Baby Bear

[jjs777_fzr]

You asked Coaly..but here's my .02 anyways.
I made my baffle so that it would extend further to the front - so that - if I catch your question right - it extends under the low part of the stove creating a smaller area for smoke and flame to travel up and around.
I know some folks made their baffle so that it did not extend to the lower section. I thought it better to keep the smoke and fire in the stove longer and make more heat. If I totally missed your question than sorry!
I've since sold the Baby Bear - didn't like the fluttering etc it would exhibit.

 

[coaly]

Hi, and welcome to the Forum,
I aim it at the lower bend. The angle changes things as well as the open space area the smoke has to travel through. In a Baby Bear, the firebox is so small the wood is almost up to the baffle and flames touching it are quenched more than a deeper stove keeping the flames lower. That's not a problem (called flame impingement) since it makes a hotter plate, counter acting the flame quench by raising the internal temps with the plate. Flame tips lose their heat to metal quickly lowing the combustion zone temp, which is where a cleaner burn comes from, so the loss isn't that great since you have the hotter surface of the baffle now.
Another trick to get the most out of the smaller stove is to notch the baffle plate corners. This puts a stream of moving gasses towards the corners. Think of it as stagnate pockets in the corners that don't allow the gasses to contact the firebox in the corners dissipating their heat. The less square inch surface area you have, the hotter you need it. So taking advantage of every square inch raises BTU output. One of the purposes of the baffle is to slow the gasses keeping them in the stove longer, increasing the heat "soak" through the stove. So the flatter the better as far as slowing the gasses, but adding to flame impingement. Smoke space, or the square inch area the exhaust travels at baffle edge is the most important. Try to keep it near 28 square inches for a very good drafting, insulated chimney. The worse the chimney, the larger the space.
My cabin is solid log walls and currently uninsulated ceiling. I heat it (800 sf) with a Mama Bear and when the ceiling is done, I may need to go to a Baby. It's nice having a larger stove then necessary when entering a cabin below freezing - it's not the normal heat requirement things used in heat calculations. It's nice to have the larger cook surface and a nights worth of fuel load too! Solid logs lose a lot of heat, but they make up for it once heated by their mass. Unfortunately we don't get to take advantage of that when not keeping them up to temp all winter. Then it would probably be just right. Don't be afraid to oversize the stove in your case.

 

[coaly]

Hi FZR; I think the Baby Bear flutter is due to the close proximity of the intake to the out gassing fuel. I had the same thing with the 6 inch insulated flue I tried all the Fishers with. That was the only one that would flutter at the intake. Never tried placing the wood farther away from the inlet.........

Thought a lot about your question of using BTU ratings, and I think it's due to all the factors that determine surface temperature. You can calculate the output capacity by the temperature of the square inch surface area, but those numbers would not be a real world output and people would expect it to perform to those numbers not understanding the many variables involved.
Here's a pdf of a neat little slide rule type gadget for figuring BTU output using surface temperature and surface area. They were available at Woodman's, not sure if they still are. The other side is a calculator for BTU requirements in climate zones for the square heating area. As you know, with an IR, surface temps vary greatly, so an average is used constantly. (Fisher was calculated with 8 foot ceiling)