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Joined: Jul 2002
Posts: 8,432
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Trumpy Offline OP
Hi Guys,
I was at a new house today and was asked a rather strange (but not in itself silly) question by the guy that owned the place.
Now don't get me wrong, I'm not a building inspector by anyone's stretch of their imagination, but this question had me a little intrigued.

What it pertains to, was the guy was asking if installing a fan (like an Expelair) directly in the ceiling lining in his hall-way, would contravene the Building Act, with respect to moisture transfer?

Now, ever since the "leaky homes" debacle came to light over here, it has been almost a sin to make openings in plaster-board walls and ceilings, even down-lights need to be of a certain rating for different areas.

The reasoning behind this idea, is the fact that even during winter, with the corrugated steel roofs we have over here, these is a LOT of heat generated in the roof void, that often goes to waste, on the other hand, New Zealand has some of the dampest houses in the world, owing to the climate and the fact that people never open their windows anymore.

The idea would be to install one or two of these fans, to pull down heated air out of the roof void to combat the colder, damper air in the rooms below.

This in itself isn't such a silly idea, however, I'd like to bet that the Building Act has some sort of a fish-hook clause that prevents this.

Your thoughts on this "idea", please? wink

Joined: Mar 2005
Posts: 1,803
Hi Trumpy.

I haven't posted in a long while, though I do pop in occasionally for a look....

This looks like a job for a 'heat recovery mechanical ventilator'. This is a unit with a crossflow heat-exchanger and circulating fans, ducted to expell stale air and bring in fresh air to the house. Heat is transferred from exit to input air, so the unit economises on both heating or air conditioning. I have a Greenwood MVHR 78 installed in my loft, which I suspended on ropes for silencing. There are lots of other makers, BTW.

Data Sheet

It 'makes' about 1.5kw, is claimed 90% + efficient, is totally silent, switches out to extract only if the input air approaches freezing and has a condensate drain-pipe which I plumbed out to a rain gutter. It also has a filter bank and is easy to duct with 6" [150mm]diameter flexible. Flow Control is adjusted in the machine, to set the amount of air, by tappings on a transformer. The switching allows normal flow of air, boost, or extract only option. We never turn it off, it only uses 100W.

In your application, provided the loft air is clean and safe, [ and I mean by that no risk of chimney flue leaks, stench pipe air from bathrooms, legionella risks from water tanks, grease from cooker hob/oven venting etc.] and you have good eaves ventilation into the roofspace from outside, I see no reason why the inlet to the machine should not draw loft air direct, provided it is on the roof side of the ceiling insulating quilt. The inlet and exit on my machine go through the slates to outside via domes. Inside air is drawn from rooms by 4" adjustable flow ventilator valves, inserted into the sheetrock by snap action, air 'in' is by 2 off x 6" diameter valves.

I think I paid about 900 Euros, and with the price of fuel rising.... Hope this helps.


Wood work but can't!
Joined: Jul 2002
Posts: 8,432
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Trumpy Offline OP
Don't think for a second that anything you say doesn't help, I just wish you'd give more input here.
I've read your reply to my thread and have taken them on board.
Young people call folks like you "Old Skool" (yeah spelling has dropped in the last few (15) years), old school has the best ideas on how to save money though.
Live through a war, sonny.
Alan, I'll pass the ideas on, it has to be better than a passive fan in a plaster-board ceiling.
And again,

Last edited by Trumpy; 02/03/09 07:44 AM. Reason: Typo

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