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I'm considering a stove fan to distribute heat from a small wood burner. The prices of commercial Peltier-type stove fans seem to range from £25 to £100.

Is there likely to be a significant difference between them in efficiency, or is this just marketing hype. If there are functional differences, what should I be looking for in the specifications?

Notes: I'm UK based, should that be relevant for supplier and pricing answers. I'm aware these can be made DIY but that's not what I'm asking here. I'm also aware of Stirling Engine versions (starting ~£150) but that's probably off-budget unless there's a really good reason I should buy one of those instead.

  • Is the "small wood burner" a wood heater or a wood stove? Perhaps more importantly, is it solely used for heating or is it used for heating and cooking? Can you specify it's make/model? – Tim Mar 3 '18 at 5:57
  • It's a small (5kw) room-heater, a Smellie Crator (unfortunate name of the week) if that helps. (www.whatstove.co.uk/james-smellie-crator-stove-reviews) – Cheeseminer Mar 6 '18 at 18:43
  • Great name! Nice, flat top. If you end up getting a thermoelectric stove fan, positioning it in a back corner, and having it blow diagonally across the stove-top, will probably add another 4-6 months to the life of the product. – Tim Mar 7 '18 at 15:13
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Given that the 'efficiency' of Peltier/Seebeck/thermoelectric systems is very, very bad — even under ideal conditions — if one manufacturer comes up with a low-efficiency design, you are effectively comparing very, very bad with very, very, very bad.

If you want one of these things because they just look cool, then fine. If you want to use it to impress your friends, then fine. If you want to use it as an educational tool, then fine. If you are off-grid and have zero access to electricity, then fine. Otherwise, if you just want to mix the air in your room efficiently and inexpensively, consider the following:

A 'large' 12V computer fan (e.g. the 200mm NF-A20 FLX from Noctua) can draw less than 1W when running at maximum speed (actually 0.96W @ 800RPM). All 3-pin fans can run at lower speeds (and be much quieter) by simply dropping the voltage. A Low Noise Adapter is included with each of the above fans, does just that, and drops RPM down to 550 and power draw to 0.66W. At that speed it's virtually silent and circulates 100.8m³ per hour — which I suspect would be more than sufficient to meet your needs.

If your search showed thermoelectric stove fans ranging between £25 and £100, then the middle of that range would be £62.50. Given that a NF-A20 costs £27 from Amazon.uk with free delivery, you'd have £35.50 left over if you bought one of those instead. If you are paying 15p/kWh, then £35.50 would pay for 236.667kWh of electricity. It would take the NF-A20 about (236667/0.66=) 355,000 hours / 14,791 days / 40.5 years of continuous use to consume 236.667kWh of electricity.

The Mean Time Between Failure of the NF-A20 is 150,000 hours / 6,250 days / 17.1 years of continuous use and Noctua backs that up with a 6-year warranty. By contrast, most thermoelectric stove fans have warranties of only a year and die around then. Some of the better ones have 2 year warranties. I haven't personally seen any with a 3 year (or longer) warranty. I doubt that any have a 6 year warranty. Most of the ones I've read about lasted between 1 and 2 years before failing.

So:

  • thermoelectric stove fans on a seasonal duty cycle last ~2 years
  • computer fans on continuous cycle can last ~17 years
  • the money you save buying the latter can power it for ~40 years

A little bit of easy math shows that thermoelectric stove fans don't make financial sense if you have access to electricity and mixing air efficiently and inexpensively is what you are actually trying to accomplish.

Computer fans are not the only way to mix air, of course. Even a regular ceiling fan would probably end up cheaper (and be more effective) in the long run. You can also do the same thing with some copper/aluminium pipe and a pipe bender — although that is definitely a different aesthetic. There are lots of choices (none of which exploit the thermoelectric effect, and some of which are completely passive).

Before spending money on a thermoelectric stove fan of any kind, I'd encourage you to look into the other options.

In essence, thermoelectric stove fans are primarily an expensive gimmick/toy. It makes virtually no sense for the vast majority of the population to buy one.

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    Thanks for the answer Tim. It's an interesting and informative take on the problem and it's always good to look at different routes to the end aim. The issue I have with the 'computer fan' approach is primarily that such a fan would need a dedicated power supply (adding to the purchase and energy cost) and that the vicinity of log burners is not a trivial place to run wiring etc. (Also I don't have a socket handy). So while I like the approach, I'm not sure it's a workable solution for me. – Cheeseminer Mar 2 '18 at 14:01
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    12V DC fans are trivially-simple devices to power. You don't need an actual computer PSU to power one. You can use a 5V USB charger (which would run the fan at 5/12= 42% of max speed), or you can use a 6V lantern battery (for 6/12= 50%), or a random combination of rechargeable AA/C/D-cells, or a lot of old mobile phone chargers, or any (variable) AC/DC power adaptor, of which there are squillions on Amazon.uk for under £10 a pop. At most, these approaches drop efficiency by ~20% which won't make a dent on the 800%+ lead that they have over thermoelectric. – Tim Mar 3 '18 at 5:34
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    As far as mounting is concerned, the reason thermoelectric oven fans fail quickly is because they sit directly on top of the oven. If you want electronics to last, you don't mount them in a hot place. Better to mount a fan on a wall behind or next to the oven, and have it blow air from there. Works just as well, no wires on the floor, and the electronics don't fry due to the heat. You might even have power on the other side of that wall you could tap into. – Tim Mar 3 '18 at 5:40

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