Cold air from range hood ventilation

[Eldad]

As part of our rear extension project, out builder had installed ducting for a range hood.

We feel cold air coming out of the range hood whenever it is not working. 

The are non return valve installed on the hood but it seems strange to me that cold air should be getting all the way up to the hood instead of being blocked outside the property. 

We have a backdraft dumper (see photos and I hope I'm using the right terms) installed but I'm not sure if it's doing its job. 

 

Is this normal? Should the cold air only be blocked by the range hood itself and not before?

[MJNewton]

Are you sure that terminal has something in it to prevent backdraft? To me it look like the type fitted to many a log burner, and just serves to let smoke out and prevent rainwater getting in.

[markocosic]

Cold air will enter the vent and hot air will rise out of the roof with the stack effect.

 

The back draught flaps are for howling takes only; not to prevent all airflow.

 

Fix with recirculation and carbon filters and/or better airtightness in the rest of the house.