Wood stove modification project

[justincorhad]

Hey all, just thought I’d share something I’ve been tinkering on the past few days. It’s not pretty, it’s far from complete and definitely needs some tweaking.

So I’ve had this small old wood stove sitting in storage for the last few years. It’s in really rough shape, the baffle box is warped, cracked and rotted, as was the secondary air tube. It was cracked around the door, and the glass had been shattered and replaced with a steel plate.

Given the amount of work needed to put this stove back in working order, I figured I’d do some experimenting with it instead.

I Cut a hole in the back of the stove on the bottom side. I built a fuel hopper which I attached to the back. The hopper measures 21” wide, 7” deep and 17.5” tall.

I the. Blocked off the original primary and secondary air ports. Primary air now comes in the back of the fuel hopper.

I then built a secondary air manifold which sits on the floor of the hopper, with multiple upright tubes with holes drilled in them. This manifold doubles as a grate. It’s thin mild steel so I’m not expecting much life at all out of it, but for experimental purposes it will do just fine.

I took the door from my other wood stove and rigged it up to fit on this stove, because who doesn’t love to see what’s going on in there.

I’ve only the fired it once so far, it does work, in the one picture you can see the secondary combustion from the holes in the tubes.

I still need to build a lid for the hopper, I need to drill the secondary air holes bigger as well because even though they do light off they can’t quite keep up and I still end up with some smoke out the pipe.

I also need to move the primary intake, right now is sitting about 4 inches off the floor on the back of the fuel hopper. I was originally thinking of a cross draft still, like the Sedore, however I found whenever I block the top of the hopper only some of the flames keep moving forward through the secondary air grate while a lot of flame ends up going up the hopper instead. It never does this with the hopper uncovered so I think I may move the primary air closer to the top of the hopper for more of a downdraft effect.

Anyway that’s all I have so far. Any thoughts on this cross/down draft, rear loading stove?

 

[marty319]

I hope you only burn that outside.lol

 

[justincorhad]

I hope you only burn that outside.lol

Lol why’s that? I’ve only fired it outside so far, but I’ve done a lot of wood stoving experiments in my shop as it’s just a concrete and steel building with a large exhaust fan. Obviously I’d never use any of these devices to heat with as my very pricy home insurance would be void if I did. I more just enjoy the tinkering part of it.

 

[begreen]

What was the make and model of the stove before the tinkering? Napoleon?

 

[Prof]

Looks interesting!

 

[justincorhad]

What was the make and model of the stove before the tinkering? Napoleon?

Honestly not sure, the people I got it from had overfired it so badly most of the paint was flakes off and any labels were unreadable. My guess is either a Napoleon or an older Drolet

 

[justincorhad]

Looks interesting!

Thanks! I’ve always liked the downdraft and cross draft stoves, but I wanted to see if I could make one where the fire was visible, cause that’s really one of the nicest parts of having a fire.

 

[Prof]

Thanks! I’ve always liked the downdraft and cross draft stoves, but I wanted to see if I could make one where the fire was visible, cause that’s really one of the nicest parts of having a fire.

I never scoff at a guy willing to try something new. I have a great masonry heater in my living space. I'm sure the first person who had that idea was considered crazy by some. Best of luck on what looks like a cool project! I agree about the visible part of the fire. I can literally sit for hours watching a fire. So much better than anything the internet has to offer!

 

[Poindexter]

Kudos for exeperimenting. What is your goal?

 

[justincorhad]

Kudos for exeperimenting. What is your goal?

My thinking is that secondary burn stoves usually:

1) aren’t as clean as catalytic stoves

2) can’t burn as low and slow as catalytic stoves

They usually can’t burn as low and slow because the wood gasses need to reach 1200f or more before they will ignite, requiring that the stove burn a little hotter/faster for the secondary burn to work properly.

I was thinking that because the hot coals are at the bottom and the gases must travel down through them that it would keep them hot enough to ignite, but also allow the stove to be turned down a lot more and burn much slower and still stay clean burning.

My theories have yet to be proved, and I need to tweak the stove some more and make it more air tight. But you never know if you don’t try.

 

[bholler]

My thinking is that secondary burn stoves usually:

1) aren’t as clean as catalytic stoves

2) can’t burn as low and slow as catalytic stoves

They usually can’t burn as low and slow because the wood gasses need to reach 1200f or more before they will ignite, requiring that the stove burn a little hotter/faster for the secondary burn to work properly.

I was thinking that because the hot coals are at the bottom and the gases must travel down through them that it would keep them hot enough to ignite, but also allow the stove to be turned down a lot more and burn much slower and still stay clean burning.

My theories have yet to be proved, and I need to tweak the stove some more and make it more air tight. But you never know if you don’t try.

The problem there is coals are usually much cooler than 1200 degrees.

 

[justincorhad]

The problem there is coals are usually much cooler than 1200 degrees.

Really? I’d imagine the coal would be probably much hotter than 1200f, hence why steel grates degrade/deform

 

[justincorhad]

Found this, may be wrong may be right, but I was fairly certain charcoal burns at very extreme temperature.

 

[bholler]

Found this, may be wrong may be right, but I was fairly certain charcoal burns at very extreme temperature.

Yes it can burn that hot given the right conditions. But generally coals in a wood fire are nowhere near that temperature.

 

[justincorhad]

Yes it can burn that hot given the right conditions. But generally coals in a wood fire are nowhere near that temperature.

What temperature would they be do you think then?

 

[bholler]

What temperature would they be do you think then?

It depends on air flow ash content and many many other variables.

 

[stoveliker]

I have experience judging the temperature of glowing objects by their color (as verified 1000s of times with a pyrometer - this was part of my daily work for 15 yrs). Coals to me look like they are around 700 C, which if I recall correctly is about 1300 F. Indeed an aluminum can easily melts in an outside fire pit. Aluminum melts at 1221 F. (I don't know the melting temp of the alloy used in cans, but I am pretty sure it's higher than for pure aluminum).

This suggests that coals are indeed at least close to 1250 F.

But, that is theory. Let the experiment be done

 

[Poindexter]

Can you easily move the primary air to under or beside the coals?

I am routinely seeing 1200-1400 dF in my BBQ ccokers, with a tuyere and a hairdryer for forced induction, but from underneath.

I owned one vehicle with side draft carbs, it was a pain in the neck.

 

[begreen]

I owned one vehicle with side draft carbs, it was a pain in the neck.

I had several old Volvos, a Saab and a Jaguar, all with SU carbs and got very good at tuning them. Once set up properly they didn't need much tinkering.

 

[gthomas785]

This is so cool. I have dreamt of making something like this, but never had the time or I guess I should say it never made it to the top of my priority list.
I think the lid on the hopper will make a huge difference in the amount of secondary air being drawn in. Don't mess with the hole size too much until you see the effect of that..
You're testing this outside, on what chimney? how tall is the stack? That will also have a major effect on performance.

Looking forward to more updates especially what happens when you add a bigger piece of wood or two.

 

[justincorhad]

This is so cool. I have dreamt of making something like this, but never had the time or I guess I should say it never made it to the top of my priority list.
I think the lid on the hopper will make a huge difference in the amount of secondary air being drawn in. Don't mess with the hole size too much until you see the effect of that..
You're testing this outside, on what chimney? how tall is the stack? That will also have a major effect on performance.

Looking forward to more updates especially what happens when you add a bigger piece of wood or two.

Thanks! Yeah I definitely have to make a lid with a seal to make sure it is air tight and finish welding up all the gaps.

Actually I already enlarged the holes and it made quite a large performance boost in terms of clean exhaust. The finicky part so far is getting the primary air to flow downward without upstruction.

I currently don’t have it hooked to the shop chimney cause I need someone to help me move the big heavy fisher out of the way. So I just have about a four foot piece of chimney pipe venting into the shop (ventilation fan on and shop door open of course). If I get time and some help I may hook it up to the shop chimney this weekend and see how it does.

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