masonry stove or heater
Granite and marble masonry heater by William Davenport. www.turtlerockheat.com.
A masonry stove or heater, also known as a Russian, Siberian, or Finnish fireplace, is a type of heating appliance similar to a conventional fireplace, but much more efficient and clean burning. As their name suggests, these stoves are made of masonry and have long channels through which combustion gases give up their heat to the heavy mass of the stove, which releases the heat slowly into a room. Masonry stoves produce more heat and less pollution than any other wood- or pellet-burning appliance (see wood stove and pellet stove).
Masonry heaters include a firebox, a large masonry mass (such as bricks), and long twisting smoke channels that run through the masonry mass. Their fireboxes are lined with firebrick, refractory concrete, or similar materials that can handle temperatures of over 2,000°F (1,093°C).
A small hot fire built once or twice a day releases heated gases into the long masonry heat tunnels. The masonry absorbs the heat and then slowly releases it into the house over a period of 12–20 hours. Masonry heaters commonly reach a combustion efficiency of 90%.
Most are intended for burning wood, but they were historically designed to burn almost any type of solid fuel. The relatively small, but intense fire also results in very little air pollution and very little creosote buildup in the chimney. Because most of the heat from the fuel is transferred to the masonry and slowly released into the room over the day, this type of heater does not need to be loaded with fuel as often as other types of wood heating appliances. In addition, if the masonry heater is built where sunlight can directly shine on it in the winter, the heater will absorb the sun's heat and release it slowly into the room.
A wide variety of masonry heater designs and styles are available. Larger models resemble conventional fireplaces and may cover an entire wall. Smaller models take up about as much space as a wood or pellet stove. They can be custom-built or purchased as prefabricated units. Some large designs may cost $5,000 or more. Plans and kits are available, but they are not easy do-it-yourself projects and require experience in working with masonry.
In addition to their expense, masonry heaters have one significant disadvantage when compared to conventional wood stoves and fireplaces: They cannot provide heat quickly from a cold start.
See also masonry oven.
Masonry heater definition
A formal definition of what counts as a masonry heater was adopted by the Masonry Heater Association of North America in 1998. It runs as follows:
A masonry heater is a site-built or site-assembled, solid-fueled heating device constructed mainly of masonry materials in which the heat from intermittent fires burned rapidly in its firebox is stored in its massive structure for slow release to the building. It has an interior construction consisting of a firebox and heat exchange channels built from refractory components.
Specifically, a masonry heater has the following characteristics:
a mass of at least 800 kg (1760 lb.) tight fitting doors that are closed during the burn cycle an overall average wall thickness not exceeding 250 mm (10 in.) under normal operating conditions, the external surface of the masonry heater, except immediately surrounding the fuel loading door(s), does not exceed 110°C (230°F) the gas path through the internal heat exchange channels downstream of the firebox includes at least one 180-degree change in flow direction, usually downward, before entering the chimney the length of the shortest single path from the firebox exit to the chimney entrance is at least twice the largest firebox dimension