Heat Recovery Ventilation systems and wood stoves

celerity

I am looking into MHRV systems for our bungalow.

In our south-facing lounge we have a wood stove which gets its air from the room (i.e. we have an airbrick a few metres away from the stove, it does not have a dedicated air inlet pipe from outside).

I'm sure I've read on the web that this setup prevents us from using an MHRV system for the lounge, but I phoned up a company and they said it's not a problem. They basically implied we would seal up our airbrick as the MHRV system would make it redundant, although I'm not sure that would meet with building regs...

What I'm hoping MHRV would do for us, is to help heat our north facing rooms, which are noticeably colder than the south side. i.e. I'd like to have a system that could take air from the warmer rooms and pipe it into our colder rooms. At the moment going from the kitchen to a bedroom is like traversing several timezones, it really is a big temperature differential .

Additionally, I'd like to be able to utilise our wood stove flue in this system, so when we're using our wood stove, I'd like to be able to flick a switch and turn on some kind of heat exchange connected to the exterior of the flue in the loftspace, to regain some of the heat.
Is this feasible? I can't find any such system on the web, and the company I spoke to had never heard of it either. Have I potentially invented something useful(!) or is it a pointless idea?

I'd also be interested in any general thoughts on MHRV systems - do you have one, do you run it 24/7 and is it worth the initial outlay and running costs? I was told they typically use DC motors drawing about 40W, so that is about 1kWh of electricity a day. Does that sound about right?

Cheers,

/\dam

RenovationMan

We have a MHRV in our granny flat and it takes heat from the kitchen and batchroom and channels it into the bedroom and living room. It doesn't provide heat though as it's main purpose is to provide fresh air.

As far as I can make out logically, if you had a 100% efficient unit with internal air at 20C and external air at 5C, the air from the MHRV would be warmed to 7.5C. As MHRVs are at best 90% efficient the heat output would be even less.

You can get MHRV that have internal heaters, but these are obviously powered by electricity and so may be more expensive than gas or solid fuel.

You generally have the MHRV intakes in the wet areas of the house (kitchen/bathrooms) and the outlets in the livingroom & bedrooms as it helps get rid of condensation.

As far as your wood burner is concerned, I'd suggest buying one with an external intake instead of the having an air brick as the air brick goes against the point of having a MHRV in a sealed house. If the woodburner is room sealed then there shouldn't be a problem with having a MHRV outlet in the same room as the stove.

jamesingram

some info here
http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=6299&page=1#Item_0