Backdraught flap - make my own?

Use something like this the blast from the fan opens the flaps to vent when off the flaps shut.

Richard

I should have said it is fitted near the top of the house so an external fitting is non-trivial. That's why I was looking for something to fit in-line.

Something like this

I am sure there are cheaper versions.

This will fail sooner or later (more likely, almost immediately) as aluminium foil is not strong enough.

I love bodges, but this looks like it would be quite difficult to do well. I don't know what your financial position is, but £4.25 does not seem an awful lot for a purpose-made device tht will hopefully last a while.

I have a Vent-Axia in the bathroom which has a backdraft excluder on the rear of the fan. It's 12 years old, but I expect they're still available.

I have another type in another bathroom, which has slats which open on the front when the fan comes on. It uses a thermal solenoid (which are slow, but replaced the earlier versions with a magnetic solenoid which opened with a loud bang). There are two of these exhausting into a common duct, so it stops smells from one room being pushed into the other, although a backdraft excluder in the fans would also work.

Because they won't last very long in an exposed place. That plastic is very prone to crack. I saw a wonderful vent-axia some years ago that had a kind of cam driven Louvre that ran from the fan motor when started and closed when you switched it off. Sorry did not take much notice at the time, but it was on one of those little displays that Children love to play with.

I recall it was not cheap however.. do they still exist or were they just another thing far to complicated to last past the warranty? grin Brian

Very common, but they use thermal (slow acting) solenoids now.