Whole House fans - where can I buy one?

[Pyriform]

I've decided these are a good idea, and I'd like to fit one. The trouble is that the only suitable products I've found using google are from US companies, designed for 110V. Does anyone know of a UK supplier for this sort of thing?

[For anyone who doesn't know what I'm on about, a whole house fan is a fairly powerful fan that vents hot air from the house into the attic space (and thence outside), and draws cool air in through open windows etc. The idea is that you run it when the house is too hot, and the outside temperature is significantly cooler - typically to cool things down at night after a very hot day.]

[Tim Watts]

How about a number of parallel units: axial fan, 4" ducting (rigid where possible, flexi[1] at the end for any fiddly bits?

[1] Can be got in round and rectangular form.

I'm using this method to vent an islanded bathroom to the soffit over the front door (being a straight joist run). If you are only venting to the loft (to exhaust via the eaves) then you'd only need short duct runs to allow the fans to go somewhere sensible and perhaps away from being over the bedroom to reduce noise.

You also have the option to vent via more ductwork directly outside.

I got my ductwork from BES. I'll look up the fan if you like, but they are not uncommon. You can get fairly subtle vents in a number of finishes (white, brown, chrome) for the bedroom ceiling end and soffit end (if required).

[zaax]

As heat rises just leave the loft hatch open and the house will vent naturally, it's green to boot.

[Guy Dawson]

Your google-fu letting you down?

Try searching for

heat recovery ventilation

on UK sites.

Guy

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[Tim Watts]

I don't think he wanted heat recovery (I was about to google, knowing those are available here) untill I read it again...

[spamlet]

Seconded: passive ventilation is even very effective in hot deserts. Better would be to have a fan to pump the warm air back down from the top of the house in the winter than the other way round. Leaving loft hatch open and a window downstairs creates plenty of cooling draught, and a fan would have to be going it some to even keep up.

S

[NT]

Seems most replies arent what was wanted. Beware of venting into the loft, condensation can cause problems. Also you need to provide trapping of dust etc that might fall down when fan not on. However as a cooling method it is, if used only at the right times, very good.

NT

[js.b1]

Do you have a loft hatch door?

1. Create a new spare door with a large Xpelair ceiling fan fitted into it - the very big ones are actually quite cheap (about =A360 or so for 300mm or something like that).
2. Fit a 5A socket near the loft hatch off the lighting final circuit.
3. Fit a battery powered heat alarm if you wish directly above in the loft.
4. In summer fit the "fan loft hatch door", power up, done.

The heat alarm is in case the AC fan were to stall catch fire (Xpelair will be EBM-Papst so will have a bimetallic strip cutout but this cycles on & off so heat can build up quickly).

Realise house humidity will be pushed into the loft, which at night will drop in temperature significantly - perhaps below the dew point of that humid air causing condensation. Hence remove when the hottest days of summer are gone.

Alternatively plumb the thing in properly with aluminium (or fire rated) ducting to an outside vent in a gable end or soffit and a backdraught shutter (otherwise it will bleed heat out when you do not want it to such as winter). If the fan is quiet enough to run overnight (you can get speed controllers) it will really make a difference dropping downstairs temperatures.

[NT]

12" extractor or even a boxed in ceilng fan.

Loft condensation can be avoided by venting outdoors rather than to loft. Loft can have its own fan just to cool the loft, reducing conduction to upstairs rooms Advantage of separate room fans is that each can be controleld thermostatically for best effect.

Do run these things on differential stats, otherwise the overall effect is much reduced. And arrange them to provide heat for part of the year.

NT

[NT]

NT

[Pyriform]

My google-fu is in better shape than your reading-fu.

If I wanted a heat recovery system, I'd have searched for it. I don't, so I didn't.

[Pyriform]

I know about natural convection, thanks.

And I want to install a fan, since forced cooling will be much more effective, on those (relatively few) occasions when I need it.

[Pyriform]

It looks like I will have to bodge something (unless anyone manages to answer my actual question!). The problem will be getting a fan (or fans) that shift enough air - bathroom extractor type fans are orders-of-magnitude inadequate - and yet aren't industrial ventilators!

[Pyriform]

I quite like this idea - thanks. Would be a nice proof-of-concept without making holes in any ceilings. I'll take a look at the Xpelair range to see if they approach the sort of air flow I'm looking for (and which I haven't actually calculated yet!)

[pete]

Wouldn't you only get condensation if the loft (either air, contents or fabric) was cooler than the incoming air? In my house in the summer the loft is the warmest place as the sun heats the tiles, since the insulation is between the loft floor and the first floor ceiling. So venting from the house into the loft will introduce cooler air into the loftspace.

[Tim Watts]

Some of those inline fans can shift a fair volume - don't think "bathroom" necessarily, think "inline fan" - the question is, how much do you want? I've never been impressed with bathroom ventilation so I got a higher rated inline fan for mine.

Ultimately, there's only so much you can shift up a 4" duct and vent (unless you were planning to put more or larger vents in each room?).

Regarding homebrew, if you could get a bigger fan, making a distribution box out of ply and lined with acoustic dampening with 4" spigots wouldn't be too hard, with the fan inside to cut down noise. I wonder if googling for 6"/150mm fans would lead to something...

Regarding readybuilt, there much be something in the 6" area. I'm thinking offices where the loos have several 4" vents and ducts feeding into a 6" or bigger duct with something (which I never saw) on the other end.

[Pyriform]

It could be an issue if the night is very cold (and the loft is insulated only at floor level). For what I have in mind, I don't envisage there being a problem.

[pete]

Some years ago I bodged up a forced-air vent from the first floor out through an open window. I used a 15" fixed fan, some flexible metal ducting, cardboard and duct tape. The cardboard / tape was to make a funnel over the fan's outflow to direct air along the duct, out of a nearby window. It did have a noticable effect on the heat in the house, but caused a lot of vibration which resonated and was nearly as annoying as the heat.

[Tim Watts]

I don't think that would be a problem - the loft structure is hot so no risk of condensation.

Given the OP's stated use (cooling a hot house in summer) I don't think even the risk of introducing a little extra humidity that may condense in the cool wee hours is worth worrying about either - it will clear the next day. Wood rot comes from sustained condensation, not a bit once in a while.

The only risk I see is running such a system in the winter - that would be bad, so I suggest making provision to lock it off.

[Pyriform]

Fair point. I haven't calculated how much air I need to shift yet. The US DOE has some guidelines, which some US whole-house fan makers think are a bit high, so I'll do some more research and some sums and then revisit inline fans. The ones I briefly looked at didn't come close to the airflow of the US products.

I'm rather liking another poster's idea of making a special loft hatch, with a big fan venting directly into the loft space, at least to start with. Ducting and multiple inlets might come later!

Thanks for your ideas.