Help understanding air draw and venting?

[brickie in oz]

Re: Help understanding air draw and venting?

Im doing a small job for some friends 20kms from home up in the hills and thays all hilbillies up in them thar hills.....

We looked at buying a block of land up there last year with creek frontage, I was going to sit and watch the creek drikin moonshine and playin the banjo.. but my wife didnt like the idea.

[Amac]

Re: Help understanding air draw and venting?

If you want serious draw over a long chimney, you insulate it to ensure the gas doesn't cool and contract, losing velocity as it travels up the stack. If you can't insulate it, you taper it, so that as the gas contracts from cooling, the velocity is maintained.

Great contribution wotavidone - I wondered what the insulation was for - that explains a lot.

[GianniFocaccia]

Re: Help understanding air draw and venting?

Wotavidone,

The trek to the top via stairs sounds like quite an adventure. Any pics you could share from the outside?

[Amac]

Re: Help understanding air draw and venting?

It's a hollow concrete shell, which supports a flue made of special firebricks.

I'd like to see the "indispensible tool" they used to build that one.

You don't want to suffer claustrophobia or vertigo in that job. Well base jumpimg is not on my list of 100 things to do before I die - but maybe I should add it in as the 101st (and most likely last)

[cobblerdave]

Re: Help understanding air draw and venting?

Gudday
Most old brick chimneys taper in over the fireplace then expand out over this point to let the smoke expand out and of course suck more smoke in. At the top they again use this method of tapering the end by using a chimney pot to again restrict the smoke and then let it escape into the open air again sucking the smoke behind it.
Used to live in a house with a fire box and single skinned metal flue that exited the wall, behind it. Worst still it was on a southern wall. Try to lite that from cold on a chilly night was interesting. What would happen was the smoke would only get so far up the flue due to it being so cold and of course the fire couldn't breath and the room started to get smokey. If you were really unlucky and the condesation in the cold flue had built up suddenly the smoke would disturb it and you got a stream of black water down the flue that would put you fire out for good. We did't own the house so it was never fixed with a double skinned one ...we just kept a log in it at all times.
Was going to fit a metal chimney to the WFO but decieded to build the widest chimney in brick, have plenty of bushes to cut the wind so I could keep it really low...no soot stains... works for me


Regards Dave