My brother has a wood burning stove which he says doesn't draw well in cold temperatures.
He wants to install a fan to blow air upwards via a "concentric" tube
This doesn't sound the right way to do it to me
What's the correct way to do this?
What we'd call an ID (induced draft) fan on a coal-fired power station. Sounds barking mad to me; ought to draw better in cold weather, for one thing.
Such things are available though and not that uncommon,power stations tend to have tall chimneys that stick well up above surrounding landscape. A dwelling might be in a small valley where a pocket of cold air forms.
G.Harman
It wouldn't draw better if its an uninsulated metal flu. Maybe they didn't do a good job on fitting it?
If it really needs a fan, putting it at the top of the chimney sucking seems to be more common:
accept that until ANY flue is warm you have a classic temperature inversion and flues dont draw well,.
It SHOULD get better as the flue gets full of hot gases. if it doesn't its a crap flue.
A rotating chimney cowl may help, see this site for that and other ideas:
Alan.
This is an ejector and they're not very efficient means of using the fan power, also there is risk of back pressure in the flue if there is a constriction above the ejector.
Induced draught fan is the way to go but it has to vent to atmosphere via an airtight pipe greater than 150mm and above the eaves.
AJH
It would be possible to T into the outside flue and mount a fan in (or indirectly off) the T. Alternatively, at the base of the T a small fire could be lit to encourage draw. If his flue isn't insulated, it might (probably does) need to be.
Agreed, never seen one before but that does seem to be designed for the job (even though I normally run a mile at anything with ECO in the name).
But WTF does this mean?
"Where wood burning boilers are located in an area where escape of combustion gases is deemed undesirable it is recommend to fit a Chimney Exhaust fan"
A chimney is normally a very safe, simple, and passive system. At the risk of stating the obvious, it likes to be in a pocket of cold air. Once you have warmed the air inside the chimney a bit, its expansion generates a pressure differential which draws fresh air into the combustion chamber. Also, by having reduced pressure within the chimney, this should ensure that flue gases which potentially contain carbon monoxide and carcinogens don't escape into the house but get ejected above the roof. If you aren't getting a draught (sorry for earlier typo) with a warm chimney, it is probably partially blocked, as GH suggests.
Yes, if its just being lit for an hour on occasional days in the evenings to look nice then maybe the chimney hasnt warmed up,
The chimney may even be damp.
Or is it lit all day every day?
[g]
My chimney draws immediately from cold - even the smoke from the firelighter goes straight up. That's with a stove, 5" liner, 7m long.
Once it's hot the draw is incredibly powerful. Still going to pick up a CO alarm today though, something I really should have done already ;->
As an owner of a wood burning stove and a chimney that I have had trouble with, I am recognising all the possibilities that Harry is suggesting.
The OP needs to find a local chimney specialist rather than try to solve this the DIY way.
As most of the contributors to this thread have said a flue without problems draws immediately.
The OP sadly fails to give us enough information to go on and do a reasonable enough analysis of the cause. For instance, I do know with my system that if the air is cold and static and I'm doing a re-light with paper and sticks, that throwing in some additional loosely rumpled newspaper as well will get the air in the flu moving.
Rob
If you look at the OP, the giveaway bit is "My brother..."
nothing sad about it, I know about as much about your setup as his
Possibly the chimney is cooling the flue gases excessively, which suggests it's a chimney design fault, e.g. 1/2 brick thick with 3 sides exposed or some such.
Warm air rises, and there isn't much you can do to stop it other than cooling the warm air or having no cool air replacing it at the bottom. The usual draw test for a flue involves warming it for 5 or 10 minutes with a camping gas stove or similar.
We have a large open fire (used primarily for cosmetic purposes), on which we have only ever burnt wood, and I agree with you both. In particular, I would emphasise Harry's first point; if the chimney is to draw well, air has to be able to get into the room to replace that which rises up the chimney. In modern houses with well sealed windows and doors, this is often lacking. If we don't have the trickle vents over the windows open, and the door open into the hall, the fire will smoke into the room. It is particularly important when the fire is first lit, before the structure gets warm, as that is when the draw is least.
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