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Masonry heaters are a great way to heat with wood

September 25th, 2008 · 3 Comments

BY: Norbert Senf, Masonry Heater Association
Energy Focus: Fairbanks Daily News-Miner September 25th, 2008, Section A3

Masonry Heater

Unknown in North America until about 20 years ago, masonry heaters have a long tradition in the colder parts of Europe. Notable exceptions are Britain and France, where our North American fireplace traditions came from.

In a masonry heater, a big charge of wood is burned rapidly, usually 2 hours, and the heat is stored in the large thermal mass, often around 4 tons. Because the wood is burned rapidly, it burns clean and there is no creosote. Emissions are about the same as a pellet stove. Because the heat is stored in a large mass, you get a very steady and cozy radiant heat, with about 100 sq. ft. of vertical radiant panels that run in the 120 deg F – 160 deg F range for a 12 or 24 hour period from one fire.

They were traditionally used as room heaters in Europe, and trying to build one big enough to heat a whole house is a North American idea. Here, we also tend to build them with fire viewing to replace a conventional fireplace in new construction. A masonry heating system often includes an integral bake oven and a heated bench, and sometimes a domestic hot water coil.

It is hard to build one larger than about 20,000 BTU/hr, and gets too expensive. Nevertheless, it makes them a great match for low energy houses, where your average heating load can be 50% that of a conventional house, or less. Even in a less efficient house, they can create a large comfort zone without having to fill the whole house with warm air, first. In some situations, they allow you to be comfortable in a zone of a large inefficient house, without needing large supplies of firewood. At a steady output of 20,000 BTU/hr, you would burn around 3,000 lb of seasoned wood per month. That’s a full cord of dense hardwood, or 1.5 – 2 cords of softwood, depending on the species.

Great, so what’s the downside? Building a masonry heater is a major project. It has to be able to handle the stress of thousands of intense firing cycles and be able to last. So, you can’t cut any corners in building one. The Masonry Heater Association of North America publishes a Plans Portfolio with plans for 7 different heaters that have been tested. The home page also has information on building code issues, and contact information for manufacturers, designers, and professional heater builders, including Alaska.

Cold Climate Housing Research Center in Fairbanks has a large heater in their main lobby that they are actively monitoring. They are also doing ongoing research to determine the suitability of this technology for the Alaskan climate, and to find ways to increase the content of local materials and labor. At heart, it is a very simple technology, utilizing basic materials such as clay and sand. A large portion of the final cost is often imported materials, as well as the mason’s labor to meet aesthetic, safety and building code requirements.

Norbert Senf, of Shawville, Quebec, is the President of the Masonry Heater Association of North America and is considered one of the foremost experts in this field.

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3 responses so far ↓

  • 1 Steven Lefort // Nov 10, 2008 at 1:06 am

    I’m gonna replace a defective outdoor furnace with a masonry heater(within the house) and hope to construct from scratch with local materials (notwithstanding firebrick and special mortar) By trade I’m a cabinetmaker but have done construction and some masonry as well. I’m researching on the web, will buy books, and make contacts to avoid making too many mistakes. Than you very much!!
    Steve Lefort

  • 2 Mastercraft Masonry // Nov 21, 2008 at 10:24 am

    Masonry Heaters are an excellent way to make your home more sustainable and decrease your electric/natural gas usage. We have installed and serviced upwards of 100 units in the Pacific Northwest with many thrilled customers.

    Masonry Heaters can also further decrease your power grid consumption with options such as bakeovens and water heating elements!

    Mastercraft Masonry installs Masonry Heaters designed to our own specifications and extensive quality standards, intent on making these high efficiency fireplaces durable for decades.

    http://mastercraftmasonry.blogspot.com

  • 3 Rob Danielson // Jan 28, 2009 at 10:03 pm

    We included a heater that is very similar to a design specified in Masonry Heater Association of North America plans in our 3,400 sq ft new home and we are very, very happy with it. We’ve not had to augment the heater with any other heat source and its been a very cold winter here in Wisconsin (temps as low as -35F). We’re using less than 1 cord of wood/month– at most two fires a day. The heater may be simple in concept, but I think one would be very lucky to craft a heater that works really well without substantial input from someone who has made quite a few. Ours incorporates quite a few specially cast components. I’d definitely consider attending a Masonry Heater Association of North America workshop. You won’t be sorry when its built though. Our neighbors with outside heaters are amazed at how much less wood we use and how much cleaner our emissions are.

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