Masonry Magazine February 1983 Page. 24
Brick Masonry Heaters
During the coldest months in severe climates such as those of Scandinavia, the heater usually needs to be operated twice a day, once in the morning and once in the evening. During the more moderate seasons, or in moderate climates, the heater may need to be operated only once, usually in the early evening, to supplement the heating requirements to maintain comfortable temperatures throughout the night. Other variations in operation, such as the number of loadings or the amount of wood used per loading during each firing, may also result in increased comfort. The operator should experiment with several variations of operation to determine the best performance for various seasons.
Properly operated, these brick masonry heaters are very effective in supplying radiant heat to the area of the building surrounding the heater. These heaters are not only good sources of heat, but have wood-burning efficiencies of 80 to 90 percent.
Building Code Requirements
There are no major model building code requirements which specifically address brick masonry heaters. For the most part, the building code requirements for fireplaces and chimneys are applicable to brick masonry heaters except for those requirements which address the dimensioning of the firebox and smoke chamber. All building code chimney requirements and clearances for combustibles are applicable.
There are, however, two concerns regarding safety which apply to the brick masonry heaters that are not presently listed in the major model building codes. The first concern is the integrity of the heater's enclosing walls. The walls forming the shell of the brick masonry heater should be at least two wythes of brick thick so that major cracks do not occur in the brick masonry heater. It is advisable to provide a nominal 1-in. (25 mm) air space between the two wythes. This will prevent cracks from penetrating through the interior to the exterior of the heater. Filling this 1-in. (25 mm) air space with compressible, non-combustible material, such as fiberglass insulation, will insure this separation. The two wythes should be tied together with corrosion-resistant metal ties. The insulation used to maintain a compressible space between the two wythes of brick should not affect the overall thermal performance of the brick masonry heater. To add to the integrity of the exterior wythe of the brick masonry heater, horizontal joint reinforcement should be placed in about every sixth course. Horizontal joint reinforcement should not be used on the interior wythe because the extreme differential thermal movements may deteriorate the mortar joints.
The second concern is the temperature of the exterior surfaces of the brick masonry heater walls. The highest