Fisher catalyst mod

[albert_k]

Hi gang!
i’ve got a Baby Bear in a Northern Minnesota cabin that’s about 320 ft.² and not terribly well insulated. As you expect, I struggle from burn times at night in this little stove. While installing the baffle upgrade last week, I came up with an idea for a removable catalyst, and I thought I would throw it by you. currently the baffle plate goes from below the rear exit, Slanted upward toward the rear upper joggle in the middle top plate. This allows the necessary 2+ inches of air gap for me. However, as I was thinking about it, I could cut a round hole in that plate toward the front of it and install a round catalyst. I can then install a second smaller plate (about 13” wide by 3” deep in front of it that acts as a bypass when tilted up, and closes of the 2” exhaust gap when down, forcing the exhaust through the catalyst when operated. The only exterior modification I would think I would have to do would be to drill a hole in the side of the stove, right where the low deck joggles to the high deck. install a small but heavy duty steel tube with a joggle bend on the inside to raise and lower the bypass plate when rotated. this tube would protrude a couple of inches out of the stove and have a handle.. the end of the tube sticking outside of the stove would be threaded and have a slot cut in it. A threaded knob would then be installed in the end of the tube. Similar to the front air inlet, as you unscrew the knob, more air gets into the catalyst. thoughts?

 

[MongoMongoson]

If you are looking for a metal working project and enjoy experimentation, then I say go for it. Any hole you put in the steel body can be filled if it doesn't work out. It sounds like something that will take some experimentation and fiddling. If that is what you are after, you can stop reading right here and just get to work.

Otherwise, I have other suggestions.

I would think you should be able to roast yourself out of the place with a baby bear if it is only 320 sq ft. I know the stove is small but even so, the space you are heating is tiny... before you go to bed, do you have a nice coal bed established?

If you don't want to do the old smolder/creosote factory with your old style stove, one thing you can do is to get a nice big pile of coals built up and have those carry you through the night. You might need to have the windows open while you are building your coal bed by feeding in lots of hardwood as your flames burns down and you want to make more coals. What are you burning? I burn popple for quick max BTU output without coal overload, but sugar maple and ironwood to build overnight coals.

With such a small space, it will be difficult to get a stove (new or old) with a firebox big enough to carry you through the night that is not so big that it turns the place into a sauna while you are feeding it. Consider sealing the place up and insulating it rather than trying to modify your stove.

My place in the UP isn't much different than yours. I have 400 sq ft and use an old Quaker Buck to heat it. I have the advantage with that stove of having a deep firebox where I can build coals in the back and pull them forward before bed to have them burn through the night. Even so, it can be cold in the morning with just the wood stove burning.

I did not add insulation, but I did seal everything up inside and outside around the windows, doors, and ceiling to try to keep mice out. What a difference that made! I used Great Stuff with hardware cloth for big gaps and caulk for smaller ones. My main goal was to keep mice out (thus the hardware cloth), but while I was there with a caulk gun ready I sealed up any gap I could. It worked. Not one mouse for the last 3+ years. After I did it, I noticed the benefit of holding more heat overnight .

 

[mellow]

At one time quite a while back I retrofitted an older Sierra stove with a catalyst. It was a cool project and it did cleanup the exhaust. The thing is if you are going to do it right you need to have the cat in a place where you can absorb the energy from it and have a fan displace that to the room. That is why you see cats on the top of stoves so that heat carries to the fan tunnel that is above area. That cat will get 1200+ degrees so you don't just want all that going up the chimney. Look into modern designs of cat only stoves to get some ideas if you go this route.

 

[MongoMongoson]

Good points from mellow.

I was thinking about this more this morning. I think the OP would also need to have temperature probes to understand what is happening. The Fishers are black boxes that you can't see inside of. How would OP know if the catalyst working? Maybe by the stove top temperature on the upper step vs the bottom step, but OP would be better off with a probe to measure the catalyst temperature and of course a stove pipe probe.

With my old Fisher clone All Nighter, I often had the stove top pushing the limits for temperature and the stove pipe was not, so I think mellow's point about getting heat off the stove top is really important.

 

[albert_k]

all great info! I was at the cabin this weekend and temps dropped to -17F plus wind factor (20-30mph constant wind overnight)
Here are my observations:
The 13x9” 1/2” thick steel baffle was a total game changer! So grateful to have seen that post! Before I installed it, my temperatures would swing wildly and I was constantly attending the stove. Now it’s simply locks in. at between half and 3/4 of a turn open, the flue thermometer is barely in the green, while the thermometer on the lower top plate in the center reads just at under 700°. It remains that way for nearly the entire burn and then slowly goes down.
I burn mostly birch.
The cabin never got above 65°
I consider the stove output now to be a finite number rather than a variable. The way that it’s set up currently release a certain amount of BTU per hour consistently as long as it has fuel. Everything else is about outside temperature and insulation factor of which I have very little. I think I simply need to insulate the building better..
I would however, like to try the catalyst and plan to because the 13” x 2.5” x 1” thick catalyst tucks up perfectly in that bend on the fisher stove where the lower top plate transitions to the higher top plate.
My only objective with this change is to extend burn times overnight and use less wood. Also, it’s nice to know that if I took the catalyst out due to failure or for some other reason, I know exactly how this woodstove will work with just the baffle plate..

 

[albert_k]

I should have mentioned… My usable burn time per full load of Birch splits is about four hours from when it gets up to temp until the stove Topp drops to 400° or so. If a catalyst will stretch that to six hours. I could actually sleep a full night.!

 

[mellow]

What is your plan to harvest the heat from the catalyst if you want longer burns? How are you going to protect the catalyst from flame impingement?

Just adding a catalyst doesn't magically make it burn longer.

Take a look at the setup of Buck Stove model 91, they have the cat protected with a heat shield and have a fan running over the top to harvest the heat: https://buckstove.com/model-91/

 

[albert_k]

good questions and I appreciate the observations! As a test, I pointed a box fan at the woodstove from about 5 feet away. It worked as you might expect. It drove the surface temps down a lot and moved warm air into the open floor plan tiny cabin. The idea with the catalyst is that it would pivot up into that bend in the upper lower top plate transition when in bypass mode then using an external lever, I could rotate it down to interface with the edge of the baffle, forcing the smoke path through it. I hear what you’re saying about a reflector. I think I’m just gonna have to install it and take the laser thermometer and see what’s going on. I was really hoping it would extent burned times. I can throttle the stove down to like 600° which does extend burn time but at the expense of being right in the creosote zone on the stove pipe. I considered using double wall pipe all the way down to the stove,to keep more heat in the pipe at a lower burn, but then don’t I lose all the radiant heat from the single wall stove pipe going up to the ceiling? I’m not really an expert at any of this so it’s all just getting advice from you guys and trying things.. and I really appreciate the advice!

 

[albert_k]

so I guess I was hoping that I could burn the stove at a lower temp and that the catalyst would clean up the smoke so that the flu temps were less critical for creosote buildup. Would this not be the case?

 

[albert_k]

It’s an interesting Catch-22 I’m in. Currently in order to get clean Burns in the flu and minimal creosote i have to run the stove as pictured. Having taken the pipe system apart several times. It does stay pretty clean after the baffle versus before. burning it this way, would – I believe – give me the necessary heat with more building insulation. However, as mentioned, burning it this way does not give me the burn times I was hoping for. A larger stove would not fit, and I’m sure would drive me out of the cabin with heat. I believe and I’m hopeful that running it a little lower with good insulation would achieve my heating goals and extend my burn time as long as I can solve the creosote issue I mentioned. That’s what keeps bringing me back to the catalyst solution. I’m just really hoping I’m not on a wild goose chase. interestingly, switching the baffle plate out to an 8 inch plate seems like the solution for the shoulder seasons as the balance between stove, temp and flu temp shifts dramatically. More heat is ejected through the pipe and less is retained by the stove. A good thing when temperatures aren’t so bitterly cold.