Wood stove: Insulating above the closure plate, is it common? Good idea?

[Krome10]

Hi all

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

 

[Spectric]

A type of mineral wool is used to insulate the space between the inner flue and outer sleeve on twin wall pipe so in that situation it is non combustable but cannot say if it was loose with plenty of air around it, if it would remain so. Considering the amount of heat given off by a woodburner I would not worry about a little loss, it will warm your chimney stack and keep any damp at bay plus put warmth into the rest of the building.

 

[eribaMotters]

I'm trying to visualise what you are saying. I thought the chimney void around the flexible liner was filled with vermiculite that was poured in from the top when the liner was fitted.

Colin

 

[Sachakins]

Wouldn't worry about it, once the void is heated, the hot air will fill space and heat down from the plate, at this point the excess heat will come out below into the room anyway.

 

[Krome10]

Many thanks for the replies

The void wasn't filled with anything. Not sure why. Can't remember if it just wasn't discussed at the time or whether the fitter had reasons not to. I know access to the top of the opening in the loft is restricted, so that might have been a reason. Anyhow, it is what it is I guess, and I've no intention of adding it retrospectively as I'd have to undo much of the fitter's work.

Thinking about it though, from what I remember the space around the flexi flue liner is not all that much at all. It's a narrow space. Perhaps that's why vermiculite wasn't used? Not sure...

once the void is heated, the hot air will fill space and heat down from the plate

I never thought of it like this, but it does make sense. Is it along the same lines of the "heat moves to cold spaces" theory? So, because the flexible flue liner will be letting off loads of heat into the chimney void, it's already pretty toasty in there. So the hot air that hits the underside of the closure plate is more likely to make it's way back into the relatively cooler room. Just thinking aloud; might have completely misunderstood you!

I'm trying to visualise what you are saying.

Sorry, my explanation wasn't all that clear. It's a basic builders opening, but where the lintel sits lower than the closure plate. So like this.

Many thanks

 

[Sachakins]

Many thanks for

I never thought of it like this, but it does make sense. Is it along the same lines of the "heat moves to cold spaces" theory? So, because the flexible flue liner will be letting off loads of heat into the chimney void, it's already pretty toasty in there. So the hot air that hits the underside of the closure plate is more likely to make it's way back into the relatively cooler room. Just thinking aloud; might have completely misunderstood you!

Yep, that's exactly what I meant

 

[mccpe]

Insulating the chimney void is a good idea. Plenty of info on why if you Google for it. I have insulated three flues, two with micafil (vermiculite grains) which is easy if you have access to the top of the chimney to pour it in, and one with rock wool. If you want to be extra sure that the insulation is fire proof, you can buy rock wool type insulation specifically for wrapping a flue liner.

 

[Jones]

Insulating with vermiculite or expanded clay round flexible liners will keep the flue gas temperature up and give a better draw. With lots of clay and concrete liners it's part of the system . I would definitely add something, even stuffing some rockwool up from underneath should help.

 

[Agent_zed]

if you have a flat stove top stick a stove fan on it and it will help move the air from in the void and generally help spread the heat into the room. They can be picked up for about £15-20 these days.

 

[Majimoto]

The only problem with vermiculite type materials is when anyone has to go back in for repairs or suchlike.
All those little pearls will escape everywhere.

That is why I only use fire retardant insulation rock wool type.

FWIW.

 

[HamsterJam]

We had a new log burner fitted at a previous property.
We uncovered a catalogue of issues with the previous installation (which is another story) but ended up with a system similar to what you describe.
Our installer filled the chimney and void above the closure plate with insulation granules. The issue we had afterwards was he hadn’t fully sealed the closure plate along the back edge so we were always vacuuming up a few escaped granules which I think dropped out as the plate expanded and contracted.
A bead of high temp adhesive solved that.

 

[Ollie78]

Mine is just a steel plate, no insulation. Exactly like the above drawing. The pipe is sealed into the plate with a sort of clamp that joins to the flexible liner and some fire cement.

+1 for stove top fans, makes a real difference.

Ollie

 

[Cabinetman]

I came across vermiculite when a new stove was being fitted, about three 1 ton builders bags full cascading down into the room! The stove fitter said it has gone out of use mainly nowadays.
Ian