Motorised damper for extractor fan

[Radian]

I've yet to see an intermittent extractor with a damper to close off the exhaust vent when not in use. Being intermittent, i.e. on a light switched timer, there's a clear 100mm path to the outside world for the vast majority of the time. Being surrounded by centrally heated rooms on all sides, our downstairs loo hasn't got a single outside wall yet it's always the second coldest room in the house. The extractor duct is run up through a boxed-in section in the adjacent utility room and exits near the back door alongside the extractor vent for the utility room - which is the coldest room in the house! It's blindingly obvious that it's the unwanted air exchange between these two rooms that is responsible. I'm reminded of this as the heating has yet to come on and while the house is staying passively above 20^oC , the loo and utility are pretty much at average outdoor temperature - currently around 14^oC. I've also commented here before about how after sanding a painted picnic table outside the back of the house, I came in to find an even layer of dust on the lid of the toilet and cistern that wasn't there before I started sanding.

 

What I feel I need is a motorised damper similar to this kind of thing:

 

 

But ideally it'd be integrated into the outdoor vent as there's no access to the ductwork other than by taking down some of the ceiling.

 

What bothers me is how such an apparently simple thing doesn't seem to be catered for by the manufacturers of ventilation systems. Intermittent ventilation has its place besides DMEV and the like, when general airtightness is already too poor to warrant anything else.

 

Edited September 24, 2022 by Radian

[Mr Punter]

I have the Airflow Icon fans that have an iris type shutter built in.  I also use external vents with a flap type shutter.

[Radian]

20 minutes ago, Mr Punter said:

I have the Airflow Icon fans that have an iris type shutter built in.  I also use external vents with a flap type shutter.

Thanks for pointing me to those. Didn't show up in searches for motorised vents although I'm rubbish at search terms. Flap shutters are the obvious answer I was waiting to be hit with - but they're too restrictive at the end of a long duct and also make an annoying racket when windy. The annoying thing is we're very happy with the extractor as it's got a nice chrome design with built-in illumination, and since I modded it with a PC fan, is almost silent. Still, it's good to see some more options.

[Radian]

A thermal picture paints a thousand words. This is the Utility room showing the ceiling extractor in the corner and the path of the duct located in the space between joists on its way over to the extractor in the loo:

 

 

And the stacked outlets in the porch area outside:

 

 

I could try replacing them with gravity flaps but I'm not happy about the idea of them.

[S2D2]

The best I've seen recommended are the Iris fans or a basic sprung shutter such as https://www.tlc-direct.co.uk/Products/BG4BS.html

 

Mounted towards the outlet it should have an advantage over the iris type (no cold air circulating the length of the duct above the ceiling) but I'm yet to see anyone state they've used one to good effect, plus I always assume pressure driven mechanisms will be noisy - outdoor wind can still open it. Interested to see what you come up with given you can monitor the change with the thermal camera.

[Radian]

2 minutes ago, S2D2 said:

The best I've seen recommended are the Iris fans

Actually, the ideal would be an iris that could have its direction of airflow reversed - then I could mount it on the outside (it's very protected up there) - at

least for the toilet extractor to make a push-me-pull-you. I suppose it could be boxed in ar$e about face outside but that'd probably end up being fugly.

 

The utility room  could be done with an iris the right way round inside but even the short elbow to outside is a cold bridge unless also damped outside.

[Radian]

Addressing the extractor in the utility room, discussing the matter with SWMBO has resulted in an alternative solution:

 

 

100mm thick plug of rigid PIR. It transpires that the last time the extractor had significant use was probably in the latter part of the 20th century. The tumble dryer is a condensing one and in the Winter there will be a dehumidifier to assist with clothes drying. Anyway, this is an experiment that's easily reversed if it proves problematic.

[S2D2]

On 27/09/2022 at 11:22, S2D2 said:

basic sprung shutter such as https://www.tlc-direct.co.uk/Products/BG4BS.html

 

I installed something like this as an experiment at the insulation layer of a duct run and unsurprisingly it makes an annoying noise when it's windy outside. I will move it to after the inline fan and report back if it's still a nuisance. Sadly a 100mm pir plug is not suitable, no matter how effective!

[Radian]

I've still not addressed the upper vent. The first cold snap will probably spur me into action. But the utility room feels much better now, a combination of gap filling around pipes to the outside wall and stuffing rockwool in and around a boxed-in AAV that also connects with the ceiling void where the extraction duct for the loo runs:

 

 

The box spans from floor to underside of upstairs floor with the AAV coming half way up to the access hole. I filled some bin liners with rockwool and pushed them in and up through the little letterbox.

[dpmiller]

Looking at the way that flexiduct is strained, I wonder if it's worth re-doing that properly while you're in there?

[Radian]

Only got that 200mm wide slot to work through - I'd have to tear down the top of the plasterboard box to get to it properly. It's only got plaster splashes on it. Admittedly it's not laid in particularly neatly but it's not my handywork.