Modern Heating Using Old World Technology
An arm full of cordwood firewood burned in a masonry heater can heat a house for 12 or more hours. Another bonus is that it will produce a spectacular flame that the family gets to enjoy through a ceramic glass window. People feel a sense of security and comfort from an attractive fire that gives warmth to the home. Due to advancements in air sealing, insulation materials, and building practices today’s homes require far less BTU’s and homes don’t have to be tiny to be well heated. Wood-fired appliances have been under scrutiny for air pollution. However, in terms of carbon emissions and air quality, the high fire temperatures in a masonry heater will burn off all the hydrocarbons. Tests have shown the emissions of masonry heaters are equal to, or better than most wood-fired heating appliances. Masonry heaters don’t require electricity to operate. If there is a loss of power, you don’t lose the ability to heat your home. Masonry heaters offer a natural beauty and warmth that is matched by nothing else in the home and because of their mass, they become the focal point of the room.
A masonry heater has a high efficiency and an air controlled firebox that burns cordwood (firewood) in two to three hours. The heat is absorbed into the mass (masonry) as stored heat from the short hot fire and is then released slowly over the next 12-24 hours. Masonry heaters can weigh 1,760 pounds at their smallest, and exceed 10,000 pounds for a large heater. The firebox can be sized to accommodate cordwood of 10 inches to 20 inches in length and the flue channels are determined by the size of the firebox. The surface temperatures of the exterior of the heater are around 150 °F, and don’t exceed 230 °F. The heat charged mass radiates heat to gently warm objects and people in the room at relatively constant and comfortable temperatures.
Different Styles of Heaters and Building Materials
Masonry heaters have, and are currently built throughout various parts of the world. Early designs can be traced to ancient China, Korea and Rome. Materials and styles have varied results. In different areas of Northern Europe and Asia, heaters can be referred to as: stoves, heaters, or ovens. Masonry heaters can be made from common brick, fire brick or cast refractory and can be clad or veneered in stone, tile or common brick. Special refractory material can be precast to make the whole inner core, or in combination with modular firebrick.
Laboratories throughout North America and Europe are conducting research on combustion efficiency and emissions. This has resulted in advancements in more complete combustion in the firebox, matched fireboxes and dimensioned flue channels, and hardware used. Doors are designed to let in just the right amount of air into the firebox, and in precisely the right places to ensure complete combustion. This attention to detail, yields the most heating benefits from firewood, with the least possible emissions and highest efficiency.
One of the most common heaters is the Finnish contra flow, designed so the flue gas takes a 90 ° turn before exiting the heater. In recent years the bell style heater, which uses multiple chambers, known as bells, are used to slow the hot gases before they exit the chimney. The see-thru masonry heater, with large glass doors on opposite sides of the heater, was developed in North America. No matter what type of heater is built, most can have a bake oven built into it. The bake oven is integrated into the flue system and can be independently fired (direct fire) or can be placed in the flue path, but not vented (indirectly fired). Some are large enough to bake a large pizza, a holiday turkey or artisan bread.
Brick and firebrick are the most commonly used materials, as it is so readily available. And limestone, sandstone and Granite are all good choices for the veneered exterior. Soapstone is also an excellent material for masonry heaters, inside and out. This is due to soapstone’s unique qualities of density and specific heat capacity which gives it exceptional ability to absorb and store heat. Another type of material used in masonry heaters is tile. These heaters or “kachelofens” are found in Northern Europe, and Eastern Asia.
Masonry Wood Fired Bake Ovens
If you’ve been to Italy or France you’ll know that wood fired pizza and bread ovens are as common there, as backyard charcoal grills are, in North America. When properly built with masonry materials, these ovens can achieve a 600-750 °F hearth temperature and 900-1000 °F dome temperature. This combination of conductive heat on the hearth and radiant heat from the dome, provide the essential conditions for baking the perfect Neapolitan pizza in a few minutes
Pizza oven hearths can range in size between 24” and 72” in dome shapes. If you need to feed a large crowd, these ovens can handle it. Ovens can be built in various styles with a very attractive in appearance.
Artisan bread bakers have rediscovered the qualities of wood fired ovens and many professional bakers choose the low vault style. This low ceiling allows the steam to envelope the loaves of bread quicker which makes the loaves crust shiny and crispy. These ovens range in size from three to four feet wide by five to seven feet long. With wall mass of up to 12 inches thick and plenty of insulation to hold the charge needed to do several full loads of bread.
Ovens are being built in community gardens, churches and parks. Very often ovens are built in collaboration with local food banks for people to get together and pool their energy and to pass on old traditions of creating good bread. Ovens can also be used for roasting everything from fire roasted tomatoes to seared and roasted fish, pork and beef.
As with masonry heaters, hardware varies depending on need. A backyard oven could get by with a sheet metal clad wood door whereas commercial bread ovens may have a line of insulated stainless steel and counter balanced doors for easy access and efficient loading.
Ovens can be built with materials as basic as cob (clay, sand and straw), firebrick or castable refractory cement. Precast and extruded clay kits are available for home sized ovens and some commercial ovens. Larger low vault commercial ovens are generally made from firebrick. Exterior finishes include: plaster stucco on block or brick, stone and tile.
Masonry Heater Association of North America
The Masonry Heater Association of North America is a non-profit association dedicated to serving the interests of the masonry heating industry and its clients. It was started in 1987 as the outgrowth of an ASTM Task Group on Masonry Heaters.
MHA offers certification to builders who strive for quality and professionalism. Certified builders are required to pass a written exam, display a level of competence in masonry skills through a practical exam and submitted work projects.
“MHA is an association of builders, manufacturers and retailers of masonry heaters and masonry wood fired bake ovens whose purpose is to promote the industry, sponsor research and development, shape regulations, standards and codes, inform and educate the public, and further the expertise and professionalism of its membership.”
MHA’s Annual Meeting at Wildacres Retreat
Every spring, around mid-April, some of the most knowledgeable people associated with masonry heaters and bake ovens in the world, gather for a full week at Wildacres Retreat, in the great Blue Ridge Mountains of North Carolina. MHA members, old and new, along with invited guest, gather to meet, build and exchange Ideas. Expert guest speakers from within, and outside the organization, present information to the membership about: Design, Materials, Regulations, Building Science, and other relevant issues. Throughout the week, multiple masonry heater and bake oven “hands on” building projects are started for education and testing. The week culminates, when bake ovens, masonry heaters and smokers are all fired up and used in a fiesta. Pizza, crepes, vegetables, smoked cheeses, and meats, are all cooked in the bake ovens and enjoyed by our expert members and guest alike. The feast of good food, music and dancing goes on into the evening and the week goes by much too quickly.
The MHA annual meeting is a one-of-a-kind event and available only to MHA members. Registration begins around the first of the year. Space is limited and fills up. Keep going to the MHA website (www.mha-net.org) and watch for the annual meeting information.
The Masonry Heater Association invites masons to consider joining the association. Our members are very welcoming and willing to share their knowledge to the betterment of the industry.
Words and Photos: Richard Smith