Capturing Waste Heat from a Woodstove

[01-7700]

Still in the thinking stages on this project, but I've got an idea of what I want. This is a diverter that will sit on top of the wood stove. It will allow smoke to go right up the chimney during startup and will allow the cleaner afterburn to circulate through a masonry mass with the turn of 2 dampers. I have no idea how to size the masonry mass but think I can capture a lot of heat this way. Does anyone have advice on using something like this ?

 

[Ign]

All I'm seeing is an X and I'm not gonna be much help anyway.........but I can just say I use a double barrel kit with a Magic Heat. Between the upper barrel and the heat exchanger I imagine I'm using a great deal more heat than without those two things.

Last winter my Magic Heat went down and I definitely noticed it was harder to heat my shop.

But as for masonry anything, I'm no help.

On one of the recent Homestead Rescues he attempted to cobble together stove pipe in a trident shape, the theory being most of your draft goes straight up but the left and right forks just kinda hold hot air. I thought it was an "ok" idea, and they claimed it worked. But of course thin metal pipe simply won't hold heat like masonry as you propose.

 

[finn]

Don’t forget that removing too much heat from the flue will promote creosote build up in the chimney of a wood fired stove.

Modern catalytic stoves are a better route to pursue than cooling the exhaust of your grandfather’s smoke dragon.

 

[01-7700]

Don’t forget that removing too much heat from the flue will promote creosote build up in the chimney of a wood fired stove.

Modern catalytic stoves are a better route to pursue than cooling the exhaust of your grandfather’s smoke dragon.

I have a modern catalytic stove. The divertor is for use after the smoke has cleared from the exhaust.

 

[Unhdsm]

I bet the exhaust temp of your modern stove is relatively cool already. Mine hovers around 200f and that is with a Cat that needs replacement next year. You need the exhaust a little warm to promote draft. My guess is with good burning practices you are already getting everything you can out of the firewood. If you have a lot of heat going out the stack with an EPA stove something else is wrong. Remember- the stove doesn’t push air, the chimney pulls it. It’s an active, working part of the system.

 

[TractorJeff]

A soapstone stove is similar to what you are thinking. I have a woodstove insert in a brick fireplace which runs 24/7 that will radiate heat back out of the brick if the fire goes out.
But not as much heat as you are hoping to capture and release.
Like 45 degrees instead of 30'ish.

 

[Richard Cranium]

I have seen what is called a heat robber, it mounts in the chimney, and has small tubes that goes through it and then a fan to push the heat out.

 

[zak77]

I wouldnt cool down the flue gases or obstruct them. I've seen a flue where my buddy was really damping down his stove and within a month his 6" single wall was almost plugged, i'm amazed he didnt have a chimney fire. I burn about 7 cords a year and only clean my chimney once a year at the end of the season because there is very little buildup since i burn the stove the correct way. If you are going to try and squeeze every bit of heat out of the flue gases, and slow them down then you're going to having buildup issues.

Instead, i'd look at building a surround for the stove and install a blower. My buddy used to heat his 6,000sq ft shop with a stove and blower. Granted that stove took a 48" log but he built it next to a concrete wall and put it on a concrete block stand which both acted like massive heat sinks. I've seen people build concrete block walls around stoves to hold the heat.

 

[Ign]

I have seen what is called a heat robber, it mounts in the chimney, and has small tubes that goes through it and then a fan to push the heat out.

Magic Heat and the competitor is Miracle Heat. This is called a heat exchanger; really the same concept as the heater core in your car.

https://www.garagejournal.com/forum/showthread.php?t=357756

 

[01-7700]

That's OK, I guess I really just wanted to show my fancy 3d renderings. I'm not going to do this based on advice I got. Thanks everyone.