Welcome! Will that duct go from ground to first floor? What about fire regs? Intumescent liners at floor penetration? Think we have discussed this before. Anyone remember where?

Posted By: barge17In both houses we are going to install short air ducts to tranfer heat ( only when required ) from a space above the wood burning stoves to the coldest point in each house using 6" ducting

Where is this "coldest point"? Is it inside the thermal envelope? If so, why is it cold? Does it need more insulation / better glazing? Or do you just mean that it's unheated?

As a rule, air is not the best means of moving heat around. Water has a much higher volumetric heat capacity & doesn't risk moving smoke around. If the wood burning stove is too big for the room then better to choose a smaller one or one with a back boiler which can pump excess heat to the thermal store used by the gasifying wood boiler.

Whichever way you do it, choose a stove with an external air supply input so that you don't need airbricks in the room.

David

If your one mains gas, go with that. It is hard to beat economically and environmentally.

OK Joe. You'll be fan-assisting that movement of air will you?

Posted By: JoinerOK Joe. You'll be fan-assisting that movement of air will you?" aria-posinset="0" aria-setsize="0" hspace="0" alt="" vspace="0" loop="1" src="http://www.greenbuildingforum.co.uk/newforum/extensions/Vanillacons/smilies/standard/wink.gif" ismap="false" width="15" start="fileopen" height="15" >

No, actually. Not done the maths(I will leave this to ST) but had planned (on the back of a fag packet) on a large duct a bit like the old air heating duct at a high level within a inglenook type fireplace and a return duct of similar size at low level so the air flow was passively driven by the heat from the stove. This would also give the opportunity to create a door on the duct to stop the flow if required.

I have no idea how much smoke you need until it becomes dangerous, but smoke and fire detectors can be wired in to shut down fans and automatically close vents. More work involved, and something that only gets tested in a real life situation once.
A lot of the risks of fires/smoke have been removed over the last 25 years (since that dreadful Woolworth fire), and Joiner can get hold of many examples of things that have happened since, but I am sure he will agree that having things that do not smoke/burn in a house is the first and best route to take.

The sums to work out the the transfer of smoke in a house are quite simple, they are just the ACH really, the path the smoke takes is a lot harder to establish. Reduce the leakiness and the flames have less oxygen to work with (how fire doors work). But this may mean that there is a higher concentration of toxins released from something smouldering and producing less heat. What would be interesting to find out is the number of small fires that go undetected for a relatively long time compared to short fires that are detected quickly and compare them to the type of building and the services that building has. A nice little stats job for a part time fireman there.

Have I just been quite sensible there, must be an inherited thing as my Father was in a house fire when he was a kid and still talks about it now, 82 years on. He used to take us past the charred plot where his old house was in the 1960's. Can't see a plot on West Wycombe road laying empty for 30 or 40 years now these days, a new meaning to 'brown field', black field more like.

Ha ha. Nothing like keeping it simple.

Now back to the OP (as they have been reading this site for a while I hope they have a sense of humour)

Insulate, airtightness and then look at the best system for your money.