My mother didn’t raise no nincompoop, but she did raise one heck of a lazy man. So, when I got older and decided I was going to heat with wood instead of fossil fuels, I didn’t go the route of most homesteaders. Instead of a castiron woodstove that would need to be fed constantly, I installed an efficient, less labor-intensive masonry heater in my home.
Essentially, a masonry heater is an all-masonry fireplace designed to capture the heat produced by a single load of firewood that burns rapidly at high temperature. The heater then radiates the stored heat over a long period of time, often up to a full day. You may have heard of masonry heaters by different names, such as Russian fireplaces, German stoves, Finnish fireplaces, or maybe even kachelöfen. These names all refer to a version of a masonry heater.
Most of fall and spring, all I do to heat my 900-square-foot house is put a full load of wood — which for me is about 25 pounds — into the firebox of my masonry heater, get it burning with some newspaper and kindling, close the door, and then sit back and watch my mini-inferno. I don’t have to touch another stick of firewood for the rest of the day. In winter, I have to do this twice every day — one load of fuel before breakfast, and then one more in the evening before I go to bed. I can go to sleep knowing there’s no fire burning in the house, but the heat is still on — no getting out of a warm bed in the middle of the night to throw another log or two into the woodstove.
For those of you who work away from home all day, this probably sounds mighty appealing. You can heat your home with wood even if no one is around to fuel the stove, and then come home after a long day to find your home warm and comfortable.
How Does It Work?
We usually expect heat to be generated only when something is burning. So how the heck do you heat a living space for 12 hours or more without constantly stoking a fire with fuel? The short answer is “with a battery.”
We walk on a huge battery every day and call it “Earth.” The sun warms the Earth’s surface, which is where warm breezes come from. The heat storage capacity of the world is what makes living on it possible. That same capacity is built into a masonry heater. Most masonry heaters weigh between 1 and 5 tons. That’s 2,000 to 10,000 pounds of heat-storing masonry mass!
Masonry heaters channel hot exhaust from a fire through a winding path of flues built into the mass, warming every ounce of that massive structure. After they’re warm, they stay that way for a long time, like a concrete driveway in hot summer sun or that big rock next to your favorite swimming hole.
Masonry heaters come in countless different designs and dimensions, from squat and wide to tall and thin. Yet, they all share a common design element in that they rely on a long maze of flues. This is where the heat exchange takes place. The exhaust from the fire leaves the firebox and circulates many feet along a path that sometimes goes down, sometimes up, sometimes left, sometimes right, sometimes forward, sometimes backward, before it finally exits the heater and floats up the chimney (see illustration in the slideshow).
All the flues are made with refractory masonry materials that absorb the heat from the exhaust and charge the massive heat-storage battery. As a masonry heater designer, my goal is to incorporate the right amount of surface area for heat exchange. I want the maximum amount of heat extracted before the exhaust reaches the chimney. If done correctly, just enough heat will be left for the exhaust to rise up the chimney and out of the house.
The result is high-efficiency heating. Heating efficiency is a measure of how much of the heat generated by burning fuel actually stays in your house, contributing to your comfort. When I design for maximum heat exchange in the heater, I’m maximizing heating efficiency too.
After the fire is out and no more heat absorption is happening, the heat stored in the mass starts migrating to the exterior of the masonry heater. As the exterior of the heater gets warmer and warmer, it emits more and more radiant heat into the living space. It also directly heats air that passes by the surface of the heater. When properly designed, it will continue to radiate and transfer heat from its exterior surfaces for many hours after the fire dies. The design of a masonry heater determines the length of a heating period, typically at least 12 hours. Thus, two firing sessions per day are sufficient to heat a living space for a full day, even on the coldest days of winter.
One of the best things about a masonry heater is that it mostly produces radiant heat. If you’re unsure what that means, go outside on a calm, sunny day, close your eyes, and turn your face to the sun. The warmth you feel is the radiant heat of the sun that traveled millions of miles to brush your rosy cheeks. The radiant heat from a masonry heater has exactly the same feeling. It’s not a heat that drives you out of the room, like that from a metal woodstove when it’s glowing cherry-red. Masonry heaters produce a calm, persistent, and gentle warmth that invites you in like Grandma offering fresh-baked cookies.
The human body responds very positively to radiant heat. Your skin relaxes when it comes into contact with gentle radiant heat. Even the blood vessels in your skin respond positively, opening and promoting good circulation and warmth.
Most homes these days aren’t really heated at all. Forced-air furnaces — and woodstoves too — mainly heat air. Warm air from a furnace serves as a blanket that reduces heat loss from the people inside the heated space. If you heat with a forced-air furnace, the air temperature in your house is probably around 70 degrees Fahrenheit. But your core body temperature is around 99 degrees, and your body surface temperature is around 80 degrees. You can’t heat an 80- to 100-degree body using 70-degree air. It would be like trying to reheat leftover chili using an ice cube!
Which brings me back to the masonry heater: A functioning masonry heater will usually have a surface temperature between 120 and 200 degrees — warmer than your body.
One of the benefits of the moderate surface temperature of the masonry heater has to do with safety. You can briefly touch a 200-degree masonry surface and not get burned. That’s a lot different than the blistering capability of a hot metal woodstove. In this way, a masonry heater is safer for children to be around.
Praise for Masonry
Mark Twain traveled to Europe in the 1800s and experienced masonry heaters for the first time where they originated, in the cold regions of the Old World. He praised them up and down in Europe and Elsewhere, writing:
“All day long and until past midnight, all parts of the room will be delightfully warm and comfortable, and there will be no headaches and no sense of closeness or oppression. In an American room, whether heated by steam, hot water, or open fires, the neighborhood of the register or the fireplace is warmest — the heat is not equally diffused throughout the room; but in a German room, one is as comfortable in one part of it as in another. Nothing is gained or lost by being near the stove. Its surface is not hot; you can put your hand on it anywhere and not get burnt. Consider these things. One firing is enough for the day; the cost is next to nothing; the heat produced is the same all day, instead of too hot and too cold by turns; one may absorb himself in his business in peace; he does not need to feel any anxieties of solicitudes about the fire; his whole day is a realized dream of bodily comfort.”
Besides the benefits in comfort Twain mentions, masonry heaters also burn cleanly: Dry wood with the right amount of oxygen will burn completely and with virtually no smoke. A well-designed masonry heater achieves about 95 percent combustion of the fuel at temperatures exceeding 1,100 degrees. The predominant exhaust is carbon dioxide and water.
The effect of such clean burning, combined with a masonry heater’s designed ability to store the heat of combustion, provides an additional benefit in that it uses less firewood than you might imagine. When living in my previous home of 2,000 square feet, I compared notes with a friend who lived in a home with the same square footage (though his was actually better insulated). He was using 8 to 10 cords of wood to heat his house each year with a cast-iron woodstove, while I was using 4 to 5 cords in my masonry heater. Not an empirical study, by any means, but it sure was an eye-opener for him. Poor guy splits enough wood in one year to heat my house for two years!
Some masonry heaters incorporate cooktops or ovens (or both), expanding the heater’s versatility. In a cookstove, flue gases usually come in contact with a cast-iron cooking surface before moving through the masonry mass, which then captures the residual heat. The bake-oven option is a way of using the same fuel that heats your living space to cook food. The low-ceilinged oven is unique in the baking world: It cooks food with convection, conduction, and radiant heat, all at the same time.
One of the great advantages of using a masonry heater is that it is just as effective and efficient regardless of the wood species used for fuel. Contrary to popular belief, softwoods aren’t necessarily a poorer choice than hardwoods for heating. In truth, all wood species have roughly the same heating capacity per pound of dried wood fuel. Softwoods are a real problem for those with typical metal stoves because the fuel burns so fast. If you damper the fire from a high-sap softwood, you generate lots of creosote and smoke. This is not an issue with a masonry heater, in which all fuel is burned quickly and at high temperatures with the right amount of oxygen for clean combustion.
Weighing the Options
Less work. Less wood. Gentle, persistent heat. No constant stoking. Less likely to burn your kid’s fingertips. And did I mention how beautiful they can be? My, who wouldn’t want a masonry heater? (Well, besides you folks who like working harder than you have to.) But before you place your order, there are some things to consider.
First, masonry heaters are doggone heavy. They need a firm foundation. The most typical way this is done is by building a footer and concrete block foundation up to the main level from the basement or crawl-space floor. On that structure, a slab is then poured on which a masonry heater can be built.
Also, a masonry heater is usually designed to radiate heat from all surfaces — front, back, sides, top, and sometimes even the bottom. So, the best location for one is in the center of a living space rather than against an outside wall. A lot of people make a masonry heater a room divider, placing it between a dining room and living room, or between a family room and kitchen. Open floorplans, without a lot of walls, ensure that radiant heat travels unimpeded through the house. None of these are strict requirements, just best-case scenarios.
The central location is also functional from the venting standpoint. An effective, efficient, and trouble-free masonry heater requires a chimney with good, reliable draft. The ideal way to make that happen is to have the chimney inside the heated space of the house as much as possible. This happens naturally from a central location so that the chimney eventually exits the home close to the ridge of the roof — the tallest part of the house. This also minimizes the possibility of roof leaks. A chimney that exits lower on the roof is downstream from precipitation and is thus more likely to catch dirt and debris that may degrade the watertightness of protective flashing over time.
And, finally, you won’t get all the benefits, beauty, and functionality at a low cost. Masonry heaters are the Cadillacs of the wood-heating world, and they have the price tag to prove it. If you hire a masonry heater professional to build one for you, plan to pay about what you would for a new car, from about 10,000 to 30,000 dollars — or more for something extra-large, truly custom, and one-of-a-kind.
This may sound like a lot of money. But this is an all-masonry, lifetime, heirloom appliance. You’ll enjoy it, and it will still be performing at peak efficiency when the next generation takes over. For decades after installation, the heater will keep on giving lots of radiant comfort with little effort on your part. I like to remind people that they do, indeed, spend the same kind of money for their cars and trucks, and then buy yet another vehicle a few years later. Your masonry heater won’t lose all its value after you drive it off the lot. It’s a rock-solid investment — pun intended.
Ken Matesz attributes his long career of building masonry heaters to a desire to avoid cutting firewood. Find him online at Masonry Heaters by Ken Matesz and Masonry Heater Store, LLC. Both websites offer his book Masonry Heaters.