It strikes me that if we could extract more heat from the flue and attach a fan like one you'd see on a fan assisted boiler, we get even better heat output where its wanted and not up the chimeny. Ive not seen anything on the market that does this...so do you think it'd be worth experimenting with?
Steve
Why not just wrap a copper tube around it and feed a small rad with a small fan to keep the ambient temp up
A pretty good trick on a 90% efficient boiler!
Don't forget the tars which will condense out of the flue gases and stick to the liner until such time as they ignite. Burning wood often results in chimney fires
In message , RW writes
When first married, we lived in a caravan fitted with a small solid fuel stove.
The flue passed through a tall galvanized water tank. I can't report on the performance as we used the farmhouse facilities and didn't need hot water.
regards
Our little (10') caravan in Wales has a gas fire and we often sit the kettle on it to heat water.
Waste not ...
Mary
I hope you don't drive there in your "large car" ?
DG
Don't forget the tars which will condense out of the flue gases and stick to the liner until such time as they ignite. Burning wood often results in chimney fires
At what temperature is the tar likely to condense? If you could sense the flue temp in various stages up the flue, i suppose you could prevent the flue from getting too cold?
I was thinking of using something like a sleeve over the flue with a fan blowing air down the void between the flue and the sleeve and let it exit at the log burner. if you used a series of sensors attached to the flue controlling the fan speed dependant of flue temperature you could prevent the flue from getting too cold that there would be insufficient draft so the fire would burn ok and there would be limited condensing of tars.
Steve
A must have for every Drivel
This pre supposes that the flue temperature is high enough to extract more heat without the actual exit temperature at the chimney pot falling below the dew point of the flue gases. In general wood burners need a rather high flue exit temperature, typically 150C+.
Fans are a different matter, in a gas condensing boiler they're probably necessary to eject the exhaust, because there is little chimney effect ( short balanced flues being typical) and the flue gas is deliberately cooled below the dewpoint (because the condensate is clean) so there's little added buoyancy to move the gas . This is not so with a woodburner because, from the above, the flue is both hot and the chimney tall ( legal requirement to vent above eaves). Condensate, should it occur, is likely not very clean either.
Having said that fanned stoves do have the ability to burn far more efficiently. Woodchip burners and pellet stoves do have id fans as you suggest, they also have far more surface area on the heat exchangers than a typical woodstove.
The only decent logburner with a fan that I have experience of is a very expensive down draught device that has a forced air primary inlet which essentially blasts the wood gas into a secondary combustion zone and simultaneously induces secondary air, the resulting high temperature and turbulence result in a very clean burn.
AJH
sure, but one of the attractions of a woodburner is that it doesn't need electricity.
The adverts state SPECIFICALLY that the fans don't need batteries or electricity but are powered by the heat of the stove.
Yes it looks like they're powered by a Thermo Electric Generator, similar stove top designs are made in Pakistan based on a stirling engine.
AJH
Those fans look like they simply stir the air around the boiler, They do not work in the flue at all. I think they should be quietly filed under 'Greenbollocks' along with solar volatics on the roof, windmills on te roof, CFL lightbulbs...
I cannot envisage the equivalent of a turbocharger working well in a stove environment at all. Mind you, with a proper pulverside load of coke hops. you could make a solid fueled gas turbine to generate electricity AND et. Now theres a thought. The noise would be impossible tho.
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember The Natural Philosopher saying something like:
They do actually work in a small space, like a narrowboat cabin. Be utterly useless in a larger room, iwt.
I may be "teaching grandmother to suck eggs" but it is very important to ensure the wood is thoroughly dry to get the best effeciency. Store it for at least a year in a well ventilated dry place before use.
M.
Or you can store it for couple of months next to the stove, or for about
5 minutes IN the stove.That gets the moisture out all right.
I've often burnt relatively freshly cut wood. It burns. It takes a hotter fire to dry it, thats all.
I tend not to use 'wood burning stove' and 'efficiency' in the same sentence anyway.
It does burn but, since some of the energy is wasted boiling water which goes up the chimney, then it could be seen as less efficient.
However the reason I do not like burning "green" wood is the smoke produced is much more unpleasant.
Many would argue that it's better for the environment as it's not using fossil fuels.
M.
Well it is using fuel that will be fossil one day if left longn enough ;-)
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