Do you have a heating figure in terms of kWh/m2 p.a.? What sort of figure do you think you can put on 'very airtight'?

If you get very close to 'zero heat', at least a good proportion of the time, do you really want a big lump of thermal mass connected to a passive stack vent to strip heat out from the house when the stove is not lit? A.dd to that the concerns re pollution, and of course the capital cost, and maybe you 'don't want' a stove at all..

Re external air supplies, I was very much in favour of these till I found that at least one manufacturer's kit has inherent leaks in that the duct simply isn't airtightbetween the external wall and the stove wall. Choose carefully.

Posted By: ComeOnPilgrimSAP have put the kWh/m2 pa as 31.5.

The SAP calculations have put 5m3/h/m2 as the air tightness.

5 m³/m²/hr isn't 'very airtight'. If you are intending to build a lot tighter than that, so you are very airtight, then you need to run the thermal model with something approximating the actual airtightness to get a realistic heat demand. You may be in the realm where PHPP gives more reliable results than SAP.

I took the figures from the SAP calculations as I did not know what a reasonable score was. Hopefully I'll do better.

I'd still be interested in any comments on my original questions if anybody has any thoughts?

Posted By: ComeOnPilgrim1. What's the real benefit of a triple wall chimney? Could I not just get a double wall chimney and have a different pipe bring the air to the stove?

That would be my solution - and what we did with 2 stoves. I seem to remember being worried that the counter-circulating air would cool the exhaust flue (despite presumed insulation) and cause tar build-up in the flue. We have had no problems with an external air supply pipe causing leakage.

2. I was previously thinking that the chimney would go through the ceilings and the roof, but this is quite problematic as the joists do not line up on the 1st and 2nd floors, and then there are the rafters on the roof. Could I not just go through the external wall and up the outside of the building?

Would this require planning permission? If you can do this, it would be my recommendation to do so otherwise you'll need to place your stove according to one set of joists and then potentially have a dog-leg to straighten it up through the roof apex - assuming you have a normal chimney. If you have a masonry chimney on your plans, you'll need a way to support that also as you can't hang it on twin-wall flue! Obviously, you'll have the visual impact of a flue to think about, but you'll know that better than us.

As others have said here, and this pains me to say it as I love (or did love) our stoves, do you need it? We can hardly use ours, it makes the rooms they're in unbearably hot but the heat doesn't circulate well through the rest of the house so we're roasting in one room, with the window open in negative temperature conditions and other parts of the house potentially have thermostats calling for heat from the UFH! If you are well insulated and air-tight as you like, you might not need it or importantly be able to use it so is it worth the hassle. I've photos somewhere of all the hassle we needed if you want to think about it more...

Firstly i would question how attractive a 3W flue will look as ducts its way around the fire to feed the air supply which are usually underneath the appliance, what sort of contraption is affixed to your new stove?

secondly a quick look Approved document J will detail the flue designs for passing through an exterior wall there are messy and complicated with soot traps and access doors, hard to make look nice as a retro fit especially in a new build.

i would use twin wall up through the house making use of the residual heat in the rooms as it passes through them, and core cut a neat hole through the back of the chimney niche for the air supply duct(if its needed) my understanding is below 5kw would not require vent

Posted By: DarylPCoP, yes... 5m3/m2h is average. Aim for sub 3 at the max.

Mode - no. Mean - no. Median - no. Dream on!

And the shame is it isn't even particularly good, as above!

Posted By: an02ewi would use twin wall up through the house making use of the residual heat in the rooms as it passes through them

Will it be residual heat or residual cooling? If the fire is mainly lit then there may be some useful residual heating. If its mainly not lit (like most fires in the UK) then you might be cooling the rooms 364 days of the year and only heating them on Christmas Day. In this case it would be better to go out through the wall at the earliest opportunity.

David

I've just got off the phone to the designer of the stove we're thinking about! He says that the direct air supply is not totally airtight in order to avoid since problem where there is a risk of carbon monoxide coming into the room where there is a sudden drop in pressure. I can't say I understand completely why a direct air supply that is airtight does not address the problem, but he's sent me a leaflet about it, so I will post more when I get it.

hmm interesting, looks like marketing flannel....
I know for a fact that PH -certfied WBS and BBC-compliant french WBS are room sealed, in the same way a gas combi' boiler is. The combustion air is ducted in from outside 100%.
I cannot see where the sudden drop in pressure would suck combustion products into a room through a sealed stove door?

... no, most are definitely not sealed. But, some are!

Here are some more details that I've found online including an email from the same guy I spoke to: http://paultestaarchitecture.co.uk/2013/06/stoves-in-airtight-houses/