My brother has used one for years - I was asking him about it just the other week and he's convinced it's really effective. I think his is NZ-made, but those made o/s are certainly way cheaper.

I have no experience with fire fans, but I used to have a freestanding fireplace. It produced a massive amount of heat that all went straight up and didn't move between rooms. Because of the hole around the chimney I reckon quite a bit was lost as well.

I would expect any fan that pushes air down or even out to be very effective. I wonder if a heat transfer kit even within the same room would work - if it had a strong enough motor to push the air down it could do.

@timmmay: some of the key advantages of these fans are that they're cheap to buy, no installation is required, and they don't need power. Simply plonk on the fire and let convection do its thing. This is the type of one I'm talking about, but the OP may like to clarify if I've got the wrong end of the stick.

https://themarket.com/nz/p/fireplace-fan-heat-powered/4969-AAQEAN700?skuid=6613731

That's pretty clever. There are larger versions available on The Market which would probably work better. The small one says 100CFM which is a heck of a lot of a passive fan.

Parents-in-law have one. 

Makes a difference and is 'free' and silent.

Maybe not as much as you'd think - if your lounge was huge, maybe not, but for a smaller room - yep.

If the fan isn't powerful enough to blow the warm air across the room before it rises, it won't make any real difference at ground level where you're sitting. But if you could reverse the convection direction, so that warm air goes more-or-less across the floor to you, then up due to pressure from the fan, then cools and goes down at the fireplace, it would be a huge win.

The example web site linked says "and the fan will conduct heat from your stove" (my emphasis), so perhaps it's some kind of Stirling engine or Peltier device? We need someone to take one apart to see how it works!

However, if the fan is powered by convection, I'm not sure there would be much energy that could be extracted from the fairly slow vertical convection motion of the air to be converted to rotational motion of the fan then to quite fast lateral movement of the air. Unless there's a large slow energy extraction "windmill" geared to a small air blowing "fan", I suspect you would get the same amount of benefit from an angled airfoil-shaped piece of cardboard. 

It's not convection - assume a peltier.

They have electric motors in them. Check out this one - you can see the wires: Shop Heat Powered Stove Fan Fireplace Fan | TheMarket NZ

I guess it's generating power to use an electric fan. Seems like just plugging it in and using a stronger fan might be worth considering?

I think someone forgot to proofread this diagram from CokemonZ link...

Mitre10 just got these in. $129 and $199.

edit: I am getting a simx heat transfer system with r1.0 ducting and extra blanket insulation will be wrapped, it's on back order at the electrician.

How ecofan works here. In short, heat is turned to power, power turns fan.

The use pieltier effect to run an electric motor - Google Link. I don't have one, but I am interested in them.

In my experience a fan on/over the fire is not about "blowing" the heat to you, they are about homogenising the air temperature in the room and eliminate stratification i.e. hot air at the ceiling and cool air at people level. The fan mixes cool air with the blazing-hot air that was otherwise rising to the ceiling, resulting in a large volume of warm air and it no longer stratifies.   

My house has an high A-frame style roof with mezzanine lounge. The apex of the ceiling (2 stories up) would get to 40 deg C while the down-stairs next to the fire languished at 18 deg C. So I put a 240v fan next to my log burner to blow over it, and now the down-stairs gets much warmer and faster while upstairs no longer gets stifling hot. It makes a huge, positive difference, but my situation might be unique. 

While they would make a difference, I'm not sure one of these thermo-electric fans would be powerful enough for my situation, but I would love to try one. 

You could probably get a similar result with a ceiling fan, but visitors would think you were mad. 

CokemonZ:

 

It's not convection - assume a peltier.

 

They have electric motors in them. Check out this one - you can see the wires: Shop Heat Powered Stove Fan Fireplace Fan | TheMarket NZ

 

This its a peltier block that generates electricity from the heat on the base and feeds it to a small electric motor.

Mine stopped working after a few years. The usual solution from the net is to replace the heat transfer paste that has broken down. So I did, but it made no difference, still doesn't work.

One of the manufactures had a some PR based on their testing many years ago. It sounds good until you see the distances involved. Basically they are only good for small spaces due to the low air flow fan.

imho just use a normal fan, it will move substantially more air for very little cost. Even better fit a ceiling fan.

JayADee:

 

Has anyone here tried one of those fans that sit on top of the wood stove? The kind that spin on their own.

 

Are they effective?

 

I bought one for ornamental reasons. I like the clever use of the peltier chip that powers them.    

As a product though, they are a piece of crap and will make no difference whatsoever. 

Edit: I should elaborate. They hardly put out enough fan/wind/pressure to really blow the air forward. The slow air coming forward out the fan just gets pushed up as it hits the air rising in front of the fireplace from the heat convection flow.  

You are much better off using a heat transfer kit or a ceiling fan. 

For ornamental/toy purposes, the average geek might get about 5-10 minutes of entertainment out of it before the novelty wears off.