Chimneys.. again.

[Tim Lamb]

I am approaching the end of the *getting ready for the log burner* saga and would appreciate views on ventilating the top of the chimney.

I have installed a 7" double S/S liner, insulated with pre-formed rockwool sleeves which leaves a fair bit of air space in a red, single brick Victorian chimney. The chimney top is closed off with a S/S plate I made to run rainwater off to the edge of the brickwork.

I still have scaffolding in place and could easily core drill through to the old flue.

Would there be any benefit and if so what to use as an insect barrier. My cores are 50mm and 78mm.

regards

[jim]

from doing what?

jim

[mike]

Ventilating the airspace that is now enclosed between the original brick stack and the new liner, presumably.

[Jules]

Hmm, surely a wood stove needs to draw air for the fire from somewhere - can't the chimney airspace be used for that (as presumably it'll gain a bit of pre-heat from the exhaust going up within the liner)?

[matthew.larkin]

Jules et Jim aident - ca m'amuse!

[Jim]

I've never seen a solid fuel stove that doesn't just draw air in from the room. Although you can get a fireplace which takes air in from under the floor - the Baxi Burnall. We used to have one in a previous house, it worked excellently.

It's quite common on the continent to install ducts through the air space in the chimney and blow heated fresh air round the house as a form of central heating.

[jim]

pourquoi?

[Tim Lamb]

Yes. First paragraph:-)

According to my *Collins complete DIY* I think the answer is yes.

I see Screwfix do a plastic 70mm soffit vent but my core drill is 78mm.

For anything over 4.9kW you have to have an air vent so I have put a duct through the hearth and fitted an extra under floor airbrick. My particular log burner comes with a ducted air option.

regards

[jim]

are we assuming the chimney was airtight in the first place? personally I wouldn't bother - what would it prevent? some heat from the liner will keep it warmer and dryer (relatively) anyway - venting it would add what?

cheers jim

[mogga]

I'm pretty certain they tipped a ton of insulation stuff down between our liner and the chimney...

[mogga]

insulate. That way the crud stays hot until the top and leaves?

[jim]

passim)

[Jim]

May I ask what manufacturer?

[Martin Bonner]

That's the other way of doing it. Double liner then tip insulation in.

The OP has "double liner insulated with pre-formed rockwool sleeves"

Personally, I think I'd tip more insulation down - improve the draw.

[jim]

how's that work then? jim

[Tim Lamb]

Clearview 650.

10 or so weeks delivery:-(

regards

[Tim Lamb]

Hmm... Vermiculite bonded with cement seems a bit permanent to me. With a struggle I can get my flue out again.

I'm going to stick a couple of vents in anyway. Nobody has suggested any likely problems.

I think the draw is ample as you can warm your hands in the flow of centrally heated air!

regards

[andrew]

It's not, it has the consistency of of a puffed rice cake when I've mixed it (using high alumina cement that's good for 700C) but I cannot remember the mix, probably about 10:1.

AJH

[Tim Lamb]

Yes, but you wouldn't be able to pull a 6.5m long flue out again. I hope I never need to but things have been evolving here since Victoria.

Also, S/S liners do not come with any sort of life warranty.

BTW. I have had a digital survey done of the old barn and taken out the concrete floor. The next problem is to get a steel frame designed without creating unaffordable architects/structural engineers fees:-(

regards

[jim]

why use cement? where's it all going to go? ours are just loose vermiculite - when time comes to change the liner - get a large dumpy bag, open the soot door and stand well back!

what will your vents add to the sitiuation - seems like extra wasted effort and expense to me...

Anyhow enjoy!

Jim