Sun, 30 Aug 2026 08:53:40 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18050&Focus=304599#Comment_304599 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18050&Focus=304599#Comment_304599 Thu, 14 Dec 2023 16:22:36 +0000 greenfinger
I've got a wood burner installed in a builder's opening. Single wall flue into a flexible chimney liner. The thin steel closure plate is higher than the lintel in front - i.e. you can't see it when stood in front of the stove. I therefore often wonder how much heat gets "trapped" in that pocket of space behind the lintel, and subsequently escapes through the closure plate into the chimney void.

So I've been thinking about insulating above the closure plate using mineral wool and wondered what people think to the idea? I've not come across much info of people doing that. Seems sensible to me but perhaps I'm overlooking something.

I did mention it to the chimney sweep when he was last here and he was against the idea. Not sure how much I trusted his opinions though (on that and other things!). One of his concerns was the mineral wool combusting. I told him that in my limited knowledge it's not combustible but he wasn't having any of it!

Any thoughts?

Many thanks]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18050&Focus=304600#Comment_304600 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18050&Focus=304600#Comment_304600 Thu, 14 Dec 2023 17:30:11 +0000 Dominic Cooney I don't see any problem with mineral wool, it isn't flammable.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18050&Focus=304602#Comment_304602 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18050&Focus=304602#Comment_304602 Thu, 14 Dec 2023 17:34:40 +0000 tony https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18050&Focus=304605#Comment_304605 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18050&Focus=304605#Comment_304605 Fri, 15 Dec 2023 07:51:20 +0000 philedge
An insulated and therefore hotter flue accumulates far less soot and doesn't need sweeping anywhere near as much. Our liner is uninsulated up till first floor ceiling height and insulated thereafter and we have no soot whatsoever. I sweep the liner every 3-5 years and get maybe a third of a builders bucket of light grey Ash out of the flue and top of the stove. We run the fire hot and only burn well seasoned wood but couple those with an insulated/hot flue and the flue stays clean for years.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18050&Focus=304733#Comment_304733 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18050&Focus=304733#Comment_304733 Sun, 24 Dec 2023 12:40:34 +0000 finny
Almost all mineral wool on the market contains all sorts of stuff you would not expect. Some of it combustible, others just break down into nasties when they are heated. If you do go down this route you need the Rockwool product used in the marine environment, for some reason that stuff is ok, but it costs a fortune..
Check data sheets to be sure.

I know this goes against the grain of what most people on this forum are aiming for, but insulation in the chimney cavity, ie outside the liner, but inside the breast, is liable to cause serious problems with damp down the line. Unless you happen to live in Spain or somewhere equally dry where water ingress into chimneys is unlikely.

We never seal closure plates fully and also make sure there is an airflow path outside the liner out of the pot. Permanent trickle ventilation through the entire stack.

As Phil says above, burn good seasoned wood and burn it hot and your liner will last well beyond its warranty. Liners absolutely do no need insulated to last a long time, they need to be installed properly with attention to detail. A good stove well installed with a good user will last longer than you think. Seal it up and introduce some moisture and it might not last til next Christmas..

An annual sweep by a qualified person is often a requirement of your household insurance.. so the advice from your sweep is good, he is making his annual sweep easier.

Detailing of the liner at the top of the stack is more important than anything else. We regularly replace other installers liners that have literally been thrown in through lack of care, knowledge, and often a safe working at heights setup. Record so far is a liner that lasted less than one year.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18050&Focus=304826#Comment_304826 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18050&Focus=304826#Comment_304826 Thu, 04 Jan 2024 21:38:34 +0000 Charli
That and insulating behind the log burner has made a world of difference to the room! Suspect the new more efficient log burner probably helped too.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18050&Focus=304830#Comment_304830 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18050&Focus=304830#Comment_304830 Fri, 05 Jan 2024 09:32:26 +0000 philedge