Masonry Heater - Characteristics

Characteristics

As the name says, it is made of masonry - namely brick (firebrick), tile, stone, stucco, or a combination of these materials - rather than steel or cast iron. It is freestanding, and usually requires special support to bear its weight. It consists of a firebox and heat-exchange channels or partitions that provide additional surface area. These absorb heat from the hot exhaust gases before the gases exit into the chimney. The fire in a masonry heater burns much hotter than in a metal stove. Very hot fires reduce emissions significantly. When not being fired, the connection from the masonry heater to the chimney sometimes has a damper to prevent heat from escaping up the chimney; the heat is then radiated from the masonry.

Masonry takes longer to heat than metal; but once warm, the heater will radiate this heat over a much longer period of time and at a much lower temperature than a metal stove would use (the metal is hot only when there is a fire burning inside the stove and for a short time thereafter). A masonry heater is warmed by fires that burn for a short time; it is mostly the heat stored by the heater's mass that heats the living space. Both in Europe and in America seating and even beds are occasionally built adjoining the masonry stove; this is possible because the heater's exterior surfaces are cool enough to touch safely.

Heat stress is a major concern during the construction of masonry heaters. Differences in temperature inside the masonry core of the heater can result in differential expansion. A skilled heater mason knows how to provide for this stress when designing and constructing the heater, thereby preventing uneven expansion from causing cracking in the exterior.

Masonry heaters take a long time (from 5 hours up to two days) to get up to the right temperature and so are not always practical for taking the chill off a single cool evening or morning, but they are well-suited for long periods of cold weather because they store heat so well and provide dependable, even heat all day and night. Because the radiant heat is given off at a low level a masonry heater is not likely to overheat a home the way a metal stove might in warmer parts of the year like fall or spring.