As today’s home construction and renovation projects tend more and more to high thermal performance, and with members of the public more and more interested in renewable technologies, Masonry Heaters occupy a critical place in the Architect's tool bag. Simply knowing about masonry heaters will differentiate you from your competition, but an understanding of what's possible aesthetically will add an exciting element of artistry to your projects.
Never in the history of the fireplace has there been a technology that allows for such a varied expression of aesthetic.
Masonry Heaters give you one more way to individualize your homes to your clients needs, and adding a tremendous value to your services as their design professional.
Masonry Heaters have existed in Europe, Scandanavia, and Russia for 700 - 1000 years. Long traditions of building heating stoves, cooking stoves, and baking ovens stretch back further even than that.
In order to get all the heat energy out of wood, it must be burned at a high temperature. Masonry heaters to this first, and secondly they harvest that heat through a thermal mass which moderates it to provide 12 hours or more of gentle, even radiant heat from an hour to an hour and a half of wide open, full throttle, combustion.
- Thermal Mass
A thermal mass is any object which absorbs heat. It is akin to a heavy object: It takes a large push of energy to get it rolling, but will tend to remain rolling once it's started. The thermal mass in a masonry heating system takes a large amount of heat in a short period and keeps rolling a long while.
- Design Theories
Masonry heaters operate on chimney draft. Draft pulls the combustion products through the system, and provides fresh air for the combustion reaction. Balancing the draft produced by the chimney with the resistance to flow of the heat exchange system is the science of masonry heater design. Making all that look as good as it feels is the art of masonry heater design.
Different regions have come up with different traditions regarding design, construction, and use of masonry heaters.
The most common tradition shown here in the USA is the Finnish Contraflow heater. A brick box measuring about 3 feet deep and 4 feet wide, the contraflow stove is fairly easy to build and can be a very efficient device. It is so named because the two heat exchange channels that move down either side of the firebox conduct the gas inside the stove from it's top to it's bottom, where it exits the stove. Room air flows contrary to this, as it is heated it moves up the outside wall of the stove.
A Swedish design using both a set of down flowing channels and a set of up flowing channels, kakelugn tend to be smaller than contraflow stove, lighter, and a great many have been made that are round.
Too many types of stoves have been built in Russia to call any one design "Russian." Typically constructed of brick, and commonly including cookers and bake ovens, Russian stoves tend to be heavier and contain more thermal mass than their European counterparts; perhaps this is a testimony to the roughness of the Russian winter.
Kachelofen / Grundofen
In Germany, Austria, Switzerland, Northern Italy, and Eastern Europe one finds a stove building tradition based on structural tiles called: "Kachels." Stoves designed according to this tradition are lighter and more flexible in shape than most other stoves. Sized according to heating need, with an almost infinite array of shape possibilities.
Masonry Heater output is based on three factors:
1) Surface area - square footage of exposed heater face.
2) Temperature - temperature of the stove relative to ambient temperature
3) Emissivity - quality of a material describing how much energy it will output for a given surface area and a given temperature.
No matter how efficiently you get the surface warm, once you have a given surface area at a given temperature it will put out a given amount of energy. A smaller stove with a higher emissivity or a higher temperature will have a higher output. A bigger stove with a lower emissivity and a lower temperature will put out less energy.
Because radiant heat travels like light, and we are all familliar with light bulbs, the following is the simplest way to consider the initial impact of a Masonry Heater in a given space:
Think of a floor lamp without a shade in the place you are considering placing the stove. All the places that are lit by the light will be impacted by the radiant heat waves from the stove. The more consistently the stove is kept warm, the further the heat will spread from there.
There is, of course, a limit to how far the heat will go, and how many obstacles (in the form of walls, hallways, and doorways) the heat will negotiate.
Masonry Heaters fit right in to today's open concept architecture, and can be blended seamlessly into any decor.
As mentioned above, the stove will be as large as the heat output required. Shape will depend largely upon the skill and cunning of the heater builder.
- Thermal Mass