UKH

Hi all, I came across something called a recoheat, which is basically a stainless steel coil fitted inside the flue of a wood burner. It pumps hot air out from the flue and claims to make the wood burner considerably more efficient at heating the room, and potentially the whole house. I was a bit concerned about creosote build up, but they claim that it doesn't significantly alter the draft rate or temperature up the flue.

Has anyone come across these? Anyone know if they are as good as they claim to be? I have a 5kW stove and only burn properly seasoned wood.

The hiss could be a bit annoying, but i could live with that if it worked. More info here https://www.recoheat.co.uk/

Not aware of them, but the basic physics say you can have something from nothing, so they *have to* affect the flue heat. By how much, and what effect that will have will depend on the tech, but if it's gaining any *real* heat (say 1kw upwards, you will be risking the flue).

I guess trying to find long term tests / real world reviews might be challenging. You could always give it a go and monitor the output? Is your fire already fed external air? Probably as big a gain to be had there? 

I like the look of things like the stovax studio air. 

Have a read of this : https://www.hearth.com/talk/threads/recoheat.193721/

My first concern was how it affects flue sweeping.

Second, if it hardly affects flue temperature , is it more effective than a £30 stove top fan?

Thanks for the link. I had read that too. Sounds like it's probably worthwhile on a less efficient stove, but potentially risky with a modern more efficient stove according to most folk on there, although the recoheating guy was pretty vigorously defending his claims.

He did come across as a but too pushy salesman, trying to bamboozle with science. I've got a rudimentary understanding of turbulent flow dynamics, and as far as I could tell what he was saying was technically correct, although seemed to make a lot of simplified assumptions. But then if the reviews are to be believed it does at least have a noticeable effect. 

My fire draws air from the room (not sure if by external fed you mean air from outside?)

Yes, both of those were concerns of myself. If his website and all the reviews are to be believed then there's no concerns there...

Apparently sweeping is not an issue, although I think it mentions that it might be for older more traditional methods, whatever that means. And the effectiveness does sound a bit too good to be true.

A basic bullshit filter for me was his claim that it "only removes 5% of the heat from the flue gas", but, at the same time puts out 1kw?

Therefore implying that the flue contains 20kw waste heat to extract....

I'm calling BS.

Oh, and the air draw - can you look into converting it into an external feed? If the air for the fire is drawn from the room, it needs replaced (usually by cold air from outside). Whereas, if you feed the fire with air from an outside vent, the air in the room stays in the room and warms up. 

I can believe it doesn't alter the temperature of the flu very much.

The coil looks to have a tiny surface area so I wouldn't expect it to catch much thermal energy. Airflow through the coil must be tiny also.

My guess is you'd need 10 of them stacked in parallel to get some noticeable heat from it.

1kw for one of these coils doesn't sound credible to me. Unless you're burning that special steam train fuel from Back to the future 3.

Errm, did you mean "can't" Ali?!

Ha, classic typo. I keep trying, maybe someday l'll pull something out of nothing and get my project done...