When is Firebrick too thick?

[GrahamC]

I've just rebuilt an early 1900s Esse #3 Coal/Anthracite stove, however plan to use it with wood. I repaired and re-installed the (thick - maybe 3cm) firebrick, boxed it up and it's in use. HOWEVER, unlike when it was burning anthracite and blasting out a huge heat; the cast iron box with ornamental iron 'grating' over it just doesn't get much better than warm.
Can the firebrick be too thick, thus insulating the firebox and most of the heat is going up the chimney? I've been thinking of replacing the original firebrick with thinner fireboard that may allow much more of the heat to hit the cast iron exterior, thus heat the room more.
Thoughts and advice from anyone? Thanks!

 

[begreen]

It's not the firebrick. That is protecting the metal around it from burnout. Anthracite has 50% more heat per pound than wood, roughly 12,500 btus vs 8000 btus. Additionally, the air flow to the fire is wrong for wood burning. Coal fires are bottom fed air. Wood fires are not bottom fired. Using wood, if the stove has a bottom damper, close it, and only use the upper damper to supply the fire with air. There should be a flue damper too to slow the fire. Without caution, the stove will burn wood too fast and too hot. You risk overfiring the stove. A lot of old coal stoves have been ruined by improperly burning wood in them. A better fuel to burn in this would be smokeless coal ovals or similar fuel.

 

[GrahamC]

It's not the firebrick. That is protecting the metal around it from burnout. Anthracite has 50% more heat per pound than wood, roughly 12,500 btus vs 8000 btus. Additionally, the air flow to the fire is wrong for wood burning. Coal fires are bottom fed air. Wood fires are not bottom fired. Using wood, if the stove has a bottom damper, close it, and only use the upper damper to supply the fire with air. There should be a flue damper too to slow the fire. Without caution, the stove will burn wood too fast and too hot. You risk overfiring the stove. A lot of old coal stoves have been ruined by improperly burning wood in them. A better fuel to burn in this would be smokeless coal ovals or similar fuel.

Many thanks. I have put a plate over the grating to restrict the airflow so it doesn't over-fire. Even then the metal is hand hot rather than too hot to touch when it burned anthacite. Presently testing a mix of wood and ovoids which seems to be better tho not so carbon friendly. Given the dampened fire (with plate over grid) and lower btu rating, the chance of over-heating the metal is mitigated.
My 'limit case thinking' was that if the firebrick was ridiculously thick most all the heat from the fire would just go up the chimney, thus my question of getting the thickness right. I'm assuming of course that the logic is that most heat comes from the metal radiating heat. If that is the case, then a thinner fireboard that allows more heat to pass across it would improve overall heat output from the fire. Flawed logic?

 

[begreen]

The heat would destroy the metal in short order if not for the firebrick. The upper part of the firebox, that is not in direct contact with the hot coals, is where the heat exchanging occurs.