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

Peter B. · Dec 23, 2008

brooktrout said:
I just wanted to say congrats on modifying your stove and especially for getting so many responses and ideas. All three times I tried to bring this up all I got were a bunch of pessimists saying don't mess with your stove.

There seem to be enough of us here interested in keeping our older stoves alive that the Moderators might consider another forum 'Room' strictly for mods to pre-EPA stoves.

(Hint, hint.)

Peter B.

-----

brooktrout · Dec 23, 2008

Peter B. said:
brooktrout said:

I just wanted to say congrats on modifying your stove and especially for getting so many responses and ideas. All three times I tried to bring this up all I got were a bunch of pessimists saying don't mess with your stove.

Click to expand...

There seem to be enough of us here interested in keeping our older stoves alive that the Moderators might consider another forum 'Room' strictly for mods to pre-EPA stoves.

(Hint, hint.)

Peter B.

-----

Here, here- well said! Throw another shrimp on the barby!

Hogwildz · Dec 23, 2008

pen said:
Hogwildz said:

Since you already have the angle iron framed out for the baffle, why not make a secondary baffle like PE and some other manufacturers make?

Click to expand...

Are you talking about a drilled baffle plate that would rest just below this one?

pen

Kind of, its more of a box with an 1" or so space inside, then holes/jets along the front face and a few strategically placed along the bottom. You could put it in place of the baffle you have there, and have secondary/baffle all in one. No added space taken up, or not much. You already have the angle framing for it there. Then you just ened a way to get air to it. PE's have a vertical channel inside on the back of the firebox. I am sure you could drill/tap some sort of hole with control in such a channel.

Hogwildz · Dec 23, 2008

Peter B. said:
Hogwildz wrote:

>Mayer I am misunderstanding.
>Pen just stated he is not drawing the secondary air from the exhaust flue
>if I read it correctly, but from an outside source separate from the
>exhaust. That I can understand.
>Is this drilling you speak or separate from the exhaust gases? Just curious.

I think you did misunderstand me, Hogwildz.

--

This still seems relevant to the thread so... I offer this simple example, which (I think) illustrates the idea.

If you drill a hole in your flue pipe and you have adequate draft, room air will be drawn into the flue through the hole.

If you put a tube of some kind partway through the hole in the flue (and the fit is tight), the tube will draw room air into the flue.

If you extend the tube through the hole in the flue down into the stove, it will still draw air... into the stove.

The extended tube will have at least a minimal heating effect on the air flowing through it. This is, in effect, a very primitive secondary air supply.

It also avoids drilling holes in the stove itself... which pen said he was reluctant to do.

In my case, instead of drilling through the flue, I used an existing hole near the stove outlet flange (one of three such holes that originally could be opened or closed to help slow an overdraft). I sealed this hole to a 3/4" copper elbow (open to the room), and added a length of copper tube down into the stove. Again it's a rather primitive arrangement, but in fact, it helps some. My stove doesn't have a glass door, so I can't see what's happening inside, but with all other drafts closed, under the right conditions, I can hear flame igniting from the air fed through the secondary.

Peter B.

-----

That makes perfect sense , and now I know I misread.
I completely agree now that I understand. I myself would be a lil hesitant to drill into the fuel pipe, in case of chimney fire etc.
But that is a personal preference, which each has their own.
I commend you guys with the older stoves and coming up with designs to help them burn better and more efficient.
I personally still think a baffle design similar to PE's and a couple other manufacturers will take up a lil less firebox space by doing the job of both baffle & secondary burn tubes all in one.
And honestly, I pack my stove to the gills. Many times up against the bottom of the baffle. I would prolly bend the tubes since I am used to the stainless baffle box up there. I admit I may have to get used the the tubes once I get the Englander I have sitting here installed and running along with the Summit also fired up. There best be no lack of heat at that point.
If my old Fuego Flame wasn't such a POS, I would toy with baffle/secondary design in it. But its junk and more suited to make a smoker of some sorts, or scrap when steel goes back up.
Keep us posted on the progress, and thanks for your patience in helping me understand what you meant.

Peter B. · Dec 23, 2008

pen wrote:

>While I love the added heat gained from my wood, what I am not happy with
>is my flue gases. I now have smoke !!!

I never did before except for
>about 10 minutes after a reload. From then on out, it would be nothing
>but heat waves. Now, I am getting 30mins on an average load to 60-75
>minutes on an overnight load of white smoke from the chimney. All the
>while the stove is producing killer heat and the chimney is about 350
>degrees (normal).

...and...

>I have discussed the smoking issue with the metal shop buddy who built
>this for me, and he believes even with the added smoking that I am going
>to find less 2nd degree creosote in the chimney since I am no longer
>needing to use my stove damper and the velocity of my flue gasses will
>have increased.
>
>Even if he is correct, the smoking issue bothers me from a smell
>standpoint (I like my neighbors) and an environmental standpoint (no tree
>hugger but I don’t like making a bigger impact than necessary).
>
>My thought is that a simple secondary, while it may not be perfect, may
>add enough extra air in the back of this baffle to help better burn this
>smoke I am finding.

--

You've likely read this here before, but most people say white smoke that dissipates to the surrounding air quickly is likely (mainly) steam from the moisture in the wood. If it's dark and lingers (and has any odor to speak of), that's 'real' smoke.

Again, I'm far from expert, but I'm inclined to think that yes, the secondary _should_ help burn off the 'added' smoke.

Also, I might continue to use the flue damper judiciously. You don't really want a rapid velocity out of the stove proper... but rather a semi controlled 'reside time' within the stove to help mix volatiles, heat and air for complete combustion... before the exhaust enters the flue.

Peter B.

-----

WidowMaker · Dec 23, 2008

glfporsche said:
I don't want to drag us too far from Pen's mods; but to answer a few questions: My secondary air tubes are in fact 3/4 inch. The baffle is McMasterCarr part number 93595K73. It is a ceramic board made of aluminia and silica. It has the consistancy of foam, very low density and soft, but it can take 2300 degrees F, and is a very poor conductor which means it reflects heat back into the fire box. It is mounted at an angle, which I regret as it makes it harder to get the wood pushed all the way back. The baffle is about 4 inches from the inlet of the stove pipe.

To comment on Pen's conserns on adding more secondary air, and that leading to overfire. I actually believe that you can add more secondary air right at the top of the baffle and this will burn off the smoke but will not increase your temps all that much, and not increase your burn rate. The bulk of the air that's injected right at the baffle does not seem to get down to the main fire and thus does not seem to increase the burn rate.

I more than quadroupled my secondary air supply when going to the stainless tubes. I use a little less primary air now but not four times less, and the burn rate is about the same. Actually, I find it harder to overfire now.

I've updated with some flame picts: http://glfporsche.smugmug.com/gallery/6450885_NdHjA

If you look closely, the picts at the bottom are with the stainless tubes and much increased secondary air. You can see a contionus ribbon of flame coming off the rear most tube. The secondary air enters the at the passage welded (poorly) to the side of the stove.

Kris

====

Absolutely GREAT flame shots. Looks like you could be a consultant for the Devil and the Fires of He77...

Holy OVERSIZED 2ndary air jets....

I was with you till pict #25 thru 30, what is that part and where does it fit in side the stove, what function does it serve??

fossil · Dec 23, 2008

Peter B. said:
...There seem to be enough of us here interested in keeping our older stoves alive that the Moderators might consider another forum 'Room' strictly for mods to pre-EPA stoves. (Hint, hint.)

Not the Moderators you need to try to convince about that, we're just janitors, and we serve at the pleasure of our beloved Webmaster, Craig Issod. Put your idea in a post in The Suggestion Box forum, he's really good about reading and responding to such things. Rick

Peter B. · Dec 23, 2008

Rick:

Thanks for the heads up... I'll get to it.

--

Parenthetically, I might also ask Mr. Issod to 'tear down' this site... it's becoming addictive for me.

And I can't afford still another addiction.

Peter B.

-----

EddyKilowatt · Dec 24, 2008

Nice job on the baffle, Pen. Interesting discussion about secondary air, also.

I have a pre-EPA, too -- a Jotul Model 8. It's basically a big hollow box like Pen's Bear, but did come from the factory with a short-ish baffle made of cast iron. My mods so far have been firebox insulation: I added a layer of ceramic wool (chimney liner wrap) on top of the baffle plate, and some more behind the cast-iron liner plates in the lower part of the firebox (where the Bear has firebrick in Pen's first post). I'm a little concerned that higher operating temps will shorten the life of the cast parts, but in fact I believe that Jotul added similar insulation along the road toward cleaning up the Model 8 -- and I can report that it definitely burns hotter and cleaner with the hotter firebox.

So with that done, I've been thinking about a secondary air retrofit, too, since I get more smoke than I'd like during the first third of each load, especially while dialing down the air.

There's a shop down the road from me that does stainless fab, and boat railings and stanchions in particular, in 316 stainless tube. Since I have few metal fab skills of my own, I've been working with what they're good at. My current plan is for a single piece of 1" OD tube, bent into the shape of a square-ish 'U' about two feet wide and one foot long, with both ends going thru holes I'll drill in the back wall of the firebox, just below the baffle. I'm not eager to drill the stove, but I'd rather drill the rear wall (plain and out of sight) than the side walls (which have a cast-in patterns, and look really nice on the Jotul).

I aim to have the main part of my secondary air tube, the two-foot-wide part that runs east-west, wind up a just under the baffle and a few inches back from the baffle's front edge. I would be interested in any discussion of the optimum place to inject secondary air in a baffled firebox... I'm just going by what I've seen and used in other EPA stoves.

My big question concerns the number and size and orientation of the holes in the secondary tube. All I can say so far is that I plan to start with a few small (1/16") ones aimed down about 45 degrees, and add them and enlarge them as I see how the burn looks. So I would also be interested in any discussion regarding the optimum size and total area for secondary air injection... and what the tradeoffs are in terms of what happens if you inject TOO MUCH secondary air.

Great discussion so far!

regards,
Eddy

pen · Dec 24, 2008

glfporsche said:
I don't want to drag us too far from Pen's mods; but to answer a few questions: My secondary air tubes are in fact 3/4 inch. The baffle is McMasterCarr part number 93595K73. It is a ceramic board made of aluminia and silica. It has the consistancy of foam, very low density and soft, but it can take 2300 degrees F, and is a very poor conductor which means it reflects heat back into the fire box. It is mounted at an angle, which I regret as it makes it harder to get the wood pushed all the way back. The baffle is about 4 inches from the inlet of the stove pipe.

To comment on Pen's conserns on adding more secondary air, and that leading to overfire. I actually believe that you can add more secondary air right at the top of the baffle and this will burn off the smoke but will not increase your temps all that much, and not increase your burn rate. The bulk of the air that's injected right at the baffle does not seem to get down to the main fire and thus does not seem to increase the burn rate.

I more than quadroupled my secondary air supply when going to the stainless tubes. I use a little less primary air now but not four times less, and the burn rate is about the same. Actually, I find it harder to overfire now.

I've updated with some flame picts: http://glfporsche.smugmug.com/gallery/6450885_NdHjA

If you look closely, the picts at the bottom are with the stainless tubes and much increased secondary air. You can see a contionus ribbon of flame coming off the rear most tube. The secondary air enters the at the passage welded (poorly) to the side of the stove.

Kris

Great pics. If I understand you correctly, do you think a secondary tube above the baffle (as in the upper chamber of the stove) would be effective?

If so, that would be wonderful as it would definitely not affect the size of my firebox. I had counted this idea out because I didn't think it would be hot enough here? Or that the secondaries needed to be directly into the flame? I was afraid that a secondary in this area would mainly work to dilute to gasses but wouldn't be effective for creating combustion.

pen

pen · Dec 24, 2008

Peter B. said:
pen wrote:

>While I love the added heat gained from my wood, what I am not happy with
>is my flue gases. I now have smoke I never did before except for
>about 10 minutes after a reload. From then on out, it would be nothing
>but heat waves. Now, I am getting 30mins on an average load to 60-75
>minutes on an overnight load of white smoke from the chimney. All the
>while the stove is producing killer heat and the chimney is about 350
>degrees (normal).

...and...

>I have discussed the smoking issue with the metal shop buddy who built
>this for me, and he believes even with the added smoking that I am going
>to find less 2nd degree creosote in the chimney since I am no longer
>needing to use my stove damper and the velocity of my flue gasses will
>have increased.
>
>Even if he is correct, the smoking issue bothers me from a smell
>standpoint (I like my neighbors) and an environmental standpoint (no tree
>hugger but I don’t like making a bigger impact than necessary).
>
>My thought is that a simple secondary, while it may not be perfect, may
>add enough extra air in the back of this baffle to help better burn this
>smoke I am finding.

--

You've likely read this here before, but most people say white smoke that dissipates to the surrounding air quickly is likely (mainly) steam from the moisture in the wood. If it's dark and lingers (and has any odor to speak of), that's 'real' smoke.

Again, I'm far from expert, but I'm inclined to think that yes, the secondary _should_ help burn off the 'added' smoke.

Also, I might continue to use the flue damper judiciously. You don't really want a rapid velocity out of the stove proper... but rather a semi controlled 'reside time' within the stove to help mix volatiles, heat and air for complete combustion... before the exhaust enters the flue.

Peter B.

-----

I now agree that it was mostly steam as a result of the ambient air. (I noticed that when the furnace fired up to heat hot water while I was watching the wood stove chimney that it too had the same steam) Essentially, duh

Just me being over paranoid! However, the idea of including a secondary is still interesting and has created great conversation.

I would like to thank everyone for their open and most importantly intelligent conversation regarding this topic. On many forums, that is tough to come by!

I think this shows that wood burners are inherently a different and perhaps even superior breed!

pen

jacksnipe · Dec 24, 2008

I'm trying to grasp ahold of all this info but am getting a bit confused about the secondary tubes etc. located above the baffle. Doesn't make much sense to me with it being located there, most of the mfg have it located under the baflle. I also wonder about the clearance issues between the baffle
top surface & the appliance flue oulet, is there a engineering spec in place for this fiqure. I saw that 4" was given on the design with the pictures of the wonderful secondary in operation, could this dimension be reduced to 2" to increase the usable fire box height. I'm also a bit reluctant to start drilling the firebox.

pen · Dec 24, 2008

I decided to make my baffle as tall as it is based upon the area of my 8 in flue pipe. The opening left from the top lip of the baffle to to the bottom of that front plate leaves the same to a little more surface area as the flue so that I wouldn't have a issue smoking. So far so good. When I open the door, there is no smoke issue at all that comes into the house.

This height also ended up so that the bottom of the baffle is approximately 1 1/2 inches above the top lip for the door. You can't load the stove any higher than the door will allow when loading front to back, so this has not restricted the amount of wood that I put in the stove. Although it has reduced the amount of wood that I need to put into the stove.

Now, I made my baffle overlap the front lower area of my stove top by about a 1/2 an inch. It sounds like the other person with a baffle brought it a bit closer to the front of the stove if I understand them correctly.

pen

Malatesta · Dec 24, 2008

Excellent job on the secondary tubes , And nice baffle Pen I have Grandma bear fisher to 1980 it has a baffle in it already. Kinda only a half baffle thou. The secondary tubes are a great idea. These old stoves are pretty indestructible. I was thinkng of running secondary tubes in mine . Same kinda set-up only running the air supply towards the back and Then down the back of the stove. Then maybe the air supply out the bottom.

jacksnipe · Dec 24, 2008

pen said:
I decided to make my baffle as tall as it is based upon the area of my 8 in flue pipe. The opening left from the top lip of the baffle to to the bottom of that front plate leaves the same to a little more surface area as the flue so that I wouldn't have a issue smoking. So far so good. When I open the door, there is no smoke issue at all that comes into the house.

This height also ended up so that the bottom of the baffle is approximately 1 1/2 inches above the top lip for the door. You can't load the stove any higher than the door will allow when loading front to back, so this has not restricted the amount of wood that I put in the stove. Although it has reduced the amount of wood that I need to put into the stove.

Now, I made my baffle overlap the front lower area of my stove top by about a 1/2 an inch. It sounds like the other person with a baffle brought it a bit closer to the front of the stove if I understand them correctly.

Click to expand...

pen

I'm at a loss here to understand what the distance is from the door opening to the front edge of the baffle. The Fisher Insert is of a little different design, in that it incorporates a flue type baffle plate that drops down when open so the top of the baffle will have to be probably 1 1/2" lower than this so it won't hit. I too like to run with the doors open on occasion to view the fire so I don't want it set off the smoke alarms.
As of this point I have the tube materials in seamless 1" dia. 316 sst. & the manifold material, I have been on the McMaster Carr website looking at the baffle material which can be cut size the stove as needed. I haven't got the nerve yet to drill a hole in a perfectly good stove to install the secondary air supply.

Bigg_Redd · Dec 24, 2008

pen said:
Yamaha_gurl said:

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

Click to expand...

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

My parents have a Kodiak made Fisher knock off insert with a baffle.

kksalm · Dec 24, 2008

This is a wonderful thread. What I've been wanting to do is convert my fireplace into something like glfporsche's wood stove. All I need is a good airtight stove door with an accompanying framework to seal the front of my fireplace. I would make a suspended baffle complete with the hanging secondary burn tubes out of steel and incorporate high tech fire brick to complete the stove rather than build the rest with steel. More or less a masonry stove using the principles being described in this thread. My fireplace has ample room to build a masonry stove inside of it and contains lots of mass to retain the heat. Thanks all for an inspiring thread.
Best regards, kksalm

pen · Dec 24, 2008

jacksnipe said:
pen said:

I decided to make my baffle as tall as it is based upon the area of my 8 in flue pipe. The opening left from the top lip of the baffle to to the bottom of that front plate leaves the same to a little more surface area as the flue so that I wouldn't have a issue smoking. So far so good. When I open the door, there is no smoke issue at all that comes into the house.

This height also ended up so that the bottom of the baffle is approximately 1 1/2 inches above the top lip for the door. You can't load the stove any higher than the door will allow when loading front to back, so this has not restricted the amount of wood that I put in the stove. Although it has reduced the amount of wood that I need to put into the stove.

Now, I made my baffle overlap the front lower area of my stove top by about a 1/2 an inch. It sounds like the other person with a baffle brought it a bit closer to the front of the stove if I understand them correctly.

Click to expand...

pen

Click to expand...

I'm at a loss here to understand what the distance is from the door opening to the front edge of the baffle. The Fisher Insert is of a little different design, in that it incorporates a flue type baffle plate that drops down when open so the top of the baffle will have to be probably 1 1/2" lower than this so it won't hit. I too like to run with the doors open on occasion to view the fire so I don't want it set off the smoke alarms.
As of this point I have the tube materials in seamless 1" dia. 316 sst. & the manifold material, I have been on the McMaster Carr website looking at the baffle material which can be cut size the stove as needed. I haven't got the nerve yet to drill a hole in a perfectly good stove to install the secondary air supply.

Stove is burning and I am not going to stick the measuring tape in there now. I didn't worry about the distance from the door but rather just a 1/2 in overlap of the front lower top plate of the stove.

Maybe this will help

pen

WES999 · Dec 24, 2008

A few thoughts on baffles. When I was designing the modifications for my Fisher stove, one of the first things I did was to study as many of the online stove manuals I could find, look at the Englander NC-30 manual, it shows the size,number and orientation of the air holes. Note how the holes in the rear ( closest to the air supply are smaller than the holes in front) to balance the flow. The baffle design in the Englander seems to be the most common and wildly used. I have attached some drawings of my stove so you can see how I made my baffle and secondary air tubes.

bokehman · Dec 24, 2008

Pen, your secondary air needs to be injected below the baffle. That is the hottest point. Above the baffle won't be efficient.

Regarding whether or not the secondaries are necessary the answer is they are. If you look at the photos of the Lopi modification there is flame at the secondaries. If they weren't necessary there would not be flame there.

Malatesta · Dec 24, 2008

Wes how do the secondary air tubes get there air supply ? I tried to max out the pics it was tuff to see.

jacksnipe · Dec 24, 2008

Pen: Thanks for the drawing that shows the baffle outline. I can see why it doesn't smoke much, In your original photograph of the baffle assy. it looked much closer to the door opening. I forgot about the 2 step design of the stove where the front half is lower, the insert model has a flat top all the way from the front to the rear. So I'm guessing here that the set back for the front of the baffle would be about the width of 2- 3 of the vertical side firebricks = about 9" - 12" from the door opening. The rest of the measurements you noted would follow in line to utilize the baffle in the insert.
Note: The firebox size for the insert is 18" wide x 26" deep, the front edge of flue opening with the damper plate is 18" from the door opening. I'm seeing other designs also that show this baffle unit mounted at a slight angle, I'm curious if this is necessary

pen · Dec 24, 2008

bokehman said:
Pen, your secondary air needs to be injected below the baffle. That is the hottest point. Above the baffle won't be efficient.

Regarding whether or not the secondaries are necessary the answer is they are. If you look at the photos of the Lopi modification there is flame at the secondaries. If they weren't necessary there would not be flame there.

Good point.

That is what I was assuming but wanted to double check after reading the comments of the one individual.

As far as the true necessity what I really should have said is "will it be worth my while." There is no doubt that they will improve efficiency but with my setup and means, I am just trying to figure how much more I would truly gain and if it would be worth the effort. Considering the heat gain I am seeing and the less wood I am using, the only other concern for me is chimney cleanliness. If my chimney is not as clean or cleaner than it usually is after one month, then I will take the next step. Otherwise, I am not sure if the risk involved with modification plus diminishing the size of the usable firebox would be worth it.

pen

pen · Dec 24, 2008

jacksnipe said:
Pen: Thanks for the drawing that shows the baffle outline. I can see why it doesn't smoke much, In your original photograph of the baffle assy. it looked much closer to the door opening. I forgot about the 2 step design of the stove where the front half is lower, the insert model has a flat top all the way from the front to the rear. So I'm guessing here that the set back for the front of the baffle would be about the width of 2- 3 of the vertical side firebricks = about 9" - 12" from the door opening. The rest of the measurements you noted would follow in line to utilize the baffle in the insert.
Note: The firebox size for the insert is 18" wide x 26" deep, the front edge of flue opening with the damper plate is 18" from the door opening. I'm seeing other designs also that show this baffle unit mounted at a slight angle, I'm curious if this is necessary

]

The dimensions of my baffle are 22 wide and 12 inches deep. The height is 5 1/4 to the bottom of the firebrick in the baffle from the top of the firebrick in my box. This makes for 6 1/2 total height above the firebrick. I couldn't make my baffle any deeper than 12 inches because of the table design that I made. If I made it deeper, the metal angle iron firebrick retainers on the sides of the stove would have been in the way.

I think that the sloping feature of the other baffles were due to the rear exit whereas my stove is a top exit flue.

At least one individual who posted here mentioned that they wish they had not sloped their baffle.

pen

BJ64 · Dec 24, 2008

This is a great thread.

It makes me want to buy some of the old stoves such as a Schrader and what ever else is available and mod them like this for the shop, my buddy's shop, the brother-in-law's shop....

Anyway, great thread.

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

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