How do you size a masonry heater?

The figure must be multiplied by the overall thermal efficiency of the stove, heater or chimney. The difference can be enormous and can range from -10% to 90%, depending on the unit used.

How do you size a masonry heater?

The figure must be multiplied by the overall thermal efficiency of the stove, heater or chimney. The difference can be enormous and can range from -10% to 90%, depending on the unit used. American Masonry Heater and Oven produces affordable, efficient and easy to use heating cores and wood ovens for the builder, all in kit form. Whether you do it yourself or use a bricklayer, assemble any of our standard basic kits in two days.

The result is a functional, efficient, durable and beautiful wood heater or oven. All basic kits are 100% made in the United States. Tests help establish the performance of a masonry heater with respect to particulate emissions, combustion efficiency and overall efficiency. In terms of masonry heaters, combustion efficiency describes the intensity with which the heater burns the cordwood fuel load.

Overall efficiency describes how well the stove transfers the energy released by the burning of the wood fuel source to the usable thermal energy radiated by the heater. A soapstone stove with a smaller mass retains less heat and cools faster than a large one. A larger masonry heater stores more energy, which is released slowly into the room and keeps it warm for a long time. However, a Tulikivi soapstone heater always far outperforms a wood stove, for example, which only emits heat for a relatively short period of time.

One of the great designers and researchers of masonry heaters in the mid-20th century was a Finnish researcher named Asp. When I (Albie) began my trips to Finland in the late seventies, my friend from Helsinki, Finland, Heikki Hyytiainen, mentioned Asp's work and we were able to find one of his books in Finnish, which I now have. Among other things, Asp worked hard to introduce what designers of masonry stoves and stoves usually call secondary air, that is, air that does not pass through the grill, but is introduced into the fire through the walls or through the throat of the combustion chamber above the fire. When Albie organized the first practical Finnish chimney construction workshop in North America in the late 1970s, Heikki traveled to Lincolnville, Maine, to run the workshop.

As I recall, about sixteen interested masons and others from the United States. The US and Canada went to the heater workshop, many of them on motorcycles. On site, we discussed the topic of secondary air and introduced in that first heater a very simple system of air over fire with a couple of small tubes that carried air above the fire, but we didn't have a clear or scientific knowledge of what we were doing. It has a fairly normal size when it comes to masonry heaters; it has a basic size close to 24 x 36, the same as the one you are researching.

However, look in the Austrian phone book for a stove installer, as they are called there, and you'll find 20 to 40 in a medium-sized city.

Carolyn Signor
Carolyn Signor

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