Simple Baffle Solution for your old FISHER ! More Heat Less Smoke under $25

[Ski-Freak]

Several years ago I installed a baffle that I made out of an angle iron frame filled with shelf of firebricks, and it is still working great!

Fisher Firebrick Baffle in use by Ski Freak, on Flickr

 

[springer12]

This 5 minute baffle plate install is the easiest way I've found to reduce smoke and prevent intense heating of the rear outlet elbow or pipe. (20 years late, but better late than never) And possibly the best solution for anyone who can't afford to upgrade to a new stove; Approximate cost under $25.

This pertains to a rear vent, but can be altered for a top vent as well. Simply measure across the inside of your stove width. Obtain a piece of steel plate 5/16 thick from a local steel fabricator or supplier 1/2 inch shorter than this measurement. I made mine (15 long X 8 inches wide for a Mama Bear. Mine cost 1.42 / lb. weighing 11 lbs. Cost $15.62) The only other materials required are 2 firebricks available at mason supply or stove retailer. (the type that line your stove 4 1/2 X 9 X 1 1/4 thick) Papa is the same height stove for brick supports, just a little longer plate to reach across the stove.

1). Simply set the firebrick on edge against the side walls on top of the first course a couple inches from the rear wall. Upright for a Mama or Papa works great, sideways for Baby.
2). Insert the plate through the door, tilt it sideways and rotate until it is between the side walls.
Raise it to the top, and set it on top of the firebrick.
3). By sliding it rearward, you can let it tip down in the back until it's at about a 45* angle in front of the rear vent. Many rear vented stoves have a short shelf under the outlet pipe to set it on as well.
4). Make sure the opening above the plate to stove top is an acceptable size opening.
This can be adjusted by moving the bricks fore and aft to change the angle and opening if required.

The only technical measurement is the opening above the baffle plate. This must be at least as large as the square inch area of your outlet. (6 inch round formula is pi X r squared or 3.14 X 9 =28.26" square inch opening. An 8 inch Grandma or Grandpa would be 3.14 X 16 or 50.24 square inch opening) This is about 2 inches from the top, all the way across any model Fisher Stove. You can adjust it to your exact size, but I find it doesn't make much difference making the opening exact.

I found once in place, this is quite solid and doesn't want to move. It also doesn't noticeably decrease firebox size.

The intense heat that normally would heat the rear outlet elbow now goes up the plate and burns the unburned smoke particles before they get to the outlet. This also directs the heat to the stove top instead of in the direction of the exhaust. (rearward) Huge reduction in smoke. (about 90% reduction as calculated in EPA testing with and without baffle) Nothing permanent is added to the stove. This would also be the perfect area to add a secondary burn tube to admit oxygen at this hottest area.


I was going to fabricate an angle iron frame to support a baffle plate, and realized I had some old firebrick laying around that the plate could set on instead. Much cheaper than angle iron, and some single door stoves use this second course of brick above the first at the rear anyway. I positioned the new baffle plate that cost a total of $16 and 2 bricks in the stove in less than 5 minutes. I expected to need to cut the corners of the bricks on angles, but the plate sat right on the full bricks in the Mama Bear shown below. Extremely simple !

I'm a newbie here just got a Fisher Mama Bear and has a side outlet and would like to install a baffle plate, the outlet bottom is lower than the top of the front top plate of the stove. Do you just drop the plate down to the bottom of the outlet even though it would be lower than the front plate. Help would be appreciated.

 

[coaly]

The outlet pipe is usually the same height and the front edge of baffle plate should be just under the lower bend making the rear of the plate much lower than than the lower top. All of the baffle is always below the lower top plate height.
Try with a piece of cardboard as a template and put in place as if it were the steel plate. Can you set the cardboard on the brick retainers at rear and tilt upwards towards the front to get the proper smoke space for the chimney? It can be against the bottom of pipe. To start, set baffle angle (smoke space) at the same square inch area as chimney flue square inch opening. This is the minimum smoke space area you can not excede. You can then adjust for more draft (larger opening) depending on height and pipe configuration that adds resistance to flow.

 

[springer12]

Thanks coaly it looked like in the pictures on page 1 the the baffle bottom and the front top bottom were on the same plane. The bottom of my outlet is 2" below the top plate, if you were to draw a line to the outlet, but if it is fine to be below it I can handle that. Yes I all way use cardboard to make patterns out of saves a lot of good material that you would use up in trial and error. I like this place there is a world of information here about Fisher stoves. I checked my draft knobs like you said in another thread, and mine are wore out, they wobble bad. Has any one ever tried to put a helicoil in the nut as a repair?

 

[coaly]

I'm sure that would work fine. Good idea for any of the cheap knobs without the steel insert too ! I'd replace the bolt as well and keep it greased !

If you measure inside the stove from the top down to the brick retainers, then transpose that with a chalk line on the side, you can draw a line with straight edge aimed at the bottom bend and come up with the angle it will be. That will show if your side vent pipe will be in the way. Here's two pictures showing how the pipe location can differ. The farther towards the back, the better for the baffle. That's why there is no simple answer on measurements, any stove can differ slightly from "just the way it was done" at different fabricators to special made for a customer.

Both are Papa Bears.

 

[springer12]

Yep coaly the first one looks like mine, thanks for all the good information I'll make sure it don't go to waste> I will post a picture when finished. Thanks for all the help.

 

[Don H]

coaly, do you know how much a baffle adds to the efficiency of a Fisher stove?

I imagine this could be a hard question since it is a very general one with lots of possible variables but I was wondering if there was an approximate amount of increased efficiency.

 

[begreen]

Just a seat of the pants guess - Done properly maybe 10% increase in efficiency? If a secondary air supply is introduced then perhaps up to 20% increase?

My thinking is that without the baffle the stove is ~40% efficient. Adding the baffle maybe brings it up to 50% and the baffle + secondary tubes is up to maybe 60% efficient if done well. With insulating firebrick and blanket on top of the baffle maybe 65%?

 

[Don H]

Very interesting. What is the efficiency of the new stove?

 

[begreen]

Varies with the stove and combustion method but around 65-81%

 

[coaly]

I don't know, but take the baffle out of a new stove and how much does it loose?

I can tell you if you have an 8 inch flue on an 8 inch stove and add a 6 inch liner and matching smoke space area above a baffle plate, (28.26 square inches) you're going to see a huge increase in heating capacity. I've had questions from people with oversize chimneys in small cabins (900 sf) that they couldn't heat with a Baby Bear. Corrected the chimney and baffled them and they have plenty of heat. So it's a combination. A chimney that needs tons of heat isn't going to benefit from a baffle, so the chimney comes first, then fine tune the heat loss.

 

[Don H]

So if one were to take an old Fisher Papa Bear running at about 40% efficiency and add a baffle it could be brought up to 50%.
Adding secondary air and insulating the baffle with a few firebrick brings it up to 65% efficiency (all rough estimates).

So is there any reason to scrap your old Fisher for a new stove to gain maybe 10 -20% more efficiency?

I plan on adding a baffle to my Mama Bear soon but since I don't burn it much (it's my back up heat source) I probably won't notice the difference.

 

[coaly]

My issue with the new EPA stoves is the usable heat burn time. They are great to fire up, close down as soon as the top reaches secondary combustion temp, and you have a smokeless fire. Until it burns down enough to require more wood and you open them up to get the temps back up before going into another secondary burn cycle. How long that cycle is depends on the stove and how much heat you require. 3 hours when cold is what I found before reload. So the house temp drops with a glowing mass of coals compared to the older stove producing heat much longer. I don't understand how people with only wood heat keep it comfortable. My definition of comfortable is normally 68 in the morning, no lower than 66 (it will hit 64 when not cold enough to burn hard overnight, like right now) and try to stay below 72 during the day. The colder it gets the closer I can keep it. This is measured in a room farthest from the stove.

My neighbor bought a new Lopi Endeavor last winter. He has to baby sit it every 3 to 4 hours to keep his house constant. After work he has a cold house. Mornings he has a cold house. He added electric baseboards for back-up. We have the exact same house. Log cabin kit brought from Finland in 1972. He lives in his full time. Mine is a secondary home. I don't have electric, only a Mama Bear that keeps the place warm overnight and if I'm gone 10 hours during the day. He also has a blower and outside air intake. Yes, his is "more efficient" and burns less fuel. His also creates less usable heat in the cabin. I also cook on my Fisher, and heat wash water in a tub. His Lopi will not boil water and the top does not get hot enough to cook on.
His heat is IN the firebox to burn off the smoke particles. My heat is on the stove top to use. Mine is in the center room radiating in all directions. His is in a corner with a blower to distribute heat. He froze up under kitchen last year and added the extra electric baseboard for this year. I thought he was doing something wrong, showed him a moisture meter, his wood was fine...... and tried his myself. Same results. I could actually heat mine with a Baby Bear, but since I don't live in it full time, it's cold when I get there, so keep the oversize Mama there. It also gives me a larger cook top that I need.
My second issue is with wood. If I were to stack premium dry wood for a year or more, how much would be there if I'm not around for months at a time in the summer? I would need it to stay over a weekend in the winter to find someone burned it in their EPA stove ! I cut standing dead, split and season it a month before use. Burns fine and I can't tell you the number of times we have both been outside when I pointed to my stack with a very light haze that doesn't make it past my roof edge compared to his smoking away because he lost secondary combustion and he has to go play with it. I have under 3 feet of 6 inch Dura-Vent chimney above roof (it should be 3 feet min) and he has TWO sections outside with guy wires and it turned blue after one season. Looks terrible. Maybe more efficient, but you'll never convince me they are better.

 

[coaly]

I plan on adding a baffle to my Mama Bear soon but since I don't burn it much (it's my back up heat source) I probably won't notice the difference.

You will notice less smoke right away. Before it is even up to temp.
The front lower top will be hotter than the upper which is your hotter cook top now.
If you record temperature readings with a surface thermometer (IR is the best) both the stack and stove tops during a burn without and then with a baffle, you will see the stack temp drop and stove top rise. The stack temp becomes much more stable with baffle. They tend to run away without baffle. It's just like leaving the damper wide open after starting the stove when it gets roaring. Temperature spikes in the stack and the heat you need to ignite larger wood isn't in the stove. Dampen the kindling down (with damper not water ) and it will not run away. BTU output goes by temperature of each square inch of surface area. A thermometer in the house will show the difference and you'll probably feel it.

Why scrap any Fisher when they are selling for more than what they sold for new? Some like their new stoves, others would like their old one back.

 

[Don H]

coaly, thank you for your insight!

 

[begreen]

My issue with the new EPA stoves is the usable heat burn time. They are great to fire up, close down as soon as the top reaches secondary combustion temp, and you have a smokeless fire. Until it burns down enough to require more wood and you open them up to get the temps back up before going into another secondary burn cycle. How long that cycle is depends on the stove and how much heat you require. 3 hours when cold is what I found before reload. So the house temp drops with a glowing mass of coals compared to the older stove producing heat much longer. I don't understand how people with only wood heat keep it comfortable. My definition of comfortable is normally 68 in the morning, no lower than 66 (it will hit 64 when not cold enough to burn hard overnight, like right now) and try to stay below 72 during the day. The colder it gets the closer I can keep it. This is measured in a room farthest from the stove.

My neighbor bought a new Lopi Endeavor last winter. He has to baby sit it every 3 to 4 hours to keep his house constant. After work he has a cold house. Mornings he has a cold house. He added electric baseboards for back-up. We have the exact same house. Log cabin kit brought from Finland in 1972. He lives in his full time. Mine is a secondary home. I don't have electric, only a Mama Bear that keeps the place warm overnight and if I'm gone 10 hours during the day. He also has a blower and outside air intake. Yes, his is "more efficient" and burns less fuel. His also creates less usable heat in the cabin. I also cook on my Fisher, and heat wash water in a tub. His Lopi will not boil water and the top does not get hot enough to cook on.
His heat is IN the firebox to burn off the smoke particles. My heat is on the stove top to use. Mine is in the center room radiating in all directions. His is in a corner with a blower to distribute heat. He froze up under kitchen last year and added the extra electric baseboard for this year. I thought he was doing something wrong, showed him a moisture meter, his wood was fine...... and tried his myself. Same results. I could actually heat mine with a Baby Bear, but since I don't live in it full time, it's cold when I get there, so keep the oversize Mama there. It also gives me a larger cook top that I need.
My second issue is with wood. If I were to stack premium dry wood for a year or more, how much would be there if I'm not around for months at a time in the summer? I would need it to stay over a weekend in the winter to find someone burned it in their EPA stove ! I cut standing dead, split and season it a month before use. Burns fine and I can't tell you the number of times we have both been outside when I pointed to my stack with a very light haze that doesn't make it past my roof edge compared to his smoking away because he lost secondary combustion and he has to go play with it. I have under 3 feet of 6 inch Dura-Vent chimney above roof (it should be 3 feet min) and he has TWO sections outside with guy wires and it turned blue after one season. Looks terrible. Maybe more efficient, but you'll never convince me they are better.

If the stove is undersized it will need baby sitting. The scenario described with the neighbor's Endeavor is similar to what we went through with the Castine. The T6 doubled capacity and with the cast iron jacket it increased latent heat. The difference is day and night. But if the house is losing heat faster than the stove can recover it then all bets are off. There are a lot of variables besides the stove in this equation.

 

[qyota]

Great info in this thread!

I don't have a Fisher stove, but I have an older Security Chimneys BIS model 1 "insert" for lack of a better term. Apparently there was a baffle as part of original equipment...shown in this parts website: http://www.woodstoves-fireplaces.com/bis-upper-baffle/

When we bought the house, this baffle was not in the fireplace, rather a 1/4" thick steel plate was there, but was warped beyond usability. I've replaced the original (cracked, broken, abused) refractory panels with firebrick and mortar, and now I need to think about a new baffle. I'm considering an angle-iron rack with firebricks across, as it seems like the most sturdy option. The steel plate sure is simple, though. I'm just thinking there is a small benefit to the firebrick instead of steel, due to the heat capture and release properties of the brick over the steel.

I'll be working on it over the next few weeks, so I'll post up the final result here.

 

[Comarley]

Wow! This is an impressively long-running thread! Just a clarification question or two:

I have a Grandma Bear, top vent. Should the baffle's front edge be on the same plane with the stovetop's lower step, or below it? (I thought an earlier post said it should be in line with it, but another said it should be below for a side-vented stove...wasn't sure if that only applied to side vents.)

And if it should be lower than the lower step, should the baffle's edge line up vertically with the lower step's edge, or should it overlap (forcing the smoke on a more circuitous route), or stop short of it? It looks like in pictures that it stops short, but if I do that, it will not fully cover the vent opening, which I thought was critical.

Thanks for your help!

 

[coaly]

I noticed it has been over 5 years since I started the thread and I have not had anyone with a bad experience or even a marginal increase in performance! Most agree it makes a drastic improvement. It's difficult to say what works best since variables are always changing in a firebox as well as atmospheric pressure and fuel. You would have to have controlled conditions under test to compare results. The lower the plate, the more it hinders fuel load, so for those that stuff it to the top, that could be a factor.

Final adjustment depends on the chimney. The baffle is in the stove, but adjusted for chimney draw. If you have an insulated flue you can lean towards closing it off more. A larger flue with no insulated liner requires more heat, so you can't always make the baffle the most efficient. The space smoke travels through should be no smaller than square inch area of flue diameter, so that changes where the baffle edge ends up too.
The side vent has to be lower if the vent is closer to the front of the stove since the baffle will be up against the bottom of vent pipe and can't be raised any more.

 

[Timxhr877]

Any chance you could sketch out what this looks like in profile? I'm afraid of blocking the flue too much to meet the angle and height from the inside-top of the stove.

I believe my stove is a Momma Bear -- that's what I was told -- but my measurements seem much different from yours. Inside width (minus a half inch) is 16.5-in. The 6-in flue is not flush with the inside rear wall, but protrudes 2.75-in inside the firebox. For me to set a 5/16-in steel plate inside at 45-degrees and 2-in from the inside-top of the stove, it would need to be about 10.5-in wide.

You used a 15 x 8 x 5/16 plate but I think that would be too small for my stove. Am I missing something?

 

[coaly]

The flue pipe should protrude inside about 3 inches as you describe. Does it have a small plate like a shelf just below it? If so, you can set the baffle on that plate to hold it higher in the back and aim it towards the lower bend. If no plate, it needs to set on the rear brick support which makes the back lower and 10 1/2 would be more the depth you need to reach the lower bend or just ahead of it. Make yourself a cardboard template since the inside can be a little different from every fabricator.

The exterior of a Mama Bear is normally 16 inches wide making it 15 1/2 inside. Papa should be 18 outside and 17 1/2 inside. The log length that fits inside front to back is a better judge of what you may have. There is no way you're closing the door of a Mama Bear with a 30 inch long log straight in, front to back.

 

[Fishing-addict]

I don't know what you have. But I've been running the baffle that coaly talks about in my baby bear for a month now and I guarantee you I'll never run another one without it. You'll notice differences immediately.

 

[Piney]

Every year my baffle made of too light materials comes out, gets beaten, rewelded and put back in in time for 7-8 months of continual burning.
It's that time again. Been lighting a fire every morning for 10 days now. Soon I won't be able to let the fire go out until sometime in April.

 

[Piney]

 

[Johnny iuzzini]

View attachment 256577

You have the angle iron going longwise, did you do that to help with the warping?