6″ x 6″ Pivoting Bypass Damper


A “smoke valve” for ensuring easy use of a mass heater, especially cookstoves and heaters with heated benches. The damper is used to provide a direct path to the chimney for priming the chimney and bi-passing a more circuitous heat-retaining pathway. It also ensures that you don’t have smoke spillage during prolonged opening of door for loading of wood or cooking. A convenience worth having!


A bi-pass damper is a smoke valve which allows the user of a masonry or rocket mass heater to switch between a more direct path to the chimney and a longer heat-retaining pathway. They are very convenient for cookstoves, heaters with heated benches, for cold-starts and for ensuring against smoke spillage when opening the firebox door for loading wood or doing any kind of direct cooking inside the firebox.

This style of damper is sometimes called a “butterfly” damper because of the way the shaft turns in place. This is different from a “guillotine” damper where the shaft slides in and out. The butterfly damper offers the advantage that the shaft and handle do not stick out into the living space when in the open position.


  • Frame and paddle are made from 1/4″ steel.
  • Frame has 6″ x 6″ OD. Cross-Sectional Area for flow when open is ~25″ sq. in.
  • Shaft has 1/2″ diameter, standard full length is 24″. Shaft can be cut to length according to project and the handle re-set by grinding a flat indent and tightening set screw on base of handle. Inquire for custom longer shaft.
  • Comes with masonry sleeve and beautifully crafted handle with set screw.

Contact us with any questions. Allow 1-2 weeks between order and shipping.

Weight 160 oz
Dimensions 23.5 × 4 × 4 in
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