interesting article on external air stoves

[sm_jamieson]

In relation to the recent threads about wood burning stoves, etc. this article may interest some:

Simon.

[Huge]

The author is welcome to come and sit in the howling gale under the sitting room door caused by our fireplace. I'd give my eye teeth for a room sealed woodburner, but the building regs mean we'd have to rip out out our rather nice Cotswold stone fireplace to fit one.

[The Natural Philosopher]

"How to set up straw men and demolish them in three easy steps'

The point is to have enough air to FEED THE FFF*NG FIRE. which is the one thing they failed to mention.

IF there isn't, the house eventually goes to negative pressure and the smoke wont go up the chimney and there is no draught to feed the fire at all.

The reason for having vents close TO the fire is so that you dont get foot level draughts of cold air rushing towards it from somewhere else...

[The Natural Philosopher]

+1. See my earlier posts.

The way I fixed it in our bedroom was a pipe from the register plate up into the (ventilated) attic.

Downstairs the open fires are fed by underfloor vents drawing air from the (ventilated) cavity under the floor..

[polygonum]

The other point is to avoid outside air being pulled into the house and up the flue when there isn't a fire!

[harryagain]

It is a load of bollix. The air supply regulations demand in the UK is the one described on the site as "passive." So if you follow the advice on this site you block that up?????

The problem this stupid git has failed to identify is that the chimney shown is too low, ie not projecting above the ridge height. Hence wind can cause negative pressure at the top of the chimney.

He is also assuming houses are "draughty." enough to let combustion air in.

[Tim Lamb]

In message , sm_jamieson writes

Hmm.. Seemed more or less plausible bollocks to me.

Using the negative air pressure caused by high volume extraction to veto direct air supply while advocating room sourced combustion smacks of

1984 double think!

[Capitol]

Not a problem with a flue damper.

[sm_jamieson]

My open fires have venting under the grate, but the air will take the easiest path, and there is nothing to make it take air from underfloor supply. If the grate is not cleared and ash clogs it up then air will be taken from the room. Also, the Burnall fires have a air valve which if shut will not damp the fire very effectively since it can just take air from the room instead. That is, unless the air flow and pressure dynamics make air drawn through the fire from below extremely favourable relative to air from the room. I know they say coal fires burn best with the draught from below whereas wood burns best with air supply from above, thus the different air intakes on a multi fuel stove. There maybe some type of impedance mismatch situation about taking air from the room rather than a nearby external vent, but I'm sure this would reduce as the room size increases. My physics is probably not up to it though. Simon.

[Colin Stamp]

I've always been quite impressed with the amount of difference the butterfly valve on my Burnall clone makes. The thing sucks plenty of air under the lounge door too, but a significant amount definitely comes through the air pipe.

Cheers,

Colin.

[Dave Liquorice]

It used to on ours as well. The previous owners had said "if you use the fire it'll burn a lot of wood/coal", I investigated, no butterfly, fitted one and replaced the lace ash box. It would still burn fairly well fully shut but open up and you had a mini forge hearth. B-)

Too many other drafts to notice where they came from. Under certain conditions, wind direction internal/external doors open/closed in a particular way the draft through that vent would reverse and fill the outside, at ground level, with smoke. B-)

The external air vent for the burnall was retained and brought up to the new slate hearth underneath the stove to provide ventilation in a room that would only have a single door for ventilation, window DG'd and no trickle vent. Stove is rated at 10 kW with 7" flue so has a need for a good air supply.

[Harry Bloomfield]

Spot on! I lived through the days of coal fires in my youth, which were vented by the room. The only place which was ever warm was right in front of the fire and there was always a cold draught on your back, due to the air pull of the fire. Similarly with gas fires burning the room air. Neither can effectively warm a room, drawing combustion air from the same room.

[sm_jamieson]

is article may interest some:

asiest path, and there is nothing to make it take air from underfloor suppl y. If the grate is not cleared and ash clogs it up then air will be taken f rom the room.

e fire very effectively since it can just take air from the room instead.

gh the fire from below extremely favourable relative to air from the room.

s wood burns best with air supply from above, thus the different air intake s on a multi fuel stove.

from the room rather than a nearby external vent, but I'm sure this would r educe as the room size increases. My physics is probably not up to it thoug h.

Maybe my underfloor air is lacking then. The house has three air bricks at the front and 2 at the back ducted under a solid floor to outside. It feels breezy down there when the floor is up. I am happy with the burn rate etc. but the valve does not seem to make much difference so maybe it is not dra wing much from underneath, which I am not so happy with. If I add airbricks, the floor may lose more heat unless I insulate between the joists. Hmm. Simon.

[Tim Lamb]

In message , sm_jamieson writes

Perhaps the seals around the ash tray/doors are leaking?

If I fully close the ducted under floor supply to my Clearview, the glass doors soot up!

On the Cotswold Stone fireplace, I wonder if a bit of precision boring work with diamond core drills and extensions could create a duct without other damage?