Make Cozy Happen with Masonry Heaters

Reader Contribution by Eric Schroeder
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So much of any new learning is learning new language. Technical definitions exist that define a masonry heater in terms of physical characteristics, but I want to come at this from a different angle. I want to start with the problem. Finding fuel has always been a challenge for humans. Fuel becoming harder to find is a reality of our times, but that alone is not the real problem.

The real problem is that it gets cold, and I’m too stubborn to move to Florida in the winter. Winter is beautiful in New England. I love when the snow piles on, and I get to walk in the woods in the stillness of a winter day but I have to admit, it hurts if I stay out too long. There are lots of ways you can make a house warm, but a masonry heater solves the problem of cold in a way that also creates what the Danes call hygge, that wonderful coziness that makes us feel warm, safe, secure and, somehow, loved.

A masonry heater burns a charge of wood (though some use coal or even straw) quickly and cleanly and then stores the heat in a thermal mass, typically brick, stone, or tile. You’ll burn for an hour or two but warm the space for much longer.

As we consider what a masonry heater is, I want to focus on attributes that all heaters share, so that we encompass all of many worldwide styles with our explanation. And we don’t want leave anyone out simply because their heater doesn’t look like ours. The principles are simple and elegant. A masonry heater takes advantage of the natural forces at work and the whole is greater than the sum of its parts.

A good masonry heater does three things:

1. Burns (typically) a day’s worth of wood with excellent combustion efficiency
2. Absorbs the heat thus produced into its structure
3. Radiates that heat into the cozified space

Burning wood completely. Wood burns very well at a high temperature and with plenty of oxygen. Well designed masonry heaters burn without producing visible smoke at all. That’s due to a number of things that will be discussed later. For now, it suffices to say that a well designed firebox supports combustion at over 1,500 to 2,000 degrees Fahrenheit (although we have seen 2,000-degree probes burn up in our fireboxes). A well designed masonry heater burns the wood and the smoke, so creosote is not a concern. The elements that condense to form dangerous creosote are completely burned and therefore are not present in the exhaust.

Absorbing and storing heat. A masonry heater absorbs heat as the exhaust moves through channels and/or chambers made of firebrick. The hot exhaust warms the inside of the channel walls, and that heat moves through the material, warming the outer surface of the stove.

Making cozy happen. The third part, transferring the warmth to the home is where the cozy happens. Have you ever been near a stone that had been in the direct sun all day on a cool day? By day’s end, that stone is warm, and it feels fantastic to touch it. A large enough stone will radiate heat all night, just like our stoves. There are different ways to build masonry heater walls, but because they are masonry, they all serve the purposes both of storing and releasing the energy into the home. The warmth is released primarily as radiant energy, which has many documented health benefits and feels wonderful to be around.

Masonry heaters developed at different places around the world and at different times, and the different peoples dealt with the design challenges provided by high temperatures and heating cycles in different ways. I’ll discuss those factors and how they are dealt with in future posts.

Eric Schroederis a masonry heat expert who has been designing heaters since 2006, innovating around stove shape, size, firebox design, and heat exchange layouts. Connect with Eric at Eric Schroeder Stoves and onTwitter, and read all of his MOTHER EARTH NEWS postshere.

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