Firebrick: More = Better?

[ddddddden]

My old Sedley insert has a cavernous firebox, ~ 29 x 22 x 18". Way bigger than needed for a 2,000-sq-ft 2-story house. Firebrick, standing on end, lines the sides and back, reaching halfway up the walls and filling the center of the floor with brick lying flat. I'm thinking of buying a few six-packs of firebrick and stacking them flat instead of standing on end along the walls. I probably wouldn't go higher than they now stand, due to $, but the thickness of my brick lining would increase to 4". . .can't think of a good way to attach them flat against the walls to go higher than 9" without drilling holes in the box, unless cement would hold them. I'm also thinking of moving the floor brick to the walls and covering the floor with sand instead, also covered with a few inches of ash. Does any of this sound like a good idea? Will smaller fires burn better in a smaller box? Can something of a 'soapstone effect' be achieved by stacking lots of brick in a steel box?

 

[pen]

I'd be willing to go narrower with the firebox, but don't think I'd try adding to the depth of the base or adding firebrick above the bricks on the sides for fear of overheating another part of the stove.

In other words, I can't see harm in lining the sides with another course of firebrick, but that's it.

The firebrick being closer will help insulate a smaller fire and allow it to burn better than a small fire would in a huge firebox.

The only concern I may have would be how air enters the stove and if adding these bricks would change that dynamic in any way.

pen

 

[ddddddden]

Air enters via screw drafts low on the front corners. Firebrick lining ends a few inches back from the drafts. To clarify my previous posting, the thickness of the firebrick lining is currently 1.25" everywhere. I would remove all of the bricks, substitute 1.25" of sand for bricks on the floor, lay all the bricks flat along the rear and side walls with the long edge parallel to the wall. This would give a new lining thickness of 4.5" along all the walls, and I could stack the bricks vertically until I ran out of bricks. I think the height of the original lining was arbitrarily determined by the 9" length of a brick standing on end. The stove is circa 1980. . .although it's very well made, I dunno how much rocket science went into it. Seems to be from the beefy & simple school of design. Soo, in my fantasy, the height of the firebox would remain the same. I would The width x depth would decrease from 26.50 x 21.25" to 20 x 18".

 

[Highbeam]

What do you hope to accomplish? The stove will make the same btus once it gets to the same temperature so unless you plan to only have flash fires then you will still roast yourself out. You might save some wood if you can get more efficient smaller fires. I just don't see you getting any significant change in how the stove operates.

 

[johnn]

Soapstone has the unique ability to absorb only so much heat,,say 500 degrees regardless of how hot the fire box is,,after that it stores heat to be released after the fire burns down,,your firebrick being doubled wont have the same effect. Yours is a pre Epa stove?? Does the top plate also serve say as a baffle,so to speak? I would expect this area to become even hotter as you really stoke the fire during deep winter. Is the stove up to that? Why the sand in the bottom/

 

[littlesmokey]

I agree with posts above. You would not gain in Btu's in your house, just use some of them to heat the brick. I seen no reason you can't just build smaller fires and control the shutdown. I think the brick in your stove is there to protect the sides and bottom from overheating. What you describe as your air controls suggests a stove 20-30 years old and not one of the modern EPA stoves, right?

You are going to burn as hot as your fuel supply and combustion air allow. Controlling either is better than controlling the cubic inches.

A friend a few years back tinkered with his huge woodsman stove and as able to add a secondary burn plate above his fuel. All he did was boost his efficiency, increase the box heat and force him to add two fans, but boy did it crank out the heat with a small fire.

 

[ddddddden]

Thanks for all the replies, gentlemen. Highbeam, more efficient burning with smaller fires is exactly what I'm after. I have read that smaller stoves are better for burning smaller fires, which is what I need in a relatively small house. The pre-EPA stove here is apparently SupaSize by modern standards, so I thought reducing the volume of the firebox might be a good idea. ML, I don't think there's much of a baffle in the top of the stove. There is a plate a few inches below the the exhaust vent at the center of the top rear corner of the firebox, but that plate is only ~ 18 x 10" on a 29 x 22" ceiling...I don't know how much it may baffle, but I have seen smoke circulating down the walls when I crack the door open. Are you suggesting that the upper stove will run hotter if I stack more bricks in the lower part? It's an insert, so forced air circulates around the top & sides of the firebox. Thermostatically controlled. The flue passes through the top heat exchange area, so it gets cooled too. . .

 

[ddddddden]

. . .Sand in the bottom would simply replace the firebrick floor, giving me 17 bricks to play with, which would cost $50 to buy. The bottom of the door is ~ 4" above the floor, so I usually leave a few inches of ash covering the floor too.

 

[LLigetfa]

If you have incomplete combustion because the small fires don't run hot enough then some fuel is wasted, heat is lost, and the chimney is more prone to creosote buildup. Adding more brick can help the fire burn hotter since the brick is both a filler and an insulator, but as an insulator, some of the heat will not make its way to the outside of the firebox. I notice that when I have a buildup of ashes, that I don't get as much heat from my stove and I time the ash removal with the need for heat. I let the ashes build up when it's warmer out and I don't want it to be too hot in the house. When the mercury dips I remove more ashes to get more heat from the stove.

So, my guess is more firebrick would mean cleaner burning but more heat up the flue.

 

[ddddddden]

You would not gain in Btu's in your house, just use some of them to heat the brick...just build smaller fires and control the shutdown.

I'm not trying to change the amount of heat with the bricks, just optimize the size of the combustion chamber for burning a smaller amount of fuel & air. In my fantasy, it'd be a cozy lil' fire pit that would keep the combustion reaction happy and less sensitive to changes in atmospheric conditions. Storing BTU's in the brick would seem to be desireable too...thermal buffer to help stabilize the system between small fires, so the big steel box doesn't cool as quickly (sitting in a big stone hearth, attached to a 30' stack of external masonry, located on, of course, the north side of the house. Yeah, I also need to insulate the fire place. . .)

 

[ddddddden]

Adding more brick can help the fire burn hotter since the brick is both a filler and an insulator, but as an insulator, some of the heat will not make its way to the outside of the firebox. I notice that when I have a buildup of ashes, that I don't get as much heat from my stove and I time the ash removal with the need for heat...So, my guess is more firebrick would mean cleaner burning but more heat up the flue.

LLigetfa, that's interesting. Does your stove have firebrick on the floor? I started thinking about the brick in mine after looking at the small Englander EPA stove at Lowe's. The firebox floor + walls are ~ 90% covered with brick, but it also has a ceramic baffle board in the top that would keep the heat trapped by the brick from going up the flue. My smokebeast has no such baffle, no damper, so yeah, lots of heat up the flue. One plus may be that the flue passes through the top heat exchange area of the insert, so maybe I capture some heat.

 

[ddddddden]

A friend a few years back tinkered with his huge woodsman stove and was able to add a secondary burn plate above his fuel. All he did was boost his efficiency, increase the box heat and force him to add two fans, but boy did it crank out the heat with a small fire.

Smokey, I already have 2 blowers. If I could replicate what your buddy did, that would be kickazz! Are more details available? Did he add air injection tubes too, or just a plate?

 

[LLigetfa]

Does your stove have firebrick on the floor?

My stove has 1" thick firebrick on all 5 sides of the firebox. The sides of the stove are double-wall for the secondary preheat so in my case thicker firebrick there could theoretically reduce secondary combustion.

I put 1/4" of sand under the firebrick on the bottom of the stove which is single-wall to help conduct some of the heat from the brick to the steel and the air flowing beneath it. The top of the fire chamber has firebrick laying on top of the secondary tubes creating another smoke chamber above that. The top of the smoke chamber is single-wall and is the last chance to extract heat before it reaches the flue. I considered laying several sections of small I-beam on the outside of the top plate to increase the surface area to wick away more of the heat and transfer it to the moving air. There is however, no easy way to increase the surface area on the inside of the top where the flames lick it.

My chimney stays impeccably clean which makes me think I am wasting too much heat up the flue.

 

[pen]

Does your stove have firebrick on the floor?

My stove has 1" thick firebrick on all 5 sides of the firebox. The sides of the stove are double-wall for the secondary preheat so in my case thicker firebrick there could theoretically reduce secondary combustion.

I put 1/4" of sand under the firebrick on the bottom of the stove which is single-wall to help conduct some of the heat from the brick to the steel and the air flowing beneath it. The top of the fire chamber has firebrick laying on top of the secondary tubes creating another smoke chamber above that. The top of the smoke chamber is single-wall and is the last chance to extract heat before it reaches the flue. I considered laying several sections of small I-beam on the outside of the top plate to increase the surface area to wick away more of the heat and transfer it to the moving air. There is however, no easy way to increase the surface area on the inside of the top where the flames lick it.

My chimney stays impeccably clean which makes me think I am wasting too much heat up the flue.

Ever take a thermometer on the roof and drop it down the chimney a foot or two to measure to see what the temp of the flu gases are near the top?

Maybe you just have burns that are really that clean and you aren't wasting that much heat.

pen

 

[pen]

As to the original message, as I said before, if I had your stove I wouldn't think twice about narrowing the firebox. I don't like the idea of putting sand on the bottom tho. Just spend the couple of bux on firebrick and try it out. 3 bux is about the normal cost from what I've seen. How many would you need?


pen

 

[precaud]

more efficient burning with smaller fires is exactly what I'm after.

Adding lots of mass inside the stove will be counterproductive to what you're wanting to do. It will just lower the surface temps, resulting in less efficiency all around.

 

[littlesmokey]

A friend a few years back tinkered with his huge woodsman stove and was able to add a secondary burn plate above his fuel. All he did was boost his efficiency, increase the box heat and force him to add two fans, but boy did it crank out the heat with a small fire.

Smokey, I already have 2 blowers. If I could replicate what your buddy did, that would be kickazz! Are more details available? Did he add air injection tubes too, or just a plate?

I seem to remember only the burn plate, but it was 3/8th or 1/2 inch thick. No tubes, but he cut some ports in as I remember. When the box was going flames danced over the plate. I can't tell you if he fit it tight, or how he mounted it. It'd be 20 degrees outside, and we'd be in shirt sleeves drinking coffee warming our hands from 15 feet away.

 

[pen]

more efficient burning with smaller fires is exactly what I'm after.

Adding lots of mass inside the stove will be counterproductive to what you're wanting to do. It will just lower the surface temps, resulting in less efficiency all around.

I disagree. Compared to building a small fire in the old huge cave like he was doing, he will actually got a higher stove top temp this way because the fire will burn better w/ closer proximity to the firebrick for reflective heat encouraging the fire to burn well. It just will burn for less time, because it will actually be burning well.

If mass inside the stove hurt anything they'd be using a different material for every stove. My englander is about 85% inslulation material in the stove. Flames almost never directly lick metal. Not to mention, those "russian jelly-beans" or similar masonry fireplaces certainly don't suffer from having great mass next to high heat.

pen

 

[ddddddden]

A friend a few years back tinkered with his huge woodsman stove and was able to add a secondary burn plate above his fuel. All he did was boost his efficiency, increase the box heat and force him to add two fans, but boy did it crank out the heat with a small fire.

Smokey, are more details available? Did he add air injection tubes too, or just a plate?

I seem to remember only the burn plate, but it was 3/8th or 1/2 inch thick. No tubes, but he cut some ports in as I remember. When the box was going flames danced over the plate. I can't tell you if he fit it tight, or how he mounted it. . .

Sounds fantabulous, Smokey! Ports = holes in the plate or holes in the firebox to let air into the secondary chamber? How close was the plate to the ceiling of the firebox? Thanks!

 

[ddddddden]

. . .I don't like the idea of putting sand on the bottom. Just spend the couple of bux on firebrick and try it out. 3 bux is about the normal cost from what I've seen. How many would you need?

You worry about coals finding their way through the sand and eventually burning out the bottom of the firebox? Good point! I dunno how many bricks I need. . .depends on how high I go. I could almost equal the stock height of 7.75" (9" bricks standing on end - 1.25" of brick filling the center of the floor) with stacks of 5 bricks sitting atop the floor bricks (6 x 1.25 = 7.5") and I'd need 2 stacks, so 10 bricks per side. I have 4 bricks per side to reuse, so I'd have to buy 6 new. . .Northern Tool sells 6-packs for $15. Do you see any problem with the 1.25" of air space that this configuration would leave along the edge of the floor below the stacks?

 

[ddddddden]

. . .I may go higher than 7.5". I'm starting fantasize about a FrankenStove monster with a steel plate sitting like a shelf across the new brick sidewalls. It would extend from the back wall to within an inch or two of the front. Smoke would have to go around this baffle and then travel ~ 20" across it before exiting the vent @ center top rear of the firebox. Draft is via 2 screws @ either front bottom corner. A piece of angle iron placed over the left intake could channel air to the upper chamber above the baffle, hopefully warming the air enough to support secondary burn. The right intake would serve the lower chamber. Thoughts?