Masonry heaters good, but demand skill

by Steven Maxwell

Steven Maxwell is technical editor of Canadian Home Workshop magazine. He can be reached at smaxwell@onlink.net. This article first appeared in the Toronto Star on November 28, 1998. It is reprinted here by permission of the author.

One of the favourite indulgences of us 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. Sure, we've got some very efficient fireplace inserts, pellet-burning furnaces and woodburning stoves, but if you look at the facts, you¹ll see that clean, efficient woodburning has been done before, and done very well in much simpler ways.

Ancient European cultures, whose survival depended on making wise use of dwindling wood supplies, developed a simple woodburning technology that rivals the efficiency of anything that¹s come off the drawing board lately. The item that delivers this performance is now generically called a 'masonry heater' on this side of the Atlantic. And according to extensive in-home tests audited by the Environmental Protection Agency (EPA) in the US, they regularly achieve some of the cleanest combustion results ever recorded for woodburning appliances. Masonry heaters continue to be popular in Europe, too. Over 90% of new homes in Finland include one.

I've heated my home with a masonry heater for the past eight 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. The masonry heater option is a very good one, but beware.

How masonry heaters work

A masonry heater is a large, 500kg to 1000 kg woodburning appliance that¹s made of high-temperature refractory materials, and stone or brick. Although masonry heaters look something like a fireplace, they¹re quite different. The firebox is designed to burn a fast, hot, clean fire that consumes 10kg to 20 kg of wood in about an hour and a half. Searing combustion temperatures of 800C to 900C are common. During operation, this intense heat is absorbed into the surrounding masonry, then released slowly into 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 many other wood-burning systems.

More than meets the eye

The Austrians build some of the finest masonry heaters in the world today, and it¹s no accident that the trade is highly regulate there. 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 of the trade, and assures homeowners of the highest quality workmanship and performance.

What¹s 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, the virtue of high temperature combustion that gives masonry heaters their superior performance, 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 Canadian-made system, it has deteriorated badly due to the high operating temperature that's normal for masonry heaters. 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 use. There have also been problems with the glass doors the system originally came with. After numerous sets of replacement panes that have all cracked due to the heat (at $60 a pop), I now have reliable, solid-steel doors I built myself. Dozens of appeals to the manufacturer yielded no help from them in the matter.

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 with my ready-made unit. 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

Temperature-related problems originate from two sources -- material deterioration from the high combustion heat, and mechanical degradation due to the large degree of expansion and contraction that occurs with the wide temperature swings between burning and non-burning modes. This is especially true where metal and masonry meet.

Building a long-lasting masonry heater demands all the durability of the best refractory products, and a keen knowledge of how to put them together. 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 don¹t just talk to the recreational wood burners, either. You want input from people who actually heat their homes with masonry heaters burning at the high temperatures that are necessary for proper performance. Also, be sure to contact The Masonry Heater Association of North America (802-728-5896 or on the Web http://mha-net.org/ ), an independent trade group that promotes sound construction and design.

A sustainable option

I originally opted for a masonry heater because I was convinced it was a sustainable, environmentally-sound way to heat my home. I still feel that way. Low emissions contribute minimally to air pollution, and the fact that wood is the fuel means that new carbon isn¹t added to the atmosphere. Just be sure you're investing in the kind of good design and workmanship needed to make your masonry heater sustainable too.

Steven Maxwell
455 Bailey Line Road
Evansville, Ontario P0P 1E0
smaxwell@onlink.net