Hi all

Sorry to be hogging this sub-forum!

I'll be having a 6kW wood stove installed soon. It's an old house, so we get the first 5kW for free and only need to provide air for the remaining 1kW. From what I've read, this needs to be 23mm x 23mm for square, or 26mm diameter if round. We don't want any large grill faces or anything like that. Would prefer it to be visually as unnoticeable as possible. Can't do anything with the window, as that's being replaced in the future.

So...

- Would it be best to do one hole to spec, or several little holes?
- Can anyone work out what size the little holes would need to be if doing a few? Or is that as simple as dividing 26 by the number of holes?
- My installer said it would be enough to just have the holes lined... Any ideas what's best to use?
- How to make the holes rodent mouse proof?

Also, I've read several times how random the nominal rating of stoves is... How 5kW stoves can be largely different in physical size, have different sized fire boxes and therefore different fuel loading capacities, have different ranges (the Arada Ecoburn is rated 1.5 - 9Kw, whereas the Clearview Pioneer is rated 1kW - 5kW)), and yet all be rated as nominal 5kW. And on top of that, how the testing of stoves is very artificial and easily manipulated to reach a desired rating. With all that in mind - and forgetting HETAS, regs, etc for a moment - how much real life need is there for an air vent with a 6kW stove installed? For the record, the stove is a Woodwarm Fireview 6kW (5.8kW nominal to be precise).

Many thanks

(PS - We'd love to have a direct air feed but for several reasons it's just not possible.)

If you do chop a big hole in your wall, or multiple small holes then you can rodent-proof it with some strong steel mesh over the opening(s). You might want insect mesh as well. Don't forget that in winter there will be cold air coming in so (a) make sure you can cope with the drafts and (b) make sure there's nothing that can go mouldy or rot nearby (e.g. soft furnishings).

As Dominic says, try very hard to fit a direct air feed.

Many thanks for the replies.

RE direct air feed. The walls are thick, the floor is solid, the stove will be in a recess which is not on an external wall... There was just too much involved in getting air to it. It's too late now anyhow as I don't think the Woodwarm Fireview can have a direct air feed, and we've already ordered.

@djh - thanks for those suggestions; very helpful. Guess I'll have to figure out how to fix the mesh to the wall, something I'm not too sure on. Nor what exactly I need to use tbh.

@Peter_in_Hungary - that's very helpful, except I'm useless at maths and so it has just got me scratching my head! Anyone know how to do this with numbers?

Cheers

If you are stuck with the holes in the wall I give it 1 week of cold weather and you will cap of the air intake (AKA hole in the wall) when the stove is not alight so perhaps design this in from the outset.

I once saw a report that showed that for an open fire place with fire lit 8 hours a day the net heating effect was negative - i.e. more heat was lost up the chimney when the fire was out than heat gained when the fire was alight. Whilst your holes will not be (quite) as bad as an open fireplace I bet you will notice !

I would rather have a pipe in the room than a hole in the wall.
I am actually considering this in the other room (the room that has the air brick, we don't use that room in winter because it is so cold)

Rules are for fools and the guidance of . . . . . . .

It's an elderly thread - like me - but I thought new readers of it might like to hear my experience.

In short - big old farmhouse, 6 bedrooms, 3 identical Franco Belge MB stoves in rooms at each end of the house and one in the middle. Solid walls and 250mm fibre-glass in the roof. New-ish DG windows throughout, 4 very old, rather draughty doors (very draughty in windy weather hence heavy curtains and 'sausage dogs').

The WBSs feed into original chimneys, the first was installed before any reg's were in place. No venting, flue or anything. It's great, runs 24/7 and gives off enough heat from its central position to warm much of the house most of the winter, including the 1st floor. Thin logs burn quickly giving off most heat, big logs (10" diameter) go on at midnight and are still ticking over at 8am. Burn heavy, dry wood - ash is best.

For times when more heat is required I turn on the GSHP with UFH to provide a base level of heat which would equate to the temperature of the unheated house in Spring /Autumn.

The second and third WBSs are lit when family or friends stay and more of the house is occupied. Both of these were installed with expensive SS flue liners, as per HETAS regs, but before any requirement for venting. These two function no better than the first, need sweeping no less often (but still only once per year in the summer) and, like the first, are an absolute joy to use.

Remember to plant as much timber as you burn or, if buying it, check that the seller is doing that Also that wood rotting on the ground releases its embodied CO2 just as burning it does and, though burning clearly produces particulates, current clean-burn WBSs are a bit like cars with DPFs or catalytic convertors - fairly to very clean.

John,
The twinwall I know doesn't supply air to the stove like a gas "balanced flue" twinwall where input and exhaust are both run up the chimney, i.e. one pipe inside another?
Is the biomas twinwall you describe some kind of new product? If so does it require a different sort of WBS.

Maybe I've misunderstood the thread.

I think this may be the type of thing RJ is referring to. Been around for quite a long time, but I've never needed to use it, always find another route for direct air feed. Retrofit in the middle of a house with a solid floor would be a great use.

https://www.poujoulat.co.uk/solutions/residential-applications/chimney-systems-for-residential-applications/twin-wall-insulated-chimney/efficience

Ah, I guess it's a case of terminology usage. The "twin-wall" I think of are spiral wound, SS, uninsulated, flexible. and generally installed "not seen". The polished SS rigid type of insulated twin-wall stuff I have on my own WBS.
I've fitted the gas heater uninsulated balanced flue liners some years ago but I was unaware of the same principle used for WBS, but it makes sense.

The difference appears to be that the twin-wall has a 1" ring entirely full of insulation, whereas the triple-wall has a thinner thickness of insulation separated by an additional concealed ring of metal, creating an empty chamber.

I was looking at one of the sections pictured somewhere - I thought in one of the links. There was no scale however, so it was hard to tell whether the whole thing was wider than the twin insulated, or simply a division within the basic twin to split the insulation layer into thinner insulation plus air gap within the same dimensions.

I understand the principle of supplying the air to a stove from a chamber within the flue itself, no problem there.

As I said before I've used the same "balanced" principle of one upward exhaust tube and one downward air feed all enclosed within one flue liner. I used it when I installed a very smart and very expensive "hole in the wall" remote controlled gas fire. However the internal architecture of the machine itself was designed around the vertical balanced flue principle.

Q. are similarly operating WBSs so designed, I can't see how a bog standard appliance would work unless it is?

I guess it all depends on whether the OP posts stove has a rear air intake.