spin.

When spinning, they will slightly increase the draw within your chimney stack, although they are not a magic solution for lack of updraught. 

Revolving Anti-Downdraught Chimney Cowls

MAD Spinner Revolving Chimney Cowl
The MAD Spinner cowl is a British made revolving chimney cowl designed to eradicate downdraught, whilst the rotating action assists ventilation. Stainless steel construction. Available in brown, black or raw stainless steel.

Rotorvent Revolving Chimney Cowl
Wind driven revolving chimney cowl. Stainless steel construction. Now available in two sizes. Can be used on chimneys with appliances fired by gas, oil or solid fuel. 

Midtec Roto Cowl - BS715
The BS715 Roto Cowl is a revolving anti-downdraught chimney cowl, designed to cure downdraught in chimneys. The Roto Cowl can be used on chimneys with appliances fired by gas, oil or solid fuel. 

Aspiromatic Revolving Chimney Cowl
Wind driven revolving chimney cowl. Stainless Steel Construction. 3 sizes cover diameters from 80mm (3") to 240mm (9.5"). Also available with a square base for use where there is no chimney pot.