What is the purpose of a back valve in ventilation and when do you need it?

The back valve is a ventilation component mounted on the fan collar or further along the ventilation system, preventing the flow of reverse air currents and unwanted odors after the fan is turned off.

Types of check valves:

Considering the installation location, we can distinguish:

  • valves mounted directly at the end of fan bodies and ventilation grilles.
  • valves mounted on ventilation system components, in ventilation ducts.

Taking into account the material from which the back valve is made, we can distinguish:

  • all-plastic valves.
  • metal/aluminum valves.
  • foil valves, where the frame is made of plastic and the flap itself is made of rigid, transparent plastic foil.

Plastic valves are used directly in ventilation ducts and grilles. Some manufacturers also use such valves in fans.

Metal and aluminum valves are used in ventilation ducts. 

Foil valves are used exclusively at the end of fans.

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When do you need a back valve?

In ventilation, check valves must be used in situations where:

  • air is expelled directly through the wall of the house.
  • when air is discharged into a common ventilation shaft.
  • when air is discharged into a chimney.

When definitely do you not need to install a back valve?


When you use the recirculation mode, which means that air is not extracted from the room but only filtered and returned to it (often the case with kitchen hoods without the function of venting air to a duct or chimney).

Rectangular connector with wall flange and back valve

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