"Masonry heaters are clean and reliable, but heed these warnings" by Steve Maxwell
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Saturday, November 27, 1999
One of the favourite indulgences of modern people is the belief that we’re the first in history to invent great ways of doing things. This is especially true in the field of wood heating. Ancient European cultures, whose survival depended on making wise use of dwindling wood supplies, developed a simple wood-burning technology that rivals the efficiency of anything that’s come off the drawing board lately. The device is called a masonry heater on this side of the Atlantic, and according to tests audited by the Environmental Protection Agency (EPA) in the U.S., they regularly achieve some of the cleanest combustion results ever recorded for wood-burning appliances.
I’ve heated my home with a masonry heater for the past nine seasons, and so have two of my friends. Although we’ve all enjoyed clean combustion and surprisingly even heat output over the course of the day, there are some things I’d like to warn you about.
How masonry heaters work
Masonry heaters are 500 kg to 1000 kg woodburning appliances made of high-temperature refractory materials and stone or brick. Although masonry heaters look like a fireplace, they’re different. The firebox is designed to burn a fast, hot, clean fire that consumes 10 kg to 20 kg of wood in about an hour and a half. Searing combustion temperatures of 800°C to 900°C are common. During operation, this intense heat is absorbed by the surrounding masonry, then released slowly to the room over the course of 12 to 24 hours.
The big advantage of the masonry heater is that it provides hot, clean combustion, plus a slow release of heat into the room – a combination not offered by most other wood-burning systems. The Austrians build some of the finest masonry heaters in the world, and it’s no accident that their trade practices are highly regulated. Construction of masonry heaters is the sole province of members of the Stovemason’s Guild – a centuries-old alliance that preserves and accumulates critical knowledge, assuring homeowners the highest quality workmanship and performance.
What’s all the fuss about, you say? How much do you really need to know to build a big, brick box with a chimney? Lots. As I’ve discovered through personal experience, the virtue of high-temperature combustion can also cause problems that are difficult to anticipate, and even harder to remedy after the fact.
Even though my masonry heater is a pre-fabricated system, it has deteriorated badly due to the high operating temperature. If it weren’t for my own work retrofitting the inside of the firebox with high-temperature brick and plaster, my heater would have failed after just three years. A friend of mine had his masonry heater built from scratch by a fireplace mason according to a plan, and is experiencing the same temperature-related problems I did. Another friend, with a unit built on-site by a masonry heater specialist, has had no trouble. Perhaps the Stovemasons know something after all.
Understanding the challenge
Before selecting a prefab unit or contractor for your job, ask for references from homeowners who have used the products for at least three years. And don’t just talk to recreational wood burners, either. You want input from people who actually heat their homes with masonry heaters. Also, be sure to contact The Masonry Heater Association of North America (802-728-5896 or http://mha-net.org/), an independent trade group that promotes sound construction and design.
Steve Maxwell is technical editor of Canadian Home Workshop Magazine. Write Steve Maxwell, c/o The Ottawa Citizen, 1101 Baxter Road, Box 5020, Ottawa, K2C 3P8. Please include a stamped, self-addressed envelope. E-mail: smaxwell@onlink.net
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