5" thick wall, 4" extractor fan. To avoid draughts, I want a backdraft shutter. I'm also using one of the Toolstation stainless steel bullnose outside cowls.
Trouble is that this little stack, along with the wall mount extractor, needs a 6" minimum length. I think I need to ditch the metal bullnose (and its long inner spigot) in favour of a shallow plastic cowl on the outside. Alternately, find an outside cowl with a built in backdraft, and that isn't made of rubbish. I don't want the usual outside multi-flap, as they always seem to shed flaps before too long.
The backdraft shutter I've got is the tube-mount one from TLC. Crappy flimsy pivots and a spring I've already replaced as far too weak to hold it shut. As it's two flaps, not three, that's at least 2" of tube length needed.
Why is this stuff never easy? Shouldn't it just _work_ by now? And where's my jet rocketpack?
You might be better off with a window which opens, rather than an extractor fan, precisely because shutting it is a problem.
From the early 70s to late 80s I lived in a house which had an "Xpel-Air" fan fitted into a kitchen window. Yes really. A circular hole had been cut into the actual glass pane, and the fan came in two parts which were offered up from either side and joined together. Not so easy if you have double glazing, of course, but not impossible either.
It had backdraft flaps built in, not as a separate accessory. When the weather was blustery, they kept flapping noisily due to the turbulence causing frequent pressure fluctuations which made the air want to flow sometimes out (which would open the flaps) and then in again (which would close them - PLOP!).
It is never easy because the way the draught wants to go depends on the weather, and the way the prevailing wind interacts with your house. Backdraft shutters operate like diodes (one-way valves), and while they will prevent a draft coming in through the fan, they won't prevent it going out, and if that's the way the air wants to flow, you will still have a draught. You just can't win.
Perhaps you should stick with an ordinary extractor without diodes, and then build a little cupboard around it, well sealed against the wall and with a tight fitting door. Then when you want to operate the fan, just open the door first. You could even rig up a microswitch to the door so that you only need to open and shut it, and not operate a separate switch as well. A bit Heath-Robinson, but that's what DIY is all about.
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