just wondering what size people are having good luck with when it comes to adding a baffle/smoke shelf to the inside of the fisher baby bear. Was guessing around 12.75x12 but wasn't sure.
Baffle/smoke shelf plate size for Fisher Baby Bear?
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Depends on the Baby Bear model (top, rear or side vent) and with or without upper brick course. Size it for chimney (draft) and connector pipe, elbows, cap, and screen that reduces draft. (damper is variable resistance not added in) Adjust the smoke space as required for chimney system. (space exhaust travels through)
Make a cardboard template and set in place to adjust smoke space desired for chimney. A insulated, straight up 6 inch flue will accept minimum smoke space of 28.26 square inches. A less than insulated or larger size flue with elbows, excessive connector pipe..... increases smoke space and decreases baffle size. This will give you a size close to baffle required, then adjust up and down at front to increase or decrease smoke space.
Angled upwards from rear, aim it towards lower bend in top. When you get the angle and space you want, use template to cut steel plate to size.
Make a cardboard template and set in place to adjust smoke space desired for chimney. A insulated, straight up 6 inch flue will accept minimum smoke space of 28.26 square inches. A less than insulated or larger size flue with elbows, excessive connector pipe..... increases smoke space and decreases baffle size. This will give you a size close to baffle required, then adjust up and down at front to increase or decrease smoke space.
Angled upwards from rear, aim it towards lower bend in top. When you get the angle and space you want, use template to cut steel plate to size.
It's a rear flue, has two 45 offsets and the chimney is 24 feet tall. Has a weak draft when burning a lot of wood. Has a cap on the flex liner with large openings.
Not to hijack the thread but what is the optimum angle for the baffle on a rear vent stove?
The most important is the flue diameter. It must be 6 inch round all the way up with a stove as small as yours. The liner should be insulated, but if it has a weak draft, it's probably not. Make sure any clean out door or other opening into flue is sealed well.
I measured 30* on a later factory baffle.
Sometimes it has to be where it works in the stove. Normally sitting on the small "shelf" below outlet in the single door stoves, or on top of the rear brick retainers in double doors. (unless you weld angle iron to the sides to support baffle as found on later factory stoves) Aimed at the lower bend in top dictates the angle. The longer the baffle extends toward front, the more chance of smoke roll in and the stronger the chimney draft must be.
Ok thank you very much. Was just looking for a baseline and didn't know if the angle affected how much heat was directed back at the fire.
The angle affects firebox turbulence (a good thing), velocity up stack, movement towards door, and flame impingement. (increased by lower angle towards horizontal) Impingement is flame tips touching plate giving up their heat to plate and cooling the burn zone. (same as a plate too think acting as a heat sink) The benefit still outweighs detrimental factors since overall firebox temperatures rise.
Is there any way to insulate the liner if it's already installed. There was no way to run the pipe if it had the insulation cover on it. Offsets were a pain in the rump as it was.
Ok so after installing a baffle say you get a hot spot right in the center of the stove top. What should be done. Less or more smoke space or just experiment to see what happens?? Is there any way to direct the exhaust gas to the outside edges of the stove instead of it just going through the middle? Did I explain this right? If not I can try again.
The hot spot in the center is well below limits.
Without baffle; Medium fire, average surface temperature of front lower top is 350, rear is close to 500. Problem being, this is close to exhaust exit carrying heat away with it.
With baffle (minimum smoke space to match stove outlet); 515 - 550 on lower top in front of bend. Upper top 460. This was half load, air intakes 1 turn open in a Papa Bear. I used the same 6 inch insulated Dura-Vent chimney with the other models with similar results. Only the Baby Bear fluttered and didn't burn smooth. i didn't try building the fire towards the back more as suggested since it was my only heat source and I had to use it hard until the next day when I changed it out with a Mama Bear. (1880 square feet well insulated home) That was OK for mild weather when I tested these. Mid winter with colder temps down to zero required the Papa Bear.
The factory baffle on double doors had notches cut on the ends to prevent stagnet pockets of poor circulation in the front corners and help create turbulence.
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They were 2 X 3 notches cut 3 inches in from ends, 2 inches in from front edge.
I did not cut them in the single door models I tried. I don't know how much of a difference it will make in a narrow stove. I simply fitted the already tested baffle used in Goldilocks, Teddy Bear and the Fireplace Series to improve the single door Bear Series. Double door stoves and Inserts should have the notches.
Smoke particulate went from 60 grams for every kilogram burned down to 6 grams for every kilogram burned. This was Fishers research and development numbers tested in the Series III stoves at the start of EPA regulation testing. The law was written to reduce particulate in stages, and it was enough to continue production until the final level in 1988.
Without baffle; Medium fire, average surface temperature of front lower top is 350, rear is close to 500. Problem being, this is close to exhaust exit carrying heat away with it.
With baffle (minimum smoke space to match stove outlet); 515 - 550 on lower top in front of bend. Upper top 460. This was half load, air intakes 1 turn open in a Papa Bear. I used the same 6 inch insulated Dura-Vent chimney with the other models with similar results. Only the Baby Bear fluttered and didn't burn smooth. i didn't try building the fire towards the back more as suggested since it was my only heat source and I had to use it hard until the next day when I changed it out with a Mama Bear. (1880 square feet well insulated home) That was OK for mild weather when I tested these. Mid winter with colder temps down to zero required the Papa Bear.
The factory baffle on double doors had notches cut on the ends to prevent stagnet pockets of poor circulation in the front corners and help create turbulence.
They were 2 X 3 notches cut 3 inches in from ends, 2 inches in from front edge.
I did not cut them in the single door models I tried. I don't know how much of a difference it will make in a narrow stove. I simply fitted the already tested baffle used in Goldilocks, Teddy Bear and the Fireplace Series to improve the single door Bear Series. Double door stoves and Inserts should have the notches.
Smoke particulate went from 60 grams for every kilogram burned down to 6 grams for every kilogram burned. This was Fishers research and development numbers tested in the Series III stoves at the start of EPA regulation testing. The law was written to reduce particulate in stages, and it was enough to continue production until the final level in 1988.
Coaly,
Thanks so much for the PAPA bear baffle info.
I did what you said, and man was it worth it.
I blasted my stove and painted it, and added 6 inches to the legs, now I intend on burning it another 39 years,
I bought it new and put about 5 cord of seasoned red oak through it,
It is SOOO much better and cleaner now,
Thank you and Merry Christmas
gdr
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