Masonry Magazine February 1983 Page. 32
is maintained between the flue liner and the surrounding brick masonry. The 8-in. (200 mm) chimney wall is recommended to help keep the chimney at a higher temperature to increase performance. Additional information on chimney design and construction is provided in Technical Notes 19B Revised.
The chimney height required for draft is usually higher than that necessary for conventional fireplaces, but following the building code requirements for fire safety will usually result in a sufficiently high chimney. Most codes require that the chimney terminate at least 3 ft (1 m) above the roof at the highest point of exit and at least 2 ft (600 mm) above any portion of the building or any adjacent structure within 10 ft (3 m) of the chimney. If the draft is determined to be inadequate by a smoke test, the chimney height should be increased to provide adequate draft.
The chimney for the Russian-style masonry heater must be free to move vertically to allow for the vertical thermal expansion of the masonry heater supporting it. This requires properly sealed flashing and counter-flashing where the chimney penetrates the roof line.
Esthetics
An additional consideration in the design of a brick masonry heater is the esthetics. Figures 1 through 4 show the basic heater design for function. This results in a rectangular mass of brick within the building, which may or may not be esthetically pleasing. Incorporating arches, corbels, racks and mantels into the design may greatly increase the esthetic value.
SELECTION OF MATERIALS
# General
The design and construction of a brick masonry heater using products available in the United States is slightly different than the construction of the heater in Europe. European heaters are usually constructed using a single wythe of 5-in. (125 mm) thick brick for the exterior shell. The exterior brick is then often covered with glazed ceramic tiles, set in high temperature-resistant epoxy grout. Using a single wythe around the firebox and baffles may result in cracking. The positive draft through the firebox and baffle chambers results in little danger of toxic gases escaping into the occupied areas of the building. By using multiple wythes for the exterior shell, the potential for a crack penetrating completely through the heater is substantially reduced. Single-wythe construction of masonry heaters is therefore not recommended.
In addition to the construction differences of the exterior shell, the accessories used in Europe are not usually available in North America. There are methods to modify the design and construction so that products readily available in North America may be used in the brick masonry heater. The options also exist to either import the accessories or to fabricate accessories similar to those used in Europe. However, these options are usually uneconomical. Additional information regarding accessories may be obtained from the cited references.
Brick
Most building codes require that solid masonry units be used for fireplace construction. Solid brick should conform to ASTM C 216 or C 62 for facing brick or building brick, respectively. Hollow brick conforming to ASTM C 652 may be used if vertical reinforcement is required.
If vertical reinforcement is to be used to provide resistance to cracking, the brick masonry heater may be constructed using a single wythe of reinforced, grouted hollow brick. Reinforced hollow brick masonry should be constructed using at least nominal 8-in. (200 mm) thick hollow brick units. The shell of the heater may also be constructed of a vertically and horizontally reinforced, fully grouted, multi-wythe brick masonry wall. The grout core should be at least 2 in. (50 mm) thick and the brick wythes must be properly tied.
When face brick or building brick is used, the walls of the heater should be at least two wythes thick, using nominal 4-in. (100 mm) or 3-in. (75 mm) thick brick. Grade SW brick should be used because of its greater durability.
Refractory brick, conforming to ASTM C 64, medium duty, should be used for the firebox. The lining for the back of the firebox should extend to the top of the first baffle chamber. These areas are exposed to the greatest amount of heat and the refractory units are more resistant to heat and thermal shock.
Salvaged or used brick should not be used because they usually will not bond well with the mortar and lack the durability necessary for satisfactory performance. The use of salvaged brick is discussed in Technical Notes 15.
Mortar and Grout
It is most convenient and economical to use only one type of mortar for the entire brick masonry heater and chimney construction. This becomes difficult when constructing a brick masonry heater because of the specific requirements of each component. The portions of the heater consisting of building, face or hollow brick should be constructed using a Type N, portland cement-lime mortar, conforming to the proportion specifications of ASTM C 270 or BIA M1-72. The same mortar should be used for the chimney brickwork except when wind loads exceed 25 psf (1.2 kPa). Where high wind loads exist, a Type S, portland cement-lime mortar should be used. It may be desirable to use high temperature-resistant mortars, such as calcium aluminate mortars, for the interior wythes and baffles of the brick masonry heater. Such mortars will increase the durability of the heater.
The firebox and all other components constructed of refractory units should be set using a fireclay mortar, conforming to ASTM C 105, medium duty. Other refractory mortars have also been successfully used, and thus any high temperature-resistant mortars that have performed well may be used. It is not within the purview of the Brick Institute of America to recommend proprietary products. The selection of the proper mortars should be determined by an experienced fireplace expert for the specific design being considered.
For reinforced brick masonry, all cores of hollow brick masonry construction and the grout space of hollow wall