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Heat powered Wood Stove Fans

Posted by KingTurtle (My Page) on
Sat, Dec 10, 05 at 18:16

Has anyone seen these "eco" fans that sit on your wood stove and circulate warm air? They are advertised to improve heating efficiency by 35% by moving up to 300cfm of air. They run powered solely by the radiant heat generated by your stove using the "Stirling-cycle" powerplant mode.

The Stirling engine is something I've been fascinated with for awhile - an engine invented in the 19th century that runs basically by exploiting temperature differences to expand a volume of air to move a piston. It works on the same mechanical principle as the steam and internal combustion engines but without the energy expense. It exploits more subtle differences in temperature. It has been called the closest thing to a perpetual motion machine but of course it does require energy, just not alot, and often just the energy you lose anyway through loss.

On a wood stove, it takes heat from the stove and cool air from around the stove to move a piston which powers the fan and blows warm air from your wood stove. I'm curious whether it actually works and is worth the money. The prices I've seen range around $150 for a large fan.

Check out the website posted below. There are also specialty websites out there devoted just to the Stirling machine selling little models that will run based on the heat from your hand. Really neat. I've always thought it should be put to practical use.

Here is a link that might be useful: Radiant heat powered Fan


Follow-Up Postings:

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RE: Heat powered Wood Stove Fans

The Stirling and the Hydraulic Ram Pump are two of the best(cleanest) inventions of mankind. Thanks for the reminder, KT.


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RE: Heat powered Wood Stove Fans

Thanks for the heads up, KT!

Never heard of these, but would be ideal for me in Winter, as I live with solar electricity and heat with a wood stove....although with temperatures here now rising into the mid 30C (high 80F) and soon to hit the 100F+ mark, it's hard to imagine those crisp freezing Winter days (and nights!).

Found an interesting site with heaps more info about them (but still looking for an Australian distributor)

Regards,

Shax

Here is a link that might be useful: Sterling Engines


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RE: Heat powered Wood Stove Fans

I've been using the small fan (different brand) ever since it became commonly commercially available (10 years? maybe/probably longer). There is a larger one which I keep saying I'll buy but haven't yet done so. The amount of air moved is dependent on the amount of heat produced by the stove; 450 degrees (which is midline on my fireplace inset-stove) produces what appears to be near maximum airflow. Yes, it does work, and moves the heated air very well indeed. The small fan moves enough heat from source to keep a 15x27' LR, adjoining hall, direct-line 14x14 den, and indirect-line 14x20 kitchen more than comfortably warm, with warm air convection throughout the rest of the house even in windy 20-degree weather. I don't know if it's the difference in brand or "design improvements" in the past ten+ years, but mine is a smaller, neater, more minimalist design than one shown in KT's link. BTW, if you are looking for a strong "breeze" effect, the small style is not for you... the airflow is noticeable only for about 4' from the blades, which BTW, are pet- and child-safe.

Here is a link that might be useful: stovetop fans


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RE: Heat powered Wood Stove Fans

Thanks Meldy. Sounds like the small fan might work for me. My woodstove is in a room with an open loft so I lose warm air up (makes the bedroom very comfortable) but the adjoining living room with 8 foot ceiling is chilly.


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RE: Heat powered Wood Stove Fans

KT - To be honest, I bought it mostly as a joke, but the results have been seriously impresssive for such a little gadget. Several friends bought for themselves after seeing mine at work; one has a larger version and uses it to push the heat from LR fireplace downwards to heat the lower level of a split-level house.

If your heat is going upwards to a loft, why not use one of those reversible-direction ceiling fans to re-direct airflow downwards? The ones I've seen worked nicely both summer and winter, but the units did require electrical hook-up. Hmmm, gotta check the greenies to see if they have a solar-powered version....


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RE: Heat powered Wood Stove Fans

I have a ceiling fan and have used it, but it doesn't seem to help that much other than creating a draft that makes it feel colder. Will maybe try a combination of the two to see if I can get better circulation.


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RE: Heat powered Wood Stove Fans

I have one pointed at me right now from about six feet away, and while I don't feel much from it, I do think it helps. And I accidentally stuck my hand in it yesterday while feeding the stove, with no harm. But I've only had it a month, and I'm still considering how it works best.

I'm not sure you could call it a stirling engine though, because that's mechanical, and this works on some electrical basis, generating current from the temperature difference.

My one wish is that it did more about vertical distribution of warm air. Some friends of mine have one on the stove in their yurt. (Yes. They live in a yurt in the winter in coastal Mane. Hardcore.) The floor is always cold in there in winter, and the fan doesn't change that. The solution seems to be to get above the level of the stove for sleeping (3' tall loft bed does it), or stay moving to stir up the air in the place.

Dan


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RE: Heat powered Wood Stove Fans

Thanks Huisjen, I know what you mean. My floors are cold too but my BR is upstairs where the warm air rises. I need to do a better job of insulating the floor from the cold air.


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RE: Heat powered Wood Stove Fans

Oh yeah, cooold floors. My dream is to retro-fit radiant heat to improve floor temperature. We actually have a good set-up available with accessible floor rafters/joists/supporting beams, but I want the water pre-warmed by solar and DH isn't yet agreeing.

A yurt? In Maine? I sure hope they built it on top of strawbales! Gor, I'm cold thinking about the drafts they prolly have...


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