Masonry heater

Masonry heater

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A masonry heater is a device for warming a home (or any interior space) that captures the heat from periodic burning of fuels (primarily wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

), and then radiates that heat over a long period at a fairly constant temperature. The technology exists in many forms from the Roman hypocaust
A hypocaust was an ancient Roman system of underfloor heating, used to heat houses with hot air. The word derives from the Ancient Greek hypo meaning "under" and caust-, meaning "burnt"...

to the Austrian/German kachelofen. The hypocaust is a system for heating the floors and walls of buildings (especially bath
Bathing is the washing or cleansing of the body in a fluid, usually water or an aqueous solution. It may be practised for personal hygiene, religious ritual or therapeutic purposes or as a recreational activity....

s) using the smoke
Smoke is a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires , but may also be used for pest...

 and exhaust of a single fire. In Eastern and Northern Europe and North Asia, these kachelofens (or steinofens) evolved in many different forms and names, such as a Russian Stove/Fireplace
Russian oven
.A Russian oven or Russian stove is a unique type of oven/furnace that first appeared in the 15th century. It is used both for cooking and domestic heating. The Russian oven burns firewood or wood manufacturing waste....

 , a Finnish Stove (in Finnish: pystyuuni or kaakeliuuni, "tile oven") and the Swedish Stove (in Swedish: kakelugn, "tile stove" or "contra-flow stove") associated with Carl Johan Cronstedt
Carl Johan Cronstedt
Carl Johan Cronstedt was a Swedish architect, inventor, Earl, noble, civil servant, scientist and bibliophile.-Biography:Cronstedt was the son of Jakob Cronstedt and Margareta Beata Grundel born in 1709 in Stockholm, Sweden. He married Countess Eva Margareta Lagerberg in 1744.Cronstedt became a...

. The Chinese developed the same principle into their Kang bed-stove
Kang bed-stove
The Kang is a traditional long sleeping platform made of bricks or other forms of fired clay and more recently of concrete in some locations. Its interior cavity, leading to a flue, channels the exhaust from a wood or coal stove...

. The masonry heater has gained new popularity in recent times through its modern design applications and foremost its distinct heating efficiency.


As the name suggests, it is made of masonry, rather than steel. It is free-standing and requires a significant support structure to bear its large weight. It consists of a firebox and heat exchange channels or partitions that provide additional surface area to absorb heat from the hot exhaust gases before they exit into the chimney
A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the...

. Since the firebox is masonry, rather than metal, fires can and do burn much hotter than in a metal stove. These hot fires substantially reduce emissions. When not being fired, the connection from the masonry heater to the chimney is sometimes damped to help prevent heat from escaping up the chimney. The heater then radiates heat from the masonry exterior, which may be brick, tile, stone, stucco, or a combination of these materials.

Masonry takes longer to heat than metal; but once warm, the heater will also radiate this heat over a longer period of time, and at a much lower temperature than a metal stove (which is hot only when there is a fire burning inside the stove and for a short time thereafter). A masonry heater is warmed by infrequent fires that burn a short time; it is the stored heat from the fire that heats the living space. In Europe and in America, builders sometimes incorporate seats and even beds into the masonry stove because the external surfaces of a properly used heater never get hot enough to burn skin, so are very safe to touch.
Heat stress is one major concern in the construction of masonry heaters. The differences in temperatures inside the masonry core of the heater can result in differential expansion. A skilled heater mason knows how to properly account for this stress when designing and constructing the heater, thereby preventing uneven expansion and cracks in the exterior structure.

Masonry heaters take a long time (from 5 hours up to two days) to get up to temperature, and so are not always practical for "taking the chill off" a single cool evening or morning. Rather, when put into operation, they provide dependable, even heat all day and night. They are well-suited for long periods of cold weather because they store heat so well. Because the radiant heat is at 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.

Fuel sources

These heaters are primarily fired by wood, and those fires are meant to burn hot and quick (never damped down, as is often the case with standard wood stoves). They are not burned continuously. This method of heating may have been a reaction to the dwindling resource of wood before the advent of coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

 and other mineral energy sources. Open hearth fireplaces were an important source of light, as well as heat, and with an "unlimited" supply of wood to fire them, there is no incentive to increase the efficiency of their heat output, which is rather poor. However, once firewood became a scarce resource, fireplace builders began to enclose the firebox to capture as much heat as possible.

Since masonry heaters burn hot and fast, they can accept any dry, split (usually three to five inches in diameter) wood. In some areas of Central and Eastern Europe, these heaters are sometimes effectively fired using grass
Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...

, straw
Straw is an agricultural by-product, the dry stalks of cereal plants, after the grain and chaff have been removed. Straw makes up about half of the yield of cereal crops such as barley, oats, rice, rye and wheat. It has many uses, including fuel, livestock bedding and fodder, thatching and...

, and hay
Hay is grass, legumes or other herbaceous plants that have been cut, dried, and stored for use as animal fodder, particularly for grazing livestock such as cattle, horses, goats, and sheep. Hay is also fed to pets such as rabbits and guinea pigs...

. It is also common in Eastern Europe to modify these efficient heaters so that they are connected to the gas network and are fueled with gas. Some modern models incorporate electric heating elements connected to timers. These are used only as a backup heat source during periods when the structure will be left unattended for long duration in winter (and therefore with no one to build a new fire in the heater each day or as needed) to prevent the structure from freezing.

Modern development

In recent years masonry heaters have changed their look considerably while maintaining the main function of providing radiant heat. Many modern masonry heaters do not incorporate ceramic tiles on the outer surface anymore. The refractory bricks are covered by a heat resistant plaster providing a more contemporary look. Another feature is the use of a glass door to cover up the combustion chamber. This not only provides the visuals of a burning fire, but also ensures immediate heat provision into the room. This is ideal in modern lifestyles when it cannot be ensured that the masonry heater is kept at temperature all day round. Once the firewood has burned down the heated up structure will take over the heating through radiation.
Modern masonry heaters are exactly calculated and computer simulated as to their internal flue passages, their efficiency and output and the corresponding amount of wood required. Through this it can be ensured that the heater exactly matches the requirements of the living spaces.

Further reading

  • Masonry Heaters: Designing, Building, and Living with a Piece of the Sun by Ken Matesz (Chelsea Green Publishing Co., 2010)
  • The Book of Masonry Stoves: Rediscovering an Old Way of Warming by David Lyle (Chelsea Green Publishing Co., 1984)

See also

  • Russian oven
    Russian oven
    .A Russian oven or Russian stove is a unique type of oven/furnace that first appeared in the 15th century. It is used both for cooking and domestic heating. The Russian oven burns firewood or wood manufacturing waste....

  • Rocket mass heater

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