Yeah, I don't think you're going to find "smoke space" used anywhere since it's a term I started using for a lack of a better term for the area the exhaust travels to get out of the firebox. I made and tested baffles in all the single door Fisher Stove models that never had factory baffles. They are similar to the baffles designed by Fisher research and development in 1980 for the double door Fireplace Series. They were designed for smoke reduction as the EPA regs became stricter in stages until 1988 when the strictest particle size became effective and they had to cease production.
Normally the baffle is not a factor since the resistance it adds in the firebox is very slight compared to all other resistance in the system. The "smoke space " square inch area is critical since that is what adds resistance in the firebox. (please notch the corners as shown in the Baffle Thread in the Fisher Forum. This prevents stagnation in the corners and gives more even heating of all radiating surfaces)!
That is the very simple explanation. To give you an idea of what the actual resistance to flow is, which reduces the draft the chimney creates, there are two tables that compare
resistance coefficients of chimney components and
effective resistance coefficients of stove inlet air dampers.
Resistance coefficients of chimney components are pressure drops (due to resistance, not buoyancy) in
units of "velocity heads". It's easier to just use the numbers to get a good idea of how much resistance each component or firebox design creates. For those that want to know exactly what one of these "units" are; Mass density of the gas is d. Velocity in chimney is v. The formula to come up with 1 unit is 1/2 dv squared.
Below is
resistance coefficients of chimney components;
Round elbow 45* ......... 0.2 - 0.7
Round elbow 90*...........0.5 - 1.5
90* sharp elbow (mitered) or breeching (smoke pipe inserted into brick chimney) 1.0 - 3.0
6 inch straight pipe per foot ........0.5 - 0.8
8 inch straight pipe per foot........ 0.4 - 0.6
Spark screen ..............0.5
Stove pipe damper Open negligible
Closed.......................5 - 20 (depends on metered hole size in damper plate)
Next is
effective resistance coefficients of stove inlet air dampers;
Open door has a resistance of about 2.
(closing door has a resistance through intake of 10 - 40 Wide Open. When closed the resistance exceeds 10 times the wide open resistance. Dampers that close fully as on this stove have infinite resistance closed. (this is why the OP has no problem with door open) The air inlet resistance is what gets interesting; as chimney diameter increases, this resistance as the gasses expand and cool increases significantly.
Small stoves such as this have one inlet damper;
Pipe size in inches;...............4................5.................6...............7.................8
...............................................2 - 8.........5 - 20.........10 - 40......20 - 80.......30 - 120
All other Fisher Stoves have 2 inlet dampers so you can HALF those figures for all other Fishers.
This is why only the Baby Bear had the flutter (without baffle) on my test chimney and becomes more critical with flue diameter.
That shows how the larger chimney capable of more volume "sees" the small air intake and why it becomes more important for the right chimney diameter on smaller stoves. Maybe I preach that in the Fisher Forum a little too much.
So the smoke space being equal to the flue diameter is negligible resistance. Like a flue damper, it slows velocity. The advantages of directing the heat in the firebox forward, burning more smoke particles far outweighs slowing velocity.
This data is from a table in ASHRAE Handbook and Product Directory, 1975 Equipment Volume, table 9 in chapter 26, American Society of Heating, air-conditioning and Refrigerating Engineers, NY 1975. A copy of this table is in The Woodburners Encyclopedia which Fisher recommended in the back of all manuals for further reading. It's the best book on wood burning in my opinion.
