Added a baffle to Grandma Bear Fisher Stove (updated with 2ndary burn idea)

[pen]

Look in my avatar to see my 1981 Grandma Bear fisher wood stove. Been in service every year since install and is a general workhorse (I mean, what is there to fail).

In an attempt to save the environment and perhaps get some more heat out of less wood, I designed a baffle that a friend in a metal shop made up for me. Last night I was able to cut firebrick to fit, and install.

Here is what it looks like now. Before there was nothing stopping the flames from going directly up the chimney!

The entire thing is made out of 3/16 thick angle iron (doubled down the center). Hopefully it will withstand the heat over time.

The opening now that allows the gasses to enter into the top chamber of the stove is just slightly larger in area than the area of the 8in flue pipe exit.

It is pretty early in testing, but the first day seems to be good.

So far I am noticing that my stove surface temps are staying as high as normal for longer and on less wood.

I am also seeing my chimney pipe temperatures running lower than normal.

It will be an adjustment period as I learn whether or not it is better to leave the damper on the stove pipe wide open now, or close it some and increase my primary air intakes to maintain a sufficient flue temperature. Guess I'll be making the neighbors wonder what I am up to again by making 50+ trips out on the deck to see if smoke is coming out of the chimney.

I am going to clean the chimney today once the stove burns out later this morning so I can start on a clean chimney and see if this will change (for the better or worse) my chimney cleanliness.

This definitely is not as efficient as a secondary system, but hopefully will prove to keep the smoke down in the heat a bit longer and perhaps result in a bit more heat and cleaner burns.

My only concern is that perhaps the extra heat that is kept down on the wood because of this baffle may cause the wood to pyrolize and there may not be enough air present to sufficiently burn it. If this is the case, I am hoping that by reducing the stack damper I can increase primary air to aid with this. However, utilizing the stack damper also slows the speed of the effluent, giving it a better chance to reduce as creosote. If this is a problem, I could even remove a firebrick from the front of this, back, both, who knows.

Sooo, it may be of help, or not. But the way it is designed it can be easily removed.

Let the experimentation continue!


pen

 

[Pagey]

Nice! I certainly hope this works well for you, and I look forward to hearing your results.

 

[peakbagger]

Too bad that you didnt have primary air ports on the back side of the stove instead of the front door. Then install some secondary ports on the upper chamber and you would probably pick up more efficiency.

 

[Yamaha_gurl]

So, a baffle is only a plate that prevents all the flames from going up the chimney? Sorry, newbie alert :red: If so, I'm lucky...my fisher already has one :D

 

[pen]

So, a baffle is only a plate that prevents all the flames from going up the chimney? Sorry, newbie alert :red: If so, I'm lucky...my fisher already has one :D

Funny you mention that. My buddy who has a grandma bear "like" stove built by kodiak had a smoke shelf as well. This one simply did not.

Any chance you could take a picture of yours? I am curious to see what it looks like.

pen

 

[Todd]

Too bad that you didnt have primary air ports on the back side of the stove instead of the front door. Then install some secondary ports on the upper chamber and you would probably pick up more efficiency.

Or put a bypass plate on the rear of the baffle and a cat in the front.

 

[WES999]

The baffle looks good, I would expect you will see higher stove top temps now. Looks like you could add secondary burn tubes like I did on my stove without too much trouble.

 

[BJ64]

Neat and simple. I like it a lot!

If nothing else you added more thermal mass to the stove. I'm just a dim-wit on these things but that should do some good.

I'm excited to see how this works as well!

 

[meathead]

Thing of beauty

 

[pen]

Thanks for the kind words.

The chimney didn't get cleaned today because the snow started a bit earlier than I anticipated. I'll wait until tomorrow when things are a little calmer to climb up on the roof.

Just went from 11:15 to 3:15 on 3 medium pieces of wood. Wasn't much of a coal bed to start with either. Stove temps stayed right up in the normal range for my stove until the last 1/2 hour. That is a much longer and hotter burn than I have ever gotten without that. A typical small load for that stove is 5 pieces of wood. 3 usually won't burn for beans as it didn't maintain enough heat near the wood for a decent burn. It took 5-6 to create enough of its own critical mass to make a good clean fire.

Initial results are good.

pen

 

[Redox]

I like it! I always thought there should have been something up there to stop the flames from going right up the stack.

I hear some secondary air tubes calling your name! Know any adventurous welders?

Chris

 

[fossil]

3 or 4 perforated tubes running E-W, or a simple perforated baffle plate mounted beneath that new shelf, provided with a source of secondary combustion air, perhaps. Don't stop experimenting. Rick

 

[begreen]

Great job on improving the old gal. I agree with Rick. If nothing else put in a perforated pipe going across the front of the baffle with it's own air supply. Put some sort of valve on it to regulate the secondary air and I think you'll be pleased by the result.

 

[pen]

Thanks for the words of encouragement.

I would love to have secondary air that is adjustable since I do use the spark arrestor screen from time to time so that the fire can burn and I can watch it with the door removed. (which seems to radiate much more heat, slows down the burn, and surprisingly does not put smoke into the room at all since the addition of the baffle).

I think I am going to have to wait and see for a while how successful these results are. This device is removable as soon as the stove slows down. Even though this is an old stove and worthless to many individuals, it really did burn very well with good wood on its own. The only problem is that it consumed about 30-40% more wood!

I am a bit nervous about modifying the stove itself! I know I could always block off the hole that I would create for secondary burn tubes if it didn't work as I designed them, but that's a leap that is going to take a little bit of working up to on my part In time I suppose. Just hard putting a drill to a stove that I love even if I intellectually know the results.

pen

 

[fossil]

Think about the penetrations that already exist and whether or not you could use one of them to your advantage. For example, there's no reason secondary combustion air couldn't be fed down through the flue collar somehow...it'll go that way if the stove has a good draft, and that would tend to preheat the secondary air, which is a good thing. That way, you'd be modifying the stovepipe rather than the stove. The secondary air supply duct itself probably doesn't need to be any bigger than maybe 3/4" i.d., if that. Just a thought. Rick

 

[pen]

That is a good idea about running it down through the stove pipe. Worst case scenario I would be out a 2 foot length of pipe.

How's this for a simple idea.

Drill a hole in the stove pipe below the damper.

With a 90, Attach black iron pipe below damper (3/4in) and secure.

Create a way to make the amount of secondary air adjustable here.

Run the black pipe down through the stove pipe, into the stove and through the center firebrick in my baffle by drilling a hole.

Tee off to the left and right. Drill 3/16in holes every 1 1/2 inches along pipe

Do you think black iron pipe would hold up? I don't have easy access to stainless. Any thoughts as always are welcome.

pen

 

[Hogwildz]

That might be a tough sell.
The secondary pipe in the exhaust stack is going to be fighting the draft upwards, and may end up sucking air & gases into the secondary tube, rather than blowing super heated air out out create secondary burn.

 

[Adios Pantalones]

I'd be tempted to run the air from the bottom. Hot air rises. You'll be fighting gravity if the intake or some run of the pipe goes too far above the secondary tube. The secondary tub might then become a secondary exhaust tube.

 

[Peter B.]

pen:

I respectfully disagree with the last two posters.

A number of years ago, I installed a rudimentary secondary air system in a Jotul 118 - through the stovepipe and down into the stove. It drew fine.

Some folks seem to think that smoke 'pushes' it's way up the chimney, and will use any available seam to leak out. The truth is otherwise. Basically, if you have adequate draft, you can visualize your chimney as a huge vacuum cleaner... and you can introduce air at any virtually any point on the stove (or pipe) and air will be drawn into the system.

Only when the draft is *NOT* adequate will there be a problem with smoke exiting from the 'wrong' hole.

--

Black pipe is likely to last a few seasons, but may oxidize internally and clog the secondary drillings/passages. I've used copper for my 'experiments' in past, which has the same problem, but is a little easier to work with... and can be swapped out for stainless once you've arrived at a final design.

Looks like a fun project, by the way.

Peter B.

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[Hogwildz]

Yes and with that vacuum cleaner like suction of draft going up, how is the secondary tube going to be pushing hot air for secondary combustion out those jet holes? It won't, it will also be sucking air into the holes rather than blasting out. The only secondary that may or may not happen is going to be in the stack, not in the firebox where you want it to burn the gases from the wood & make the heat inside the stove.

 

[jacksnipe]

I'm thinking about installing one of these items in 1/2" NPT & drilling a hole into the firebox to accept it. if it doesn't work out a recessed plug could be installed to block it off.
I hope the picture comes through so you get an idea what I'm thinking about.

 

[pen]

Yes and with that vacuum cleaner like suction of draft going up, how is the secondary tube going to be pushing hot air for secondary combustion out those jet holes? It won't, it will also be sucking air into the holes rather than blasting out. The only secondary that may or may not happen is going to be in the stack, not in the firebox where you want it to burn the gases from the wood & make the heat inside the stove.

The pipe would not be open at all in the stove pipe. Rather my hole for getting fresh air would simply be in the stove pipe and the sealed pipe would then run down into firebox through the baffle.

My thought was that cooler air moves towards warmer air. As such, with the opening being outside, and the pipe warming its whole way into the burn chamber that it would have the natural draw regardless of being up or down. But that was my reasoning and it has proven to be less than sound at points!

Keep hashing out ideas, the more the better.

Thanks guys

pen

 

[Peter B.]

Yes and with that vacuum cleaner like suction of draft going up, how is the secondary tube going to be pushing hot air for secondary combustion out those jet holes? It won't, it will also be sucking air into the holes rather than blasting out. The only secondary that may or may not happen is going to be in the stack, not in the firebox where you want it to burn the gases from the wood & make the heat inside the stove.

Again - respectfully - you're wrong.

I run a simple secondary tube in my current stove through a drilling near the flue outlet, and *down* into the stove.

I would see smoke from the tube orifice if the tube was 'sucking backwards'. I don't... and the burning match/cigarette/incense stick proves air is going *in*.

Peter B.

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[Peter B.]

I'm thinking about installing one of these items in 1/2" NPT & drilling a hole into the firebox to accept it. if it doesn't work out a recessed plug could be installed to block it off.

Unless 'strategically located', the fitting alone won't do much (if any) good... and if the air isn't preheated at all you're just introducing an extraneous hole in the stove.

You'd want to attach a tube to the fitting (at least), extending into the stove (and the smoke path)... and figure out some means of heating the air before it leaves the tube.

Peter B.

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[Todd]

I wouldn't fart around with secondary air tubes if that was my stove. Instead I would make a slide in cat in front of the baffle similar to what Peter did with his pot belly.
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