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.

Alan



Wood work but can't!