powered backdraught damper

[sm_jamieson]

Just fitted the bathroom extractor - vent in ceiling, fan in loft, with a h umidistat and all is good. I have two backdraught dampers, a gravity one in the vertical section and a sprung one in the horizontal section and there are a bends in both planes so no direct route for wind. There is a slight c oldness around the vent and external noise can be heard which is not surpri sing. However it made me realise what I really want is a powered damper tha t seals in an airtight manner. Googling does not find much. Any ideas of where to get one, or how to make one, for a sensible cost ?

Simon.

[Andrew Gabriel]

Search for extractor fan with shutter. They aren't cheap.

I have a few, but they're old. A 6" Vent Axia which has solenoid operated shutter, which operates with quite a loud bang at both switch-on and switch-off. A couple of 4" Deta extractors which have thermo-electric solenoids which open and close very slowly (and silently) as the solenoid self-heats and cools. Note that as thermo-electric solenoids take a few minutes to close after the fan is switched off, you can get a backdraft for a short time.

Neither of these products are still around (Deta themselves folded some years ago, sadly), but you can find fans with powered shutters.

[sm_jamieson]

a humidistat and all is good. I have two backdraught dampers, a gravity on e in the vertical section and a sprung one in the horizontal section and th ere are a bends in both planes so no direct route for wind. There is a slig ht coldness around the vent and external noise can be heard which is not su rprising. However it made me realise what I really want is a powered damper that seals in an airtight manner. Googling does not find much.

It was an inline ducting damper required. The through-the-wall fans might b e better than they used to be, but I always remember my mum's one rattling away.

Something from the US,

Looks fairly basic so I'm not sure how well it would seal - airtight is the aim, to avoid noise transfer as well as better immunity from draughts. I guess such things would be available from aircon suppliers in the UK, but the "HVAC" industry is of course much larger in the US.

Simon.

[Chris Hogg]

Googling for air duct dampers uk brought up this

or more generally,

[Harry Bloomfield]

sm_jamieson presented the following explanation :

The one we have in our bathroom extractor fan is fairly airtight. It operates via a wax cartridge expanding, when heated. Rather like the waxstat thermostat they sold for car cooling systems.

It has an electric heating element, to heat the wax, the cartridge expands, pushes on a sprung lever to open an iris type shutter arrangement as you used to see on cameras. It takes around 30 seconds to fully open, from fan switch on, then a couple of minutes to re-close after switch off. Wax expansion is a very powerful force.

The other type of extractor shutter arrangement, uses a solenoid, which makes a loud bang as it opens and closes. The wax type is almost silent.

[Harry Bloomfield]

Andrew Gabriel laid this down on his screen :

It is not a solenoid, it is a wax cartridge which expands and contracts when heated and cools.