Fan for Wood Burner

[Basil]

Just been having a little google around for these.
Prices seem to be between £45 - £120.  That's a hell of a price range!
OK, avoiding the cheapies, obv, what should I be looking for?
Anyone any experience, observations?

[ferret]

all I know is ......... they do make a difference but, bloody expensive for what they are, a friend of mine has a few windmills from the beach in her fire place they sort of work but then again she is a bit strange (but in a nice way). Some of the proper ones just work on the rising heat others are made with metal that reacts to heat but I've been looking around for a fan like object made of light weight metal that will turn very easily something I can molish in the shed
anyway this is my only experience of them sounds quite similar to yours Basil   

[Kim]

It's a peltier cooler running in reverse, a couple of heatsinks and a CPU fan, right?

Unless someone's actually bothering to make stirling engines for them?  That would be cool.

Windmills from the beach clearly won't do anything other than spin around in the rising air and look pretty.  The objective is to force the air to flow in a direction it doesn't want to do naturally (ie. out, rather than upwards), and to achieve that with a fan requires power.

TBH, you could just get a convenient computer case fan (or two) and run it off a random wall-wart from the spares box.  Putting the heat where you want it is going to be well worth the piddling amount of electricity involved.

[Basil]

That would be cool.  Charge your phone from your log burner.

[Kim]

That would be cool.  Charge your phone from your log burner.

Easily done with a peltier and some electrickery to sort the voltage out, I expect.  There's a woodburning camp stove (discussed in one of the relevant threads) that does just that.  I keep failing to get round to molishing one.

[Basil]

Good points Kim.  The cheaper ones look like they are simply pretty windmills.
Hmm.  This is going to cost.  Bugger.

[ferret]

here you go, this one even has pistons you can watch go up and down

http://www.orionheating.co.uk/accessories/stove-fans/

[Kim]

Good points Kim.  The cheaper ones look like they are simply pretty windmills.
Hmm.  This is going to cost.  Bugger.

Most of the ones I've seen look consistent with a peltier design:  A bit of metal in contact with the stove gets hot; another bit of metal shaped into fins to dissipate heat to the air; peltier sandwiched between the two to generate current from the temperature differential; and a fan powered by the peltier blowing air through the fins and into the room.  Simples.

[Kim]

here you go, this one even has pistons you can watch go up and down

http://www.orionheating.co.uk/accessories/stove-fans/

Stirling engine.  Now that's a thing of beauty.

[Basil]

*Checks pennies.*

[mrcharly-YHT]

Good points Kim.  The cheaper ones look like they are simply pretty windmills.
Hmm.  This is going to cost.  Bugger.

Most of the ones I've seen look consistent with a peltier design:  A bit of metal in contact with the stove gets hot; another bit of metal shaped into fins to dissipate heat to the air; peltier sandwiched between the two to generate current from the temperature differential; and a fan powered by the peltier blowing air through the fins and into the room.  Simples.

They are a bit more than just that. The base is also a clever bi-metalic bit that bends and lifts the peltier away if it is getting too hot.

[Diver300]

We've got one of the Peltier* ones, and my sister-in-law has one of the Sterling cycle ones. The Sterling cycle one doesn't self start, and needs to be flicked in the right direction once warm. The fan rotates slowly, and is metal to be heavy enough to act as a flywheel.

The Sterling one got dropped and stopped. Inside the big cylinder is a displacer that is held together with friction. Pushing it back together got it working. The materials are interesting. Aluminium displacer, full of holes and spirals of brass wire to be a regenerator. The piston is graphite running in a glass cylinder.

* The Peltier fans do not use the Peltier effect. They use the Seebeck effect, AKA thermoelectric effect. However, Peltier cells are made in quantity for coolboxes and the like, and can just as well be run in reverse to generate electricity from a heat difference rather than the other way round.

[Tewdric]

I'm not sure about these things given that the point of wood burners is the bone-penetrating radiant heat they give out.

[mrcharly-YHT]

I'm not sure about these things given that the point of wood burners is the bone-penetrating radiant heat they give out.

If you have a woodburner in a large room, the heat is concentrated around the woodburner. The fan circulates the warm air.

They are very popular on narrowboats, where the air doesn't circulate well and parts of the boat can be a considerable distance from the stove.

[contango]

Friends of mine in the US has a hunting camp which is essentially a single long room with a wood burning stove at one end. They've got a fan that powers itself from the heat generated in the stove.

Not only does it give you a very visible cue that you've got the fire nice and hot but the amount of heat it shifts into the room is remarkable. Until it starts turning it's very warm if you're within a couple of feet of the stove but stays cold further back. Once the fan starts spinning it really does shift the heat.

A UK friend has one in his house, to make sure there's heat available for his disabled wife and she doesn't have to be getting up to turn the fan on and off.