How the Back Draft Shutter Works
The Back Draft Shutter is a cylindrical insert that can be fitted into the ducting of your extraction system to stop air from escaping from the grow area when the duct fan is turned off. Inside the cylindrical insert is a centrally mounted support which accommodates two sprung shutters which resemble butterfly wings. When air movement is created by your duct fan, the shutters open up to allow airflow to continue on to the outlet point. As soon as the duct fan is turned off, the lack of air movement triggers the shutters to close up. It should be noted that the shutters may have a very slight impact on the number of cubic metres of air moved per hour by your duct fan, though the effects will be fairly negligible.
We recommend that your extraction system is run continually. For instance, in situations where temperatures are dropping too low, duct fans should not be turned off, but should instead be regulated to lower their output with a fan speed controller. However, it's advisable to plan for potential worst case scenarios, and it is always possible that your extraction system may at some point be inactive for a period of time. This could be for maintenance reasons or it could be due to a power cut or other failure.
As your extraction system is usually responsible for removing odours from the air via a carbon filter, an inactive duct fan can lead to smells escaping from your indoor garden. In the event that this happens, having a back draft shutter fitted into your ducting helps to stop unwanted odours from finding their way outside, with the shutters acting as a barrier between the grow area and the exterior.