100mm Backdraft flaps for Bathroom extractor fan

[mark.carline]

I will soon be installing the following in our bathroom:

http://www.plumbworld.co.uk/0000-16413

and it will be terminated using a one of those roof tile outlets (as I cant access my soffit from the loft) and I am concerned about cold air coming back into the bathroom.

I have seen that AIRFLOW do somthing called a "backdraft flap" that I could fit to the above it in the loft so that it stops airflow from the outside back into the bathroom. Problem I have is that Airflow dont sell directly to the public (or its not worth it just for this one item) and wondered if anyone knows any online or high street supplier for a 100mm backdraft flaps ?

 

[stem]

I fitted a set of these I got from an electrical wholesaler.

http://www.manrose.com/pricelist/019.html

My fan is similar (Wickes) to the one you are installing to which I added the backdraught shutters in the ductwork. I discarded them in the end, they added so much resistance to the ductwork that it almost stopped the airflow as they need a high air pressure to push them open against the spring.

I don't find that I get any noticeable draught though it now though, it seems to get absorbed in the the ductwork somehow. (Mine vents on a gable end opposite the house next door so it is fairly sheltered).

I imagine that with a vertical outlet any wind will draw air from the room like a venturi effect, rather than blow down it. similar to a chimney.

 

[mark.carline]

nice one !

Using that manufacturer and code I did a search and managed to get one of these:

http://www.alertelectrical.com/Extr...lexible-Ducting/100mm-Backdraught-Shutter.asp

I suppose its going to work both ways as I dont want cold air to come in or hot air to go out when the extractor fan isnt in use.

It should also stop spiders coming in - My other half will be pleased ![/url]

 

[JohnD]

If the duct is rising from the ceiling through the roof, it actually doesn't need a fan! (hard to believe I know).

The steam is lighter than air so will rise up like smoke through a chimney
(warm air does it too).

You might get away with something like a hit + miss vent to prevent the warm air being lost needlessly.

I did once have a bathroom extractor with an electrically-operated shutter than opened when you turned the fan on. It was one of the more expensive ones, I think perhaps a centrifugal dimplex or vent-axia?

If you do use one of those shutters that is opened by the airflow, you will need a fairly powerful fan - centrifugals are usually better for that, and also less noisy. there are some designer's tables of airflow resistance per metre of duct that may also have a value for shutters (can't remember where I saw them, sorry, but someone may know).

Edited - I see some of the fans on your link have an automatic iris, which sounds very suitable for preventing draughts and unwanted airflow
http://www.alertelectrical.com/Extr...-Fans/Airflow-Icon-15-Extractor-Fan-White.asp