Post by phyrman on Jan 3, 2024 7:00:48 GMT -8
Hello folks, my first post but I’ve been planning my first batchrocket build for the past few months. Apologies in advance for the lengthy read. I’m hoping to get comments, criticism or recommendations of my plan before I begin my build.
The goal for my first build is focused on maximum heat storage to radiate into my shop/living area of my home. The shop is 2,000 sq ft with 14’ tall ceiling, pole barn style construction, wood pole-frame clad inside and out with steel sheeting and thin batting insulation on the walls, thick batting above the ceiling. The floor is a concrete slab on-grade. The building is tight and will retain heat fairly well. Current heating is by a wood stove at one end and an antique coal cook stove at the other. Both have 6” flues. We use the space for an extension of our small home so we have a fire going in there every day from around mid September until mid May. It’s worth noting that we are located at 8,000’ above sea level. It will not be possible to replace the current flues so I will be limited to 6” (150mm) systems on both flues to heat this area. Once I build the first batchrocket, which will replace the coal cook stove I will take lessons learned and replace the Jotul wood stove.
The general design description is as follows. A rectangular brick bell, combustion core about 16” up off of floor level, firebox door in the short side of the rectangle, a steel radiator plate embedded in the long side of the rectangle roughly centered on the wall, bypass to flue for cold fire-up. The existing 6” single-wall steel stovepipe flue is about 25’ tall from floor level and runs straight up through the ceiling and roof. The external bell dimensions are 50” deep by 33” wide x 77” tall.
Design details and questions:
Combustion Core
I have already build the 6” combustion core, consistent in almost all dimensions with the published dimensions and built in the following manner. The firebox floor is refractory splits with the secondary air intake running down the center. The floor of the riser is a single refractory plate sized to the footprint of the riser. Walls of the firebox and lower riser are full size firebrick. I have some 12” x 18” x 2” refractory plates that I am using for the roof of the firebox. Above the first 3 courses of regular firebrick, the riser is constructed of full size IFB (rated 2,600F). The port walls are full size firebrick so the thickness from front to back of port is 2.5” which is ½” larger than the published dimension. Is this dimension OK or do I need to cut the port bricks to a thinner size?
I dry stacked the core outside to test fire with a thermocouple embedded into the riser in the second to last course of brick from the top. No superwool around the riser for the test burn. Ambient temperature as well as starting brick temperature was about 40F. Brick was dry stacked for a door allowing for the primary air intake. The total burn experiment ran about 2 hours and achieved a maximum temperature of 1,490F. I played with the brick door arrangement throughout, moving the primary air intake from about centered top to bottom to about 4” up from the secondary air intake. I also played with the size of the port to see what effect this had on the burn. Being at 8,000’ I am thinking I will need more than the published 5 5/8” CSA for my primary and possibly more air for the secondary. This is one of my biggest questions and unknowns at the present time. Since it was my 1st time firing up a batchrocket I did a lot of opening and closing of the door and playing with the air intake size so I didn’t get a good feel for the effects of changing the primary intake size. I’ll run another test burn and keep the door closed more. I’m not sure that this is actually a relevant test of the air intake sizes being just the bare core and not the full system with 25’ flue. Should I wait to consider any adjustments to the air intake size until I have the system built to run further tests? This does not present any issue for the primary intake size as I can wait to fabricate the door after running some tests. It will be challenging if I need to adjust the secondary once it is built.
I will build a stand out of 1.5” x 3/16” angle iron to support the core. I plan to wrap the core in superwool including between the steel and brick. I can see in my dry stack that there are gaps in spots of about 1 to 2 mm. I have a bucket of Harbison Walker Sairset refractory cement. I’ve been cautioned about using anything to seal the core, that it will crack and fall out over time. I was thinking a very small amount of refractory cement just to fill those voids, not to act as a mortar joint. Is this advisable or just a waste of time since I’ll wrap the core with superwool?
My current design has the riser at 10x the base or 43”. I read in one of the posts that Peter indicates that it is ok to go as low as 8x and not affect performance. I just want to confirm this as I would prefer to go 8x to reduce the overall height by approximately 8”.
Bell Construction
I have a large quantity of solid red clay brick to use for the bell and more full size refractory brick for the upper section of the bell. I have a good stock of Lincoln 60 fireclay powder and construction sand for mortar (there is no clay in the soil in my area, just lots of decomposed granite).
For the roof of the bell I am planning to lay angle iron welded into a tee or tee iron if I can source it somewhere else. The closest steel supply is a several hour drive and they do not carry tee. I’ll wrap the steel with superwool and lay a blanket of superwool across the full opening then lay a layer of firebrick, another layer of superwool and a layer of red brick that I’ll mortar in. Should I mortar in the firebrick? I am aware that it is wise to not locate the steel directly above the top of the riser. Since my brick is 9” wide I can center the brick over the riser, is this enough offset for the steel or do I need to make some other accommodation to get the steel further from the gas stream?
I was originally planning a single skin bell but after further reading it appears that I would be well advised to do a double skin which will also aid in thermal storage once the mass is up to temperature. Is this correct, a single skin would not be advisable? With a double skin I was thinking I could get some visual appeal of the structure by using a Flemish Bond design where the stretcher and header bricks are alternated locking the double stack together. Question is whether I need a layer of superwool between the two layers or is it ok to make it a unified structure? In either case the design would need to be a Running Bond in the upper section with the firebrick on the inner skin. Question on this section… where do I begin the firebrick, adjacent to the top of the riser or a course or 2 below this point?
I initially calculated my bell size with a single brick skin and a 10X riser height. This gave me the target ISA of 57 sq ft. Note that I deducted the wall surface area taken up by the front of the firebox (1.5 sq ft), is this correct or just ignore the firebox face size? Assuming I do a double skin, retain my current external footprint and reduce the riser height to 8X my ISA is now reduced to 44.7 sq ft. If a double skin is recommended, is there a minimum ISA that I should target or should I stick with 57 sq ft and increase my footprint accordingly?
For my flue and bypass connections I am planning a short section of 6” stovepipe mortared into an opening in the brick connected to a 90 deg elbow at the bottom and a tee with blast gate at the top to control the bypass. The location could be anywhere along the long side of the rectangle and will be what will be the back side from what we would normally see. Can anyone provide details on the preferred height of the lower flue connection up from floor level and the location of the bypass down from the interior of the roof? Does it matter where I place the connection laterally along this wall? Would it be better to be at the opposite end from the firebox?
I have planned a radiator plate to generate some immediate heat when I am firing the system. Since the goal of this system is geared more toward thermal storage and continuous radiant heat over a 24 hour period and between burns, will the radiator plate work against me and actually cool the mass between burns? I’m thinking the plate will be 3/8” thick and approximately 28” wide and 18” high. I’m thinking to fabricate a full frame in a tee shape with the top of the tee mating to the brick with a superwool gasket all around, perhaps a few tapcon screws to secure it to the brick. The leg of the tee will serve as a the mating surface for the radiator plate secured by small bolts which will allow easy removal for an inspection/maintenance/cleaning port. I am very open to hearing thoughts/modifications on this design and if it would be better to eliminate it for any reason.
For clean-out ports I was thinking a single dedicated clean-out port low on the short wall opposite the combustion core. Should I use a tee on the flue exit instead of the elbow for flue clean out? The flue connection would be of limited value for cleaning of the bell floor since it would provide limited access based on it’s placement.
Thank you for reading this lengthy post and thanks in advance for any guidance you can provide.
Glenn
The goal for my first build is focused on maximum heat storage to radiate into my shop/living area of my home. The shop is 2,000 sq ft with 14’ tall ceiling, pole barn style construction, wood pole-frame clad inside and out with steel sheeting and thin batting insulation on the walls, thick batting above the ceiling. The floor is a concrete slab on-grade. The building is tight and will retain heat fairly well. Current heating is by a wood stove at one end and an antique coal cook stove at the other. Both have 6” flues. We use the space for an extension of our small home so we have a fire going in there every day from around mid September until mid May. It’s worth noting that we are located at 8,000’ above sea level. It will not be possible to replace the current flues so I will be limited to 6” (150mm) systems on both flues to heat this area. Once I build the first batchrocket, which will replace the coal cook stove I will take lessons learned and replace the Jotul wood stove.
The general design description is as follows. A rectangular brick bell, combustion core about 16” up off of floor level, firebox door in the short side of the rectangle, a steel radiator plate embedded in the long side of the rectangle roughly centered on the wall, bypass to flue for cold fire-up. The existing 6” single-wall steel stovepipe flue is about 25’ tall from floor level and runs straight up through the ceiling and roof. The external bell dimensions are 50” deep by 33” wide x 77” tall.
Design details and questions:
Combustion Core
I have already build the 6” combustion core, consistent in almost all dimensions with the published dimensions and built in the following manner. The firebox floor is refractory splits with the secondary air intake running down the center. The floor of the riser is a single refractory plate sized to the footprint of the riser. Walls of the firebox and lower riser are full size firebrick. I have some 12” x 18” x 2” refractory plates that I am using for the roof of the firebox. Above the first 3 courses of regular firebrick, the riser is constructed of full size IFB (rated 2,600F). The port walls are full size firebrick so the thickness from front to back of port is 2.5” which is ½” larger than the published dimension. Is this dimension OK or do I need to cut the port bricks to a thinner size?
I dry stacked the core outside to test fire with a thermocouple embedded into the riser in the second to last course of brick from the top. No superwool around the riser for the test burn. Ambient temperature as well as starting brick temperature was about 40F. Brick was dry stacked for a door allowing for the primary air intake. The total burn experiment ran about 2 hours and achieved a maximum temperature of 1,490F. I played with the brick door arrangement throughout, moving the primary air intake from about centered top to bottom to about 4” up from the secondary air intake. I also played with the size of the port to see what effect this had on the burn. Being at 8,000’ I am thinking I will need more than the published 5 5/8” CSA for my primary and possibly more air for the secondary. This is one of my biggest questions and unknowns at the present time. Since it was my 1st time firing up a batchrocket I did a lot of opening and closing of the door and playing with the air intake size so I didn’t get a good feel for the effects of changing the primary intake size. I’ll run another test burn and keep the door closed more. I’m not sure that this is actually a relevant test of the air intake sizes being just the bare core and not the full system with 25’ flue. Should I wait to consider any adjustments to the air intake size until I have the system built to run further tests? This does not present any issue for the primary intake size as I can wait to fabricate the door after running some tests. It will be challenging if I need to adjust the secondary once it is built.
I will build a stand out of 1.5” x 3/16” angle iron to support the core. I plan to wrap the core in superwool including between the steel and brick. I can see in my dry stack that there are gaps in spots of about 1 to 2 mm. I have a bucket of Harbison Walker Sairset refractory cement. I’ve been cautioned about using anything to seal the core, that it will crack and fall out over time. I was thinking a very small amount of refractory cement just to fill those voids, not to act as a mortar joint. Is this advisable or just a waste of time since I’ll wrap the core with superwool?
My current design has the riser at 10x the base or 43”. I read in one of the posts that Peter indicates that it is ok to go as low as 8x and not affect performance. I just want to confirm this as I would prefer to go 8x to reduce the overall height by approximately 8”.
Bell Construction
I have a large quantity of solid red clay brick to use for the bell and more full size refractory brick for the upper section of the bell. I have a good stock of Lincoln 60 fireclay powder and construction sand for mortar (there is no clay in the soil in my area, just lots of decomposed granite).
For the roof of the bell I am planning to lay angle iron welded into a tee or tee iron if I can source it somewhere else. The closest steel supply is a several hour drive and they do not carry tee. I’ll wrap the steel with superwool and lay a blanket of superwool across the full opening then lay a layer of firebrick, another layer of superwool and a layer of red brick that I’ll mortar in. Should I mortar in the firebrick? I am aware that it is wise to not locate the steel directly above the top of the riser. Since my brick is 9” wide I can center the brick over the riser, is this enough offset for the steel or do I need to make some other accommodation to get the steel further from the gas stream?
I was originally planning a single skin bell but after further reading it appears that I would be well advised to do a double skin which will also aid in thermal storage once the mass is up to temperature. Is this correct, a single skin would not be advisable? With a double skin I was thinking I could get some visual appeal of the structure by using a Flemish Bond design where the stretcher and header bricks are alternated locking the double stack together. Question is whether I need a layer of superwool between the two layers or is it ok to make it a unified structure? In either case the design would need to be a Running Bond in the upper section with the firebrick on the inner skin. Question on this section… where do I begin the firebrick, adjacent to the top of the riser or a course or 2 below this point?
I initially calculated my bell size with a single brick skin and a 10X riser height. This gave me the target ISA of 57 sq ft. Note that I deducted the wall surface area taken up by the front of the firebox (1.5 sq ft), is this correct or just ignore the firebox face size? Assuming I do a double skin, retain my current external footprint and reduce the riser height to 8X my ISA is now reduced to 44.7 sq ft. If a double skin is recommended, is there a minimum ISA that I should target or should I stick with 57 sq ft and increase my footprint accordingly?
For my flue and bypass connections I am planning a short section of 6” stovepipe mortared into an opening in the brick connected to a 90 deg elbow at the bottom and a tee with blast gate at the top to control the bypass. The location could be anywhere along the long side of the rectangle and will be what will be the back side from what we would normally see. Can anyone provide details on the preferred height of the lower flue connection up from floor level and the location of the bypass down from the interior of the roof? Does it matter where I place the connection laterally along this wall? Would it be better to be at the opposite end from the firebox?
I have planned a radiator plate to generate some immediate heat when I am firing the system. Since the goal of this system is geared more toward thermal storage and continuous radiant heat over a 24 hour period and between burns, will the radiator plate work against me and actually cool the mass between burns? I’m thinking the plate will be 3/8” thick and approximately 28” wide and 18” high. I’m thinking to fabricate a full frame in a tee shape with the top of the tee mating to the brick with a superwool gasket all around, perhaps a few tapcon screws to secure it to the brick. The leg of the tee will serve as a the mating surface for the radiator plate secured by small bolts which will allow easy removal for an inspection/maintenance/cleaning port. I am very open to hearing thoughts/modifications on this design and if it would be better to eliminate it for any reason.
For clean-out ports I was thinking a single dedicated clean-out port low on the short wall opposite the combustion core. Should I use a tee on the flue exit instead of the elbow for flue clean out? The flue connection would be of limited value for cleaning of the bell floor since it would provide limited access based on it’s placement.
Thank you for reading this lengthy post and thanks in advance for any guidance you can provide.
Glenn
