Modifying a Columbus Ironworks 34 Big Box for maple evap

[Shsesc]

Hi, I have an odd question for you all. This is not in my house. This is in my back yard. Please help.

Note, I know this is an antique, I don’t want to damage it, everything Ive done is removable so far.

I got this stove in rough shape from a friend to evaporate maple sap in hotel pans. The problem is the pan sits over the removed top and the fire is hottest right under the flue outlet.

I added fire bricks because it was burning so hot and I want to add a baffle to redirect flames under the pan. I was thinking I could put it on top of my brick retention device I made.

I’ve evaporated a little syrup on this with the pan inset into the opening and it is slow. I’m moving to a double steamer pan over the top of the whole opening and I need help designing a baffle. Should I use angle iron, angle iron holding up fire bricks, thick sheet metal? Some combination? I get the back of the stove box up to 800f or so measured by k type thermocouple, and the sap was just barely boiling. I have a damper on the singe wall flue, and it helps a little to close it off slightly, but not enough.

I have only 7 trees and only tapped on 2/13, but I need to get this figured out soon because I’m sitting on 70 gallons and counting of sap. The clock is ticking. The syrup depends on it...



Thanks for any assistance you can give.

 

[Shsesc]

So in experimenting with different size baffles, if I make it extend too far toward the door, the fire burns poorly and smokes a lot out the flue. If I put only a 6”. Piece of sheet metal from the back of the stove it seems to burn like normal. But the hottest part is still not under the cook top.

 

[EatenByLimestone]

When i used to boil it down, most of the time i didnt have a boil until the very end, as the water was steamed off. Are you trying to hurry the process too much? If you want faster product, you can always extract the water with a RO setup.

 

[Shsesc]

When i used to boil it down, most of the time i didnt have a boil until the very end, as the water was steamed off. Are you trying to hurry the process too much? If you want faster product, you can always extract the water with a RO setup.

I am building an RO, the pump comes tomorrow, but yeah, It should be boiling the whole time. It foams at the end if you take it to far on the wood stove, I usually finish indoors for more control. No reason not to boil it the whole time. Water boils at 212, the boiling point raises as it concentrates at the end it is like 219 or so depending on elevation and barometric presssure and what brix you want to arrive at.

If I let it just simmer I end up boiling from 7am to 7pm and only get 15 gallons of sap evaporated. If I can boil it will improve my evaporation rate in addition to the RO removing a good amount of the water.

 

[coaly]

How much stove pipe do you have on the stove? That is what makes air rush into the stove to make it burn.

The baffle should be angled from the back on the brick retainers to higher in the front. With a proper chimney, a flat baffle is OK, but the baffle adds resistance in the firebox. The chimney makes negative pressure and the connector pipe, elbows, damper, baffle all adds resistance, slowing draft. You don't have that engine to create the negative pressure you need. Angling baffle upward reduces internal resistance increasing flow. This flow is what allows atmospheric air pressure to PUSH air with oxygen into the stove, making it burn.

The baffle should be 1/4 inch thick steel plate.

The space near the front the exhaust travels through I call the smoke space must be no smaller than the square inch outlet and flue size. (6 inch being 28.26 square inches) This is normally adjusted to the chimney needs. (indoor / outdoor, masonry, insulated / non insulated) since the heat required by each chimney is different. Just start with the minimum or stop baffle under stove lid for direct flame contact. Experiment with the flue pipe damper to control velocity through stove for the flame at this area you want.

Normally the chimney getting hot and staying hot inside is what causes the air to move through the stove feeding the fire. A flue pipe damper is a chimney control used to slow velocity of rising gasses which controls the chimney. Controlling chimney affects the stove by slowing it down. It must have the correct negative pressure at the stove collar. You won't be doing that with a pipe or two on the outlet. That said, you can only control the flow up the pipe with a damper until you get the flow you want across the top of the stove.

 

[Shsesc]

Thanks Coaly for the thorough response!

I have 8 feet of single wall 6” stove pipe, I’m outdoors.

I use the damper when the single wall pipe reads more than 610f which is what my non contact IR can read max. It seems to run best with the pipe surface in the 500s. I get good draw until I extend the baffle too far toward the door. Even though there is probably 48square inches of area cross sectionally above the baffle when flat and below the stove top or pan. That’s rounding the stove to 12” wide and the depth from baffle to pan to 4”.

Would a small blower help overcome the drag on velocity of a flat baffle? I would probably update the design later, but the clock is ticking with this warm weather. I keep putting sap—cicles in the barrels to keep it cool.

 

[coaly]

I would put something non combustible under the door end of baffle so it allows heat to rise across it faster. Raising an inch to 1 1/2 still gives you enough opening for your exhaust size. Think of the stove turned upside down in your head. Heat now acts like water running downhill. The heat source being the fire is like a water faucet. You want the water to run down the baffle spilling over the edge through the open hole.

Normally burning in a stove should be on firebrick in about an inch of ash to slow oxygen from getting to the bottom of logs increasing burn time. For a much faster fire you can elevate fuel on something like steel fence posts cut to the length of stove. This gives logs more air under them for a much faster, hotter burn. A grate should only be used in an open fireplace to accelerate fire and reduce smoke. In the case of needing more instant heat this may work for you. Of course it will shorten the duration of burn considerably, which is what you don’t want in a home. Coal cook stoves get their intake air from up through the grate which burns wood very fast, but needed for cooking.
I bought a Fisher Papa Bear to recondition for someone years ago that was used for syrup for many years. The difference is a steel stove is much more forgiving of temperature changes. The single door Fishers have a much larger cook top than double doors and the baffle is on a steep angle in the back creating little resistance. When the two air intakes are open they sound like an oil burner inside and heat up quickly. They have no direct flame contact so the top is ran hotter for cooking.

If you get it hot enough, you should be able to keep it boiling on the closed stove top. I’m not familiar with using your model box stove, but that style keeps a rolling boil in normal size pots on the closed stove top once up to temp. You can experiment sliding the baffle forward allowing some to escape directly up stack too. This is loss up the stack, but creates more air movement coming into the stove. It’s all about getting oxygen into the box. If you can’t do it naturally, with atmospheric air pressure it can be done with a small induction fan.