Masonry Magazine February 1983 Page. 28
with refractory units to obtain a thickness of at least 2½ in. (63 mm). The refractory units on the rear wall of the firebox should extend to the top of the first baffle, as shown in Figures 1 and 2.
The top of the firebox may be formed either by using a precast reinforced refractory concrete slab, or by using refractory units which will span the width of the firebox. Both options require slabs or units wide enough to bear at least 2 in. (50 mm) on the side walls of the firebox liner. Another alternative is to form the top of the firebox with a masonry arch constructed of refractory brick units. This method of forming the top of the firebox is compatible with using several types of Dutch oven doors for the front of the fireplace.
Vertically Baffled
The baffle system for the vertically baffled Russian-style brick masonry heater is the easiest baffle system to build. There should be at least three vertical baffle chambers and usually no more than five, although successful systems have been built with up to nine. The greater the number of baffles, the longer the masonry heater needs to be fired to warm the entire mass of brickwork. This may decrease the efficiency of the system for both heating and combustion of the wood. It will also result in much hotter fires, which may augment the deterioration of the masonry heater. Another problem with using more baffles is that those portions of the heater which remain cooler invite creosote problems.
The baffles should be formed by using a single wythe of brick masonry to separate the baffle chambers, which are usually 64 to 144 sq in. (40 000-90 000 mm²) in cross-sectional area. These single wythe brick baffles should be masonry bonded to the interior wythe of the enclosing 8-in. (200 mm) brick masonry. Thus, thermal expansion of the baffles will impose a lateral load on the enclosing brick masonry which should be considered in the design. Major cracks in the heater should be avoided by keeping the wythes of the 8-in. (200 mm) thick enclosing brick masonry walls separated by a nominal 1-in. (25 mm) air space. To help insure that thermal expansion is provided for, this space may be filled with a compressible, non-combustible material. If a filler material is used, it may be easiest to construct the interior wythe with properly spaced ties, then wrap the heater with the compressible, non-combustible material, prior to constructing the exterior wythe.
Another problem is that thermal movement may separate the baffles from the interior wythe and allow lateral movement of the baffles. Thus, in addition to the masonry bond to the interior wythe of the enclosing walls, metal ties should also be installed every 8 in. (200 mm) vertically. These metal ties should be the only metal inside the interior wythe of the enclosing walls of the brick masonry heater, except for reinforcement in concrete slabs. The top of the openings through the baffles may be formed by corbeling brick units, as shown in Figures 2 and 4. Other alternatives for forming the baffle openings are shown in Figure 5. There should be at least 12 in. (300 mm) of brick masonry covering the top of the baffle chambers. Baffles with openings at the bottom are again single-wythe brick masonry walls. The openings in the bottom of baffles may be formed by using corbeled brick masonry, brick masonry arches, or by masonry units, or reinforced, precast concrete long enough to span the width of the baffle chamber and bear a minimum of 2 in. (50 mm) on each side of the interior wythe of brick masonry. At the front face of the masonry heater, near the bottom of the baffle chamber, a clean-out door is recommended so that any ash buildup may be removed from the baffle chamber.
The last upward baffle chamber in the baffle system, i.e., the chamber at the front face of the heater, becomes the support for the conventional flue liner. By corbeling the top course of the last baffle chamber, the support for a conventional clay flue liner is obtained.
Horizontally Baffled
The baffles for the horizontally baffled Russian-style brick masonry heater may be formed by using corbeled brick masonry, arches, a pre-cast, reinforced concrete slab, or clay flue liners. When the slab is used, it should be sufficiently wide to span across the width of the baffle chamber and bear at least 2 in. (50 mm) on the interior wythe of each side wall of the baffle chamber. Arches or corbels used to form the air passageway may be started from the interior wythe of the baffle chamber wall. These are shown in Figures 3 and 5. The horizontal baffle system requires a clean-out at the bottom of each baffled area. The side and either the front or rear baffle chamber walls (depending on the number of horizontal baffles) and the top of the last baffle should be used to support the conventional flue liner for the chimney. There should be at least a 12-in. (300 mm) thickness of brick masonry forming the top of the last horizontal baffle.
Clean-Outs
Clean-outs for the baffle chamber of either Russian-style brick masonry heater are optional. Usually, when properly seasoned wood is used under adequate air intake conditions, and at high temperature, creosote should not form in large quantities. In addition, because of the baffles, most soot and ash remain in the firebox. However, the installation of clean-outs is recommended to observe any buildup. If a buildup is occurring, the operation of the stove should be modified, so that the buildup no longer occurs. This may be accomplished by increasing the amount of combustion air being supplied through the firebox doors.
Crown
The crown of the Russian-style brick masonry heater should terminate at least 12 in. (300 mm) below the ceiling of the room. Multi-story heaters are not recommended because the distance the combustion gases must flow, from the firebox through the baffles to the chimney, cools the gases and decreases performance. Typically, the distance from the firebox through the baffle chambers to the chimney should be limited to no more than 16 ft (4.9 m). The crown should be at least 12 in. (300 mm) thick, starting from the highest point of the baffle chamber. The crown may be flat, but is often constructed as an arch for esthetics.
Chimney
The chimney for the Russian-style brick masonry heater is similar to those used for fireplaces. The chimney should be constructed with clay flue liners and 8 in. (200 mm) of brick masonry surrounding the flue liner in such a way that a nominal 1-in. (25 mm) air space