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Flue and Chimney:
The flue tile should be 1 inch thick unglazed 8 x 8 inch square outside dimension
or 8 inch unglazed round tile. Caution: Do not use glazed tile, it may crack from
heat. Use high temperature mortar between flue tile joints. Because of the low
temperature of the exit gas we suggest perlite or zonolite insulation in the air space between the flue tile and the brick chimney structure to retain heat in the chimney.
Caution: do not overly compress the insulation. When capping off do not seal the
cap to the tile (allowing for vertical expansion). Do not use concrete blocks for
the chimney as they often soak up rain and may cause future chimney problems.
Chimney top covers are not necessary except for extreme downdraft problems and
to discourage birds and animals from nesting in the opening.
The heat baffles, in reality, are part of the flue (chimney) system. The horizontal baffles are separated from each other by bricks set on edge. The free flow passage of these flue (baffle) runs must be equal to, and preferably greater then the free flow passage of the flue tile. As an example, a seven inch (inside measure) flue
has 49 square inches of free flow. This requires that a baffle run should have not less than 49 square inches of area after allowing for the space occupied by the supporting separator bricks. Also, as a rule of thumb, horizontal flue runs (baffles) should not be less than 27 inches long.
Avoid Downdrafts:
Downdraft problems are best corrected by increasing chimney height or by pruning the tops of interfering tall trees. If all else fails, use a directional rotating type flue top cover to correct the downdraft. The flue top should be two feet taller than any roof surface that is closer than ten feet horizontal distance. It is best if the top of the flue is two feet taller than the gable peak. This avoids downdraft in most situations.
Damper:
The unit described here is designed for complete air control, therefore a damper is not necessary. A chimney damper should be installed if air control is not complete. However, we know of some units that operate satisfactorily without dampers or air control valves but this will greatly reduce the efficiency of the fireplace.
Construction Time:
Based on a workshop situation with no bricklaying experience, it will require about 7 to 8 working days to construct a masonry stove with hand mixing of mortar and using textured (striated) face brick for safety walls.
Others have indicated five working days for construction is adequate. Experienced bricklayers may construct a unit in a shorter period. The walls must be plumb and cross-leveled at each brick course. Pre-mixed mortars and a perfectly leveled pad will reduce the construction time. The stove constructed in a Missouri workshop
did not have an oven. The oven, as shown in this publication, and the extra arch will add to the time required (perhaps a few hours). The oven may be eliminated from this suggested design. Extra horizontal flue runs could be substituted for the oven if the oven is eliminated, or three vertical flue runs could be used. The oven is designed to aid in heat transfer to the room, reducing the normal 4 to 6 hour delay for the stove to begin adding heat to the room.
Doors and Cleanouts:
Doors should be preselected to fit your taste and the size of stove you wish to construct. The firebox door should be cast iron or insulated '/4 inch thick mild steel to avoid warping. Glass doors have been used successfully where the stove is not over-fired. There is one report of overfiring melting the glass door. Doors
can be obtained through stove dealers, iron casting foundries, from used stoves or from a few specialty companies that manufacture custom designed doors or stove parts. Some welding shops should be able to make suitable doors.
Caution: do not start brick work until the door and clean-outs are in your possession.
Cleanout doors can be standard fireplace cleanouts except at the primary flue exit from the firebox. A cleanout is not necessary in the primary flue. Cleanouts, round or square, can be purchased from local sources or made up by sheet metal shops as desired. Select cleanouts as small as practical. The use of smaller cleanouts will
often permit avoiding the use of a reinforcing angle iron lintel. Four and one-half inch brick spans can be tolerated in most situations without reinforcing lintels. Consider the weight of the chimney placement in relation to the flue cleanouts when deciding if a steel lintel is required.
Caution: In the design shown in this publication, with a front cleanout and the chimney resting on the front wall(s) a lintel is required, especially on the top run
of a three run horizontal flue design.
The vertical leg of the angle iron lintel should be on the outside of the firebrick wall and on the inside of the safety wall. If a steel frame is considered to be desirable, as a personal choice, as decor in the ornamental brick, an angle iron picture style frame can be fabricated. The drawing included is a suggested size. Fabricate the frame to fit the chosen size of the cleanout. Do not use a welded
frame in the firebrick wall because of potential cracking that may result from the heat expansion of the metal frame. Use only a lintel on the firebrick wall and allow one-fourth inch of expansion space on both ends.
The lintel should rest on at least one-half of a brick length on either side of the opening (extend 4% inches past the opening). Remove all metal burrs and rough edges, allow the metal lintel to slide with heat expansion and do not use glue or mortar on the lintel. Use some non-sticking surface separators, such as a sandwich wrap or wax paper (both melt out), to avoid binding the brick to the metal.
Sealing the Cleanouts:
To avoid smoke leaks, the cleanout must fit tight. One method of accomplishing a tight fit is to apply a thin layer of high temperature mortar cement to a dust free surface on the firebricks. Allow the mortar to become slightly firm, then slide the prefitted cleanout box into the opening and into the mortar as far as it will travel.
Immediately remove the cleanout box, wipe it clean and allow the mortar to set for 24 hours Gefore reinserting the metal cleanout box. This mortar sealing technique should be used in addition to a soft gasket in the expansion space between the walls.
Size of Unit:
The masonry stove, as described in this publication, with a firebox exterior of 27 x 36 inches, is large enough to adequately heat a 1200 to 1500 square foot residence, when insulated to R30 ceilings, R20 walls and R13 floors. This also assumes good weatherstripping, joint caulking and double glazed windows. Heat distribution by directional fans or duct work will be required to adequately disperse the heat that this stove is capable of producing. Twenty pounds of air dry wood burned in a masonry stove will deliver approximately a net value of 112,000 BTU.
With the use of special sized firebrick or castable clay a vertical flue run masonry stove could be constructed with an outside ornamental wall dimension of 25" x 25" x 6 feet high. Allowing for safety spacing with a heat shield the masonry stove would occupy a space of approximately 39 x 39 inches. This is very similar to the space required for a large radiant heat style stove. The weight of the unit would also be greatly reduced. The cost factor is uncertain as fewer but more costly materials are required, also molds are required to form the castable clay.
Placement of Unit:
To achieve its full effectiveness, the masonry stove should be placed entirely within the building envelope, only the air tubes and chimney should extend through the walls or ceilings. A masonry stove produces mostly radiant heat (similar to the sun on a clear day). Therefore, line of sight heating is the most obvious use of these units. The more open the structure and the more centrally located, the better the results.
Maintaining the Air Space:
Do not allow excessive mortar to drop into and accumulate in the air space during construction. Temporarily use boards or rags loosely fitted into the air space to avoid mortar spilling into the space. If mortar does drop into the space, use a long rod or other tool for clean-up. This air space must be maintained for free expansion or the outside wall may crack.
Gaskets:
Doors and clean-outs should be sealed with fiberglass or other soft, non-asbestos, non-combustible materials to reduce leakage of combustion gases. Stove dealers often sell gasket kits. Do not overly compress the gaskets as heat expansion may occur. Rock wool insulation will work as a gasket material around doors and cleanouts, in the air space between the two walls. WARNING: do not use fiber glass from residential fiber glass batts or blankets for gaskets, binding material will break down from the firebox heat.
Flue and Chimney:
The flue tile should be 1 inch thick unglazed 8 x 8 inch square outside dimension
or 8 inch unglazed round tile. Caution: Do not use glazed tile, it may crack from
heat. Use high temperature mortar between flue tile joints. Because of the low
temperature of the exit gas we suggest perlite or zonolite insulation in the air space between the flue tile and the brick chimney structure to retain heat in the chimney.
Caution: do not overly compress the insulation. When capping off do not seal the
cap to the tile (allowing for vertical expansion). Do not use concrete blocks for
the chimney as they often soak up rain and may cause future chimney problems.
Chimney top covers are not necessary except for extreme downdraft problems and
to discourage birds and animals from nesting in the opening.
The heat baffles, in reality, are part of the flue (chimney) system. The horizontal baffles are separated from each other by bricks set on edge. The free flow passage of these flue (baffle) runs must be equal to, and preferably greater then the free flow passage of the flue tile. As an example, a seven inch (inside measure) flue
has 49 square inches of free flow. This requires that a baffle run should have not less than 49 square inches of area after allowing for the space occupied by the supporting separator bricks. Also, as a rule of thumb, horizontal flue runs (baffles) should not be less than 27 inches long.
Avoid Downdrafts:
Downdraft problems are best corrected by increasing chimney height or by pruning the tops of interfering tall trees. If all else fails, use a directional rotating type flue top cover to correct the downdraft. The flue top should be two feet taller than any roof surface that is closer than ten feet horizontal distance. It is best if the top of the flue is two feet taller than the gable peak. This avoids downdraft in most situations.
Damper:
The unit described here is designed for complete air control, therefore a damper is not necessary. A chimney damper should be installed if air control is not complete. However, we know of some units that operate satisfactorily without dampers or air control valves but this will greatly reduce the efficiency of the fireplace.
Construction Time:
Based on a workshop situation with no bricklaying experience, it will require about 7 to 8 working days to construct a masonry stove with hand mixing of mortar and using textured (striated) face brick for safety walls.
Others have indicated five working days for construction is adequate. Experienced bricklayers may construct a unit in a shorter period. The walls must be plumb and cross-leveled at each brick course. Pre-mixed mortars and a perfectly leveled pad will reduce the construction time. The stove constructed in a Missouri workshop
did not have an oven. The oven, as shown in this publication, and the extra arch will add to the time required (perhaps a few hours). The oven may be eliminated from this suggested design. Extra horizontal flue runs could be substituted for the oven if the oven is eliminated, or three vertical flue runs could be used. The oven is designed to aid in heat transfer to the room, reducing the normal 4 to 6 hour delay for the stove to begin adding heat to the room.
Doors and Cleanouts:
Doors should be preselected to fit your taste and the size of stove you wish to construct. The firebox door should be cast iron or insulated '/4 inch thick mild steel to avoid warping. Glass doors have been used successfully where the stove is not over-fired. There is one report of overfiring melting the glass door. Doors
can be obtained through stove dealers, iron casting foundries, from used stoves or from a few specialty companies that manufacture custom designed doors or stove parts. Some welding shops should be able to make suitable doors.
Caution: do not start brick work until the door and clean-outs are in your possession.
Cleanout doors can be standard fireplace cleanouts except at the primary flue exit from the firebox. A cleanout is not necessary in the primary flue. Cleanouts, round or square, can be purchased from local sources or made up by sheet metal shops as desired. Select cleanouts as small as practical. The use of smaller cleanouts will
often permit avoiding the use of a reinforcing angle iron lintel. Four and one-half inch brick spans can be tolerated in most situations without reinforcing lintels. Consider the weight of the chimney placement in relation to the flue cleanouts when deciding if a steel lintel is required.
Caution: In the design shown in this publication, with a front cleanout and the chimney resting on the front wall(s) a lintel is required, especially on the top run
of a three run horizontal flue design.
The vertical leg of the angle iron lintel should be on the outside of the firebrick wall and on the inside of the safety wall. If a steel frame is considered to be desirable, as a personal choice, as decor in the ornamental brick, an angle iron picture style frame can be fabricated. The drawing included is a suggested size. Fabricate the frame to fit the chosen size of the cleanout. Do not use a welded
frame in the firebrick wall because of potential cracking that may result from the heat expansion of the metal frame. Use only a lintel on the firebrick wall and allow one-fourth inch of expansion space on both ends.
The lintel should rest on at least one-half of a brick length on either side of the opening (extend 4% inches past the opening). Remove all metal burrs and rough edges, allow the metal lintel to slide with heat expansion and do not use glue or mortar on the lintel. Use some non-sticking surface separators, such as a sandwich wrap or wax paper (both melt out), to avoid binding the brick to the metal.
Sealing the Cleanouts:
To avoid smoke leaks, the cleanout must fit tight. One method of accomplishing a tight fit is to apply a thin layer of high temperature mortar cement to a dust free surface on the firebricks. Allow the mortar to become slightly firm, then slide the prefitted cleanout box into the opening and into the mortar as far as it will travel.
Immediately remove the cleanout box, wipe it clean and allow the mortar to set for 24 hours Gefore reinserting the metal cleanout box. This mortar sealing technique should be used in addition to a soft gasket in the expansion space between the walls.
Size of Unit:
The masonry stove, as described in this publication, with a firebox exterior of 27 x 36 inches, is large enough to adequately heat a 1200 to 1500 square foot residence, when insulated to R30 ceilings, R20 walls and R13 floors. This also assumes good weatherstripping, joint caulking and double glazed windows. Heat distribution by directional fans or duct work will be required to adequately disperse the heat that this stove is capable of producing. Twenty pounds of air dry wood burned in a masonry stove will deliver approximately a net value of 112,000 BTU.
With the use of special sized firebrick or castable clay a vertical flue run masonry stove could be constructed with an outside ornamental wall dimension of 25" x 25" x 6 feet high. Allowing for safety spacing with a heat shield the masonry stove would occupy a space of approximately 39 x 39 inches. This is very similar to the space required for a large radiant heat style stove. The weight of the unit would also be greatly reduced. The cost factor is uncertain as fewer but more costly materials are required, also molds are required to form the castable clay.
Placement of Unit:
To achieve its full effectiveness, the masonry stove should be placed entirely within the building envelope, only the air tubes and chimney should extend through the walls or ceilings. A masonry stove produces mostly radiant heat (similar to the sun on a clear day). Therefore, line of sight heating is the most obvious use of these units. The more open the structure and the more centrally located, the better the results.
Maintaining the Air Space:
Do not allow excessive mortar to drop into and accumulate in the air space during construction. Temporarily use boards or rags loosely fitted into the air space to avoid mortar spilling into the space. If mortar does drop into the space, use a long rod or other tool for clean-up. This air space must be maintained for free expansion or the outside wall may crack.
Gaskets:
Doors and clean-outs should be sealed with fiberglass or other soft, non-asbestos, non-combustible materials to reduce leakage of combustion gases. Stove dealers often sell gasket kits. Do not overly compress the gaskets as heat expansion may occur. Rock wool insulation will work as a gasket material around doors and cleanouts, in the air space between the two walls. WARNING: do not use fiber glass from residential fiber glass batts or blankets for gaskets, binding material will break down from the firebox heat.
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ReplyDeleteIt was a great post on Masonry Mortar Manufacturers in which the manufacturer add the mortar for safely wall and it perfectly reduce the construction time.This technique is used in addition to the soft gasket in expansion between the wall..
ReplyDelete