Keep Your Home Warm With a Masonry Heater

Enlarge Image Image Gallery The custom installation process for masonry heaters is an opportunity for creative design. Photo by Stuart Davies

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You don’t have to wait for technological advances to create an energy-efficient, nonpolluting, convenient, and comfortable method of heating your home. The technology is already here—and has been used to heat the famous Roman baths and warm beds and floors in China and Korea for centuries. Europeans perfected masonry heating stoves 400 years ago, during what we might call the first energy crisis, when it became clear that conservation measures were needed as citizens in growing villages demanded more and more wood for heating and cooking.

In the late 1700s, King Gustav III of Sweden charged two men, F. Wrede and C. J. Cronstedt, with the job of designing an efficient masonry heater. The product of their efforts was an efficient fireplace that is very similar to heaters being built today, says Ken Matesz, a certified heater mason who operates Fountainhead Natural Homes in Swanton, Ohio.

Unlike fireplaces and wood stoves, masonry heaters don’t guzzle wood or suck warm air out of your home and up the chimney, resulting in a net loss of heat. They don’t produce and deposit creosote on the inside of your chimney, creating a fire hazard, nor do they pollute the environment. When used properly, a masonry heater contributes no more pollution than what occurs from wood naturally rotting on the forest floor, Matesz contends.

What is a masonry heater?

A masonry heater is a wood-burning appliance made of solid masonry that acts as thermal mass, which absorbs heat from a relatively short, hot fire, then releases it as slow, gentle radiant heat that lasts twelve to twenty-four hours after the fire goes out. In the United States, masonry heaters usually fall into one of four categories. “Since the concept of masonry heating is of European origin, we tend to group them by characteristics they had in their country of origin,” explains Matesz. “So, we have a Finnish contraflow, a Swedish, a Russian, and the Grundofen. All types have the same general characteristics of high-mass masonry construction, heat exchange channels that make at least one 180-degree turn after leaving the firebox, and stored heat that lasts many hours after the fire is out.” (See “A World of Choices,” page 81.)

Masonry heaters don’t operate like conventional wood burners. First, the firebox—designed to facilitate quick heat—is loaded with fuel (wood), and a fire is started. The fire is burned with plenty of air but with doors closed. A narrow throat above the firebox contributes to fast burning and turbulence. Another chamber, above the throat, swirls and mixes turbulent gases at high temperature, until they are thoroughly consumed. From here, the exhaust circulates through a lengthy heat exchange channel (a sort of prechimney with twists and turns) that draws heat from the exhaust into the masonry mass. Finally, the significantly cooled exhaust exits the system through a relatively ordinary chimney.

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