Chimney Insulation

[garob]

Can anyone advise me as to what to use at the bottom of my chimney to act as insulation around the stainless steel flue and to stop heat from my log burner travelling upwards ?
I have a heat proof board but I wanted to wrap something around my flue, is this a good idea ?
Thanks for any help.
Gareth

 

[Penners]

A widely used technique is to fill the void between the flue and the chimney walls with vermiculite granules. Insulating the flue in this way isn't so much to prevent your heat from travelling upwards (that will happen whatever you do) but to ensure that the flue gases don't cool too much on their way up and deposit corrosive acids on the flue interior.

Insulation of the flue should be done, even if you've used a pre-insulated double-wall flue.

There are also flue insulation sleeves that you can buy.

 

[MdB]

Leca is also an alternative to vermiculite which is sometimes used. I've no idea as to the pros / cons of the two though.

 

[Penners]

I don't imagine there's much difference in performance (that's not an informed opinion - just a guess).

Other considerations? Well, vermiculite will compress if it gets wet (shouldn't be a problem if it's properly installed in a capped chimney), whereas Leca won't. But Leca is something like twice the price of vermiculite (by volume).

 

[MdB]

Leca is around £70/m^3. What is the bulk price of vermiculite?

I would guess vermiculite is probably a better insulator than leca but I could be completely wrong.

 

[Jon Maine]

Leca is heavier approx 500% than vermiculite and maybe not such a good insulator could be a little to much weight for the register plate to carry.

Vermiculite is around £10 a 100l sack plus vat so maybe more expensive than leca but easier to handle.

We just lined the two main ground floor flues here and one 2nd floor and got through 56 100l sacks!

Drop it in from the top, mix the first bag or two with some lime or cement with enough water to coat all the granules, drop this down from the top which forms a crust on top of the register plate which stops the vermiculite dust falling out for ever and a day.

As Penners says stops caustic stuff condensing in the flue too.

 

[Penners]

Leca is around £70/m^3. What is the bulk price of vermiculite?

I was obviously looking at the wrong websites. The leca I saw was supplied in 100l bags at - if I remember correctly - about £19 a bag. Vermiculite was, as Jon says, £10 a bag.

 

[Schoolmarm]

How do people replace the liner with all that stuff?

 

[Jon Maine]

Well the theory goes that it will make the liner last much longer. As for when the inevitable does occur, it will essentially in theory all be reusable ( even the cast stuff could be broken up and used in the loose infill) but would have to be drained out the bottom, collected and with the new liner in place poured back in. Sounds like a messy job that would have to be thought through to avoid problems. Our largest one holds 2.75 cubic metres, so a lot of buckets or bags required!!

 

[MdB]

Leca is around £70/m^3. What is the bulk price of vermiculite?

I was obviously looking at the wrong websites. The leca I saw was supplied in 100l bags at - if I remember correctly - about £19 a bag. Vermiculite was, as Jon says, £10 a bag.

http://www.mikewye.co.uk/naturalproducts.htm#leca
With a 10% discount (which they give most people who ask nicely) it works out at £70/m^3 = £70/1000l.

Vermiculite is probably better for this application though (a completely uninformed guess).

 

[Jon Maine]

http://www.mikewye.co.uk/naturalproducts.htm#leca
With a 10% discount (which they give most people who ask nicely) it works out at £70/m^3 = £70/1000l.

Vermiculite is probably better for this application though (a completely uninformed guess).

I just checked that out Mike Wye link, it works out £160 per cubic metre in 50kg bags or around £70 a cube in bulk bags but seems he wants to sell you either a full load or charges you a pallet rate for delivery.

 

[MdB]

Just looked this up as I will have two chimneys to fill at some stage in the future.

Leca - 0.1 to 0.15 W/mK
Vermiculite - 0.06 to 0.07 W/mK

so Vermiculite it roughly twice as good as Leca from a insulation point of view.

 

[Jon Maine]

Yes and in a chimney it does not require the strength of leca and certainly benefits from the lightness of vermiculite, just go steady pouring it in if it is windy :shock: it took us about 5 hours to fill 3 flues with 56 bags 10 metres up a scaffold with 3 people on it so is a fairly quick job.

 

[Penners]

When our chimney was filled with vermiculite by the HETAS folk who fitted our woodburner, they sealed up an inspection plate just above fireplace level. I asked them why they'd done this, and the guy replied "because there's enough vermiculite up that chimney to fill your sitting room up to knee level"! :shock:

 

[Jon Maine]

When our chimney was filled with vermiculite by the HETAS folk who fitted our woodburner, they sealed up an inspection plate just above fireplace level. I asked them why they'd done this, and the guy replied "because there's enough vermiculite up that chimney to fill your sitting room up to knee level"! :shock:

My you have a big one :shock: :shock:

 

[Schoolmarm]

snigger

 

[Penners]

When our chimney was filled with vermiculite by the HETAS folk who fitted our woodburner, they sealed up an inspection plate just above fireplace level. I asked them why they'd done this, and the guy replied "because there's enough vermiculite up that chimney to fill your sitting room up to knee level"! :shock:

My you have a big one :shock: :shock:

I suspect he may have been exaggerating a bit - but we men tend to do that, don't we?