Masonry Magazine January 1984 Page. 23
comfortable interior temperatures throughout the night.
Other variations in operation, such as the number of loadings and the amount of wood used for each firing may also result in increased comfort. The operator should experiment with several operations to determine how to achieve the best performance for the various seasons.
This method of operation may be used with any properly designed and constructed brick masonry heater. Because of the variations in the design of the fountain-style heater and the modified conventional fireplace, the actual method of operation should be modified for the specific design. The contemporary-style brick masonry heater is usually operated the same as a conventional fireplace.
Fountain-Style Heater.
The fountain-style heater is shown in Figures 1 through 3. It consists of a relatively conventional fireplace firebox. The smoke chamber is rectangular and the baffle chambers for circulating the combustion are located on the sides of the smoke and combustion chambers. The baffle chambers meet under the combustion chamber where combustion gases are vented to the chimney.
The heating output of the fountain-style heater may be increased by using a specially designed air supply system from the firebox doors to the smoke chamber. Providing the smoke chamber with this additional air ignites the combustion gases in the smoke chamber. The combustion gases burn at temperatures of about 1800°F (1100°C) to 2100°F (1150°C). This method of operation, because of the higher temperatures of the circulating combustion gases, greatly increases the heating capability of the heater. This second combustion within the heater also results in a very clean and complete combustion of the wood and its by-products. This nearly complete combustion maximizes the efficiency of the wood fuel and considerably reduces any creosote buildup within the brick masonry heater and chimney.
Contemporary-Style Heater.
The contemporary-style heater, shown in Figs. 4 through 7, although much more efficient than a conventional fireplace, will not achieve the high efficiency normally obtained in the fountain-style heater. The fountain-style heater achieves efficiencies of about 80 to 95 percent and the contemporary-style heater provides a heating efficiency of about 70 to 80 percent. The contemporary-style heater is designed with a rectangular firebox with the throat located at the rear of the firebox. Combustion gases are circulated through baffle chambers within the smoke chamber and exhausted to a conventional fireplace chimney located on top of the smoke chamber. Although this type of heater does not provide as much heat, it is usually preferred because it provides the esthetic appearance similar to a conventional fireplace.
See Reference 8.
Building Code Compliance
There are no major model building code requirements which specifically address brick masonry heaters or their baffle chambers. For the most part, the building code requirements for fireplaces and chimneys are applicable to the brick masonry heater except for those requirements which address the firebox and smoke chamber dimensions. All building code requirements for chimneys and clearances for combustibles are applicable. Because the temperatures normally achieved in the brick masonry heater are much higher than those obtained in conventional fireplaces, additional consideration should be given to safety and durability.
The exterior walls of the brick masonry heater should consist of at least two wythes of brick masonry when constructed of solid units. The two wythes should be separated by a nominal 1-in. (25 mm) air space. This separation prevents any cracks from penetrating the interior wythe through the exterior wythe of the heater. Filling this 1-in. (25 mm) air space with a compressible, non-combustible material will insure that a separation is provided. The two wythes should be tied to each other with corrosion-resistant metal ties, placed 16 in. (400 mm) o.c. vertically and a maximum of 24 in. (600 mm) o.c., horizontally. The exterior wythe should contain horizontal joint reinforcement every 16 in. (400 mm) vertically to add to the integrity of the heater. The ties and joint reinforcement should not occur in the same course. These provisions should prevent problems due to thermal expansion and differential movement without affecting the overall thermal performance of the brick masonry heater.
When reinforced brick masonry construction is required, the enclosing walls or shell of the heater may be constructed of fully grouted hollow wall construction or fully grouted hollow brick units. If the fully grouted hollow wall construction is to be used, the minimum 2 in. (50 mm) grout core must be fully grouted and contain sufficient horizontal and vertical reinforcement to resist structural and thermal stresses. The two wythes must also be adequately tied together with corrosion-resistant metal ties. If grouted hollow brick masonry is used, the cores must be fully grouted and sufficiently reinforced to resist structural and thermal stresses. Horizontal joint reinforcement should have proper mortar coverage in the bed joints and the units should not be less than 8 in. (200 mm) in thickness. For additional information on reinforced brick masonry construction and hollow brick, see Technical Notes 17 and 41.
In addition to the thermal movements, the exterior surface temperatures of the brick masonry heater also need to be considered. These surface temperatures normally range between 100°F (38°C) and 130°F (54°C). Temperatures as high as 190°F (88°C) have been reported on certain styles of brick masonry heaters and are typical when fountain-style heaters are operated with gas combustion occurring in the smoke chamber.
A minimum 16-in. (400 mm) clearance is recommended between the sides and the back of the brick masonry heater and combustibles. At the floor line,