On days like yesterday which are cold but sunny my loft gets quite warm, much warmer than the unheated house because of the thin asbestos cement roof sheeting which heats up in the sun.

I was thinking of the possibility of using thermostatically controlled ventilation to draw warm air out of the loft and into the house.

What do you think of the idea? Some have said it wouldn't be worth it but I reckon it would be easy to set up ( I know how to rig up temperature controlled fans etc).

Although it is is warm there is not nearly as much heat up there as you might think.

Posted By: jms452The principle is fine but there is one word in your post that makes me think that the loft might not be the best place to draw your air from...

As long as the asbestos is in good nick there's no risk.

Posted By: tonyAlthough it is is warm there is not nearly as much heat up there as you might think.

But if it's thermostatically controlled it would only move the air that was above the temp in the house. So it's sound in theory. The main issue to my mind is rigging up the fan/duct in a way that wasn't a cold bridge and therefore a net heat loss.

As to whether it'd be "worth it", it's probably pretty marginal, but why not have a go?

There have been a couple of trials in Glasgow of bringing air under slates through the loft to ventilate the stair well, needs a small fan and bits of ducting. The stair well is an unheated space so there are none of the issues of thermal bridges mentioned above. Colin Porteous has written Papers (and I think books) on its effectiveness.

I wouldn't use it for a heated space in Glasgow as we don't have the right conditions very often and the heat loss is certainly greater than the marginal heat gain. This passive heat gain can also be captured more efficiently through well designed windows.

Cheers
Matt

Sounds like a true solar passive design with large glass atrium on southside

It is easy to make your own version of the Nuaire Drimaster - a fan, filter intake and differential temperature controller (the most expensive bit).

The Drimaster (and vent-Axia copy) were simple, effective and reliable - ergo great bits of kit, but although they claimed to save fuel by de-stratifying the warm air lurking below the ceiling, I did have my doubts on that.

In our first installation, the air coming in was always cooler than the house itself. Ventilation, yes, great. Defeating mould, yes, ditto. Even Radon dimunition by pressurisation. But heat gain from a poorly-insulated loft? Money better spent would be to insulate the loft or roof itself methinks.