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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    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.


    - 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.)
    I would pursue the direct air feed a bit more if there is any way.
    • CommentTimeJan 25th 2021
    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.
    Posted By: greenfingerFrom what I've read, this needs to be 23mm x 23mm for square, or 26mm diameter if round.................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?

    It is not as simple as dividing 26 by the number of holes. You need to divide the AREA of a 26mm dia. by the number of holes and then work out the diameter of the smaller holes from the area of those holes. And probably add one extra small hole to count for increased resistance.

    But as above - do your best to get an external air feed because you really don't want that sort of hole in your wall.
    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?

    • CommentAuthorGreenPaddy
    • CommentTimeJan 26th 2021
    area = 23x23 = 529mm2

    1 hole = 26mm diam

    2 holes = 20mm diam

    3 holes = 15mm diam

    This is the free area, so grilles and mesh will reduce that free area. If you put a grille or mesh with 50% free area (say), then you'll have to double the area of the hole.

    I'd find the grille, mesh, pipe liner solution that can be easily purchased, eg standard pipe with say 25mm exterior diameter. What fitting can go on each end so that it looks acceptable, then make the hole size to suit. If you drill the holes, then try to get something to suit, you'll have backed yourself into a corner.

    Something like this??


    these have 19 holes at 3mm diam, so the free area of each grille is 134mm2. You need 529mm2 total, so would have to fit 4 of these. One each end = 8, and these come in a pack of 10.

    4 lengths of 25mm water pipe, job done.

    Don't at all like the idea of deliberately creating a cold draft, but you asked for a solution to your question.
    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 !
    • CommentAuthorMike1
    • CommentTimeJan 26th 2021
    Best bet would be to sell the wood stove...
    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)
    • CommentAuthorjfb
    • CommentTimeJan 26th 2021
    Find a 5kw burner?

    Though maybe you have it already - I haven't read the whole thread.
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