The Incredible Masonry Heater

A lot of people who have discovered masonry heaters first discovered them as a box, like the heater at left. What I mean is that, chances are, they read about them somewhere (other than my book) and the accompanying photo or drawing was of a big, rectangular box. I call it the refrigerator. I find it disappointing that most people's first exposure to these amazing appliances leads them to believe that, if they want a masonry heater, they need to find somewhere in their home to fit in a big, clunky box.

Now, don't misunderstand.  I built that box that you see here.  And it works just great thank you very much.  And for all of you who love red brick and rectilinear shapes, I'm sure you find this very attractive.  But I still think that this rectangular red brick box should not be the way people are introduced to masonry heaters.

The picture below proves that it is not the case at all that you have to have a box to have a masonry heater.  This wonderful sample (and you can find even more such samples at http://www.kachelofen-stoisser.at/kacheloefen.php where this photo was pulled) of how masonry heaters become artwork, fun, and a centerpiece while also being the true heart of the home. Here, free-formed plaster tree branches meld with the heater in every direction and colorful, handmade tiles create visual interest without destroying the soft lines of the rounded surfaces of the masonry heater. Most of us, when we think of tiles, think of square, uniform, flat surfaces. A handcrafted masonry heater like this proves that everything is not always what we expect.

Masonry heaters do not need to be big boxes. They don't need to be intrusive behemoths in the living space. Quite the contrary, they should be a magnet for people. Think about your own human body. Can you point to any distinct, sharply defined rectangles or squares on the surface of your body? Obviously not. The whole human form is a continuum of rounded soft forms. But more importantly, in addition to its soft roundness, the living human form is warm. Most people eventually find a mate who is attractive to them. What is attractive about one's mate is both their form (physical) and their warmth (physical, emotional, and intellectual). Masonry heaters, too, can (and should) hold that attraction. Someone who wants a masonry heater should choose the form most appealing to them. If you are attracted to big boxes made of bricks, then certainly that is what you should get. But if gentle curves and organic shapes are more appealing to you, you're in luck because masonry heaters can be that, too!

As I explain in Masonry Heaters: Designing, Building and Living with a Piece of the Sun, a masonry heater can be almost any shape. I start with a container that is appealing to the owner-to-be. Then my job is to fill the container with the parts that will turn that appealing form into a living, breathing and warm masonry heater. There is nothing else like it in the world of space heating.

An Heirloom Masonry Heater Part 1

An heirloom is an item one considers valuable and that gets passed on from one generation to the next. It is something that is expected to not only last for several (or indefinite) generations, but which will retain its value through that time. And, though it is not mandatory, often an heirloom is special because it is one-of-a-kind; it is peculiar to one family or household alone.

In my book, Masonry Heaters: Designing, Building and Living with a Piece of the Sun, I introduced the concept of an heirloom masonry heater. I characterize an heirloom heater as a unique heater, designed for a specific house, and designed to be as long lived as possible.

Though masonry construction, by its very nature, is very long lived, it is certainly not indestructible. And masonry heaters in particular are not just your typical masonry construction. They are purposely designed to be subjected to repeated cycles of extreme heat followed by hours of cooling, only to be hit by the extreme heat again. This is very stressful on hard, brittle materials made out of fired clay. These extreme cycles are, or can be, just as destructive as the well-known "freeze-thaw" cycles that masonry can be subjected to in the outdoors.

Heating anything makes it expand. It matters not whether you are talking about something as light as air or as dense as concrete. Heat makes things grow. Something that is heated gets bigger; when it cools, it gets smaller again. What's even worse is when one surface of a material gets substantially hotter than another surface of the same material. The differential expansion - the fact that one part of the same piece of material is expanding faster than other parts - can split a single piece into many pieces. Parts of masonry heaters are subjected to this kind of stress all the time.

The key to making an heirloom heater - one that will last for generations - is to understand how the building blocks of a masonry heater must always expand and contract. "Expand and contract" is the same as "open and close"; "bigger and smaller"; "grow and shrink". This is a lot like the way humans breathe. The chest expands with air, then deflates, expands, contracts. The muscles of the body do the same thing. They flex, then relax, flex, relax. In good heater building, we take note that what these systems have in common is materials of one kind or another that allow them to expand and contract without coming apart. In the case of muscles, the body has connective tissue such as tendons and ligaments that bind the muscle to bone and help hold everything in place as it moves with expansion and contraction. A really good heirloom heater uses those same principles.

Some masonry heaters are just built with common bricks and mortar. These items are quite strong for most purposes in construction. For example, they are very good at bearing lots of weight. But mortar is relatively weak as a connective tissue. It has no flex to it like the tendon of a muscle and not very good marks in tensile strength (the ability to resist tension - a pulling apart stress). So sometimes bricks and mortar will crack when subjected to the stresses of a masonry heater. Well, this is not an issue if the heater is built with some kind of mechanical tendon to hold everything together. But, most bricks are not laid that way. This is why what I call an heirloom masonry heater is not built with common bricks and mortar.

Instead, an heirloom heater is built with refractory (heat resistant) materials. In addition, we bind the heat resistant materials together, literally, with physical tendons that help hold everything together. The materials can expand and contract, but the tendons make sure everything remains where it belongs. This prevents cracks between materials, should they occur, from growing ever larger, which, inevitably, would tear the heater apart. The use of mechanical tendons means we can also use mortars that naturally have a little more "give" or flex than harder mortars. We want the heater to be able stretch and come right back to its original size without doing damage to itself. This is one aspect of an heirloom masonry heater.

Radiant Heat Advantages

When I completed my study for certification in Bau-biologie (Building-biology – the study of how our built living environment affects our health and well-being.) 15 years ago, I had learned that one of the most common causes of illness in the typical home is the presence of mold.

Mold alone can often account for many typical symptoms we might normally consider to be hay fever or just the common cold. Breathing problems, runny noses, coughing, and congestion are some typical complaints that sometimes are a result of the presence and growth of mold. Mold spores, like dust, can float in the air throughout your home.

There are actually very common places where mold often grows even in the homes of folks who take great pride in keeping their houses spic and span. One location is in the drip or evaporation tray at the base of the refrigerator. Another spot is the underside of the water tank portion of a flush toilet. The good news about these locations is that the average person can access these spots and clean up the problem.

But there are potential mold growth areas that are inaccessible. What’s worse is that sometimes the mold growth is encouraged by a forced air or other convection-type heating system. Specifically, mold can be encouraged to flourish in the dark, insulated stud wall cavities of the outside structure of the house.

Convection heat from normal woodstoves or forced air systems does not warm things directly. Instead, it heats air while objects, like the walls of the house, stay colder than the air. At the same time, the excessively warmed air is very low in moisture. But moisture has to go somewhere when it is not in the air. Some of it goes into the walls.

In addition, in most homes heated with a convection system, the outside air is more humid than the inside air. Thus we have moisture in the walls and moist air outside the walls and cold wall surfaces. And what often happens when moist air contacts a cold surface? If you answered “condensation”, go to the head of the class.

The cold, moist conditions created can be a superb environment for cultivating fungi of all sorts. Moist and dark areas like this also are very attractive to insects. The results of moisture in the walls can be as mild as some off odors or irritation and as severe as complete rotting of the wooden structure of the home and serious breathing problems.

By contrast, a masonry heater is not primarily a convection heater. Instead, 80% of its heat energy goes directly via infrared radiation into things. It is heating you, your furniture, your floors, and your walls. The heated items dictate the air temperature. Air temperature and wall temperature tend to be virtually the same.

Since the masonry stove is not superheating air, moisture is not driven out of the room and into your walls. Rather interior humidity levels stay at a higher, healthier, more natural level. At the same time, since wall temperatures are higher, condensation is much less likely from the outside. The end result is a healthier, more comfortable, and more carefree living environment.

Is This a Masonry Heater?

If you visit websites in the United States and Canada for masonry heaters, you are almost guaranteed to find a picture of a Finnish contraflow masonry heater. These are characterized by their tall, upright appearance. Often, they are around seven feet tall. The body of the heater is primarily symmetrical. The loading door and bakeoven door (if equipped) is centered on the mass.

For many people, this is a very pleasing appearance. Many people love symmetry. The Finnish contraflow also has some resemblance to what is commonly thought of as a fireplace in North America. However, all masonry heaters are not Finnish contraflows. What's more, Finnish contraflows lack some versatility.

Note the above picture. Yes, it is a masonry heater. But there definitely nothiing symmetrical about it! Nor is it at all upright. This demonstrates the unique quality of versatility truly available in the masonry heater world. The picture itself is from the website of Creatherm (www.creatherm.de/). I encourage readers to take a look at this website and browse the gallery. You will begin to really appreciate the wide range of possiblities in masonry heaters.