Fan ventilation - in or out?

[jgharston]

I'm planning on installing a fan to create an active through-draft through the house. Should it be mounted to pull air into the house or pull air out of the house?

Ta.

-- JGH

[auctions]

Pull air out. If you pull air in it will be a concentrated patch of cold air. If you pull air out it will be replaced through loads of tiny drafts, and the coldness will be distributed.

A

[Rod]

My brain immediately says 'neither' - or maybe 'both'.

If you have positive pressure that will tend to help keep dust levels lower by pushing air out.

If you have negative pressure that will tend to draw air, and hence dust, in.

In either case, if the pressure difference is significant, you might find opening/closing doors and windows becomes, umm, interesting.

My brain says, have two fans, one pushing in and one sucking out - balancing each other. If anything, a slight positive pressure.

My brain is probably broken by trying to cope with 30C. :-)

[Mike Barnes]

However you mount it, it will do both. Air will either flow in through the fan and out through open doors, windows, and other apertures, or the other way round.

I think the main issue would be the outside air coming in - you'd probably prefer not to have that concentrated near the fan. So "out" would be the best choice.

[Andrew Gabriel]

Probably want to exhaust the air on the upstairs side facing the sun, and the coolest air to draw in is likely to be on a downstairs side away from the sun or north facing.

In the summer, I replace my loft hatch with one which has a

10" vent-axia extractor fan, which serves both to extract the hot air from upstairs, and to help cool the extremely hot air in the attic.

[ARWadworth]

Let me check I have got this correct.

You have a 10" fan in the loft hatch to blow air (from the landing I presume) into the loft. This sounds OK for my house. Did you need to make any extra vents in the loft?

Adam

[Andrew Gabriel]

No - it's got vents around the soffits. It would probably work much better with a vent at the apex, but there isn't one and that would be hard to implemnt.

The original aim was to keep the loft cooler, and it probably manages to knock some degrees off. It was 36C up there today at 2pm -- it would probably have been something well over 40C without it.

[Michael Chare]

Maybe it depends on the location. An extractor fan in the hall might draw smells out of the kitchen and loo, and damp air from the bathroom,

[The Natural Philosopher]

Definitely ;-)

[jgharston]

That was what I was thinking of.

Hmm. There's an idea. My cellar is always noticable cool, even in the heights of summer. I could do something to draw that cold air into the rest of the house - passive air conditioning :)

-- JGH

[Owain]

Or you could just take a deckchair and portable telly down there ...

Owain

[Martin Pentreath]

Good idea. Our cat has taken up residence in the cellar in protest at the hot weather. Just be grateful that you haven't evolved with a black fur coat instead of sweat glands.

[Huge]

Why?

[chrisj.doran]

Get a reversible one so that when you're there alone you can sit in the cool breeze, but when the house is full of people (or smoke from the cooking) you can spread the sucking around.

Chris

[Andrew Gabriel]

I have some electronics up there relating to home automation. Also, after a few weeks of hot weather, the cold water tank becomes a warm water tank, even though it's lagged. Also, even though well insulated, it seems to generate heat radiated from the upstairs ceilings.