Sunday, 16 October 2016

Masonry Stoves

Almost no one enjoys the cold, yet most people in the world live where it is cold for part of the year – even subtropical or Mediterranean climates can get chilly in the winter, and burning deserts can get cold at night. Right now, we keep warm through burning fossil fuels, or from electricity – most of which comes from burning fossil fuels. In the future, however, we can expect billions more people in the world, and far less fossil fuels.

The simplest method of keeping warm, of course, is the oldest one -- fire. Restoring fireplaces to our homes and offices, however, would present a few problems. First, we destroyed most of the world’s forests when we only numbered in the millions, or hundreds of millions, and now there are seven thousand million of us. We could coppice trees (cut them off at the base) or pollard them (cut them at man-height) and let them grow back, and willow grows man-high shoots in a year, but they are suitable only for kindling. Also, fireplaces are spectacularly inefficient; according to author David Lyle, a fireplace and chimney send only 10 percent of its heat to the room, and the other 90 percent goes out into the sky.

There is, however, a little-remembered method that was used in Central and Eastern Europe from the Middle Ages until the beginning of the fossil fuel era – the masonry stove. It relies on a simple concept: it is a hearth surrounded by a thermal mass like cob, brick or tile, which heats up with the fire and slowly releases heat throughout the day. Instead of having a single vertical flue that takes the heat directly into the sky, masonry ovens have a flue that winds around several times before heading outside -- the smoke is typically cold by the time it reaches the outside. All the heat is transferred into the mass, and thence into the room.

Since the initial fire burns fast and hot, it does not generate a great deal of soot to build up inside, and does not need to be cleaned -- although cleaning one would be a much more dificult task, with the internal bends and turns. Fires in masonry ovens do not need to be tended and kept going, as it is not the fire itself that keeps the house warm; thus most oven owners simply set one fire in the morning, and then let the heat radiate through the day. As they release the heat slowly, so they tend to be warm but not hot to the touch – some old Russian ovens were made with spaces on top for people to sleep where it was warm.

Perhaps most importantly, since the ovens need only a brief and quickly-burning fire, they do not require chopped wood for fuel, but can use faster-growing and more common material like straw or the aforementiond willow shoots. The fast-burning fuel would create little soot to build up and block the flue, so their users say they rarely, if ever, require cleaning.

Masonry ovens, like thatched roofs, bale-building and cob, is an old method recently revived when more people began to realize its advantages. Barring any unforeseen complications, millions of people could build sustainable heating systems out of nothing more than clay and stone, and heat themselves with material that is renewable and almost free.

For more information check out David Lyle’s excellent Book of Masonry Stoves, or a recent article on the subject by Low-Tech Magazine. 

Article originally published in 2009. Photo of a German masonry heater, courtesy of Wikicommons. 


Steve Carrow said...

One of the main reasons we bought the home we did here in Wisconsin is that it has a Masonry stove. The builder/original owner called it a russian furnace, and made it out of bricks. It has four long horizontal passes before heading up to the roof, and draws a very good draft. We burn a hot fire with about all the air it wants for complete combustion, and burn for about 3 hours in the evening, then close the damper to keep the heat from continuing out the chimney. In very cold weather, we do another burn in the morning for a couple hours. Overall, we are quite happy with it. We have backup heating options, but my goal is to never have them kick on.

Fireplaces should be made illegal or maybe draw a stiff luxury tax.

Donna OShaughnessy said...

Hello Brian, I just found your blog and so happy I did! We love the masonry stoves we've seen and built a similar thing called a rocket mass stove for our converted grain bin (circular metal grain shed)in Illinois. We ran our stove pipe under a poured concrete floor and just burn our fire 2-3 hrs during the day and the concrete then releases it the next 21 hours or so. It's very cheap to run needing sticks no larger than 2 in diameter. Anyway, love your blog and I'll be back! Please drop by my blog anytime, we're doing similar things on 7 acres.

Brian Kaller said...

Steve, that's great to hear. How long would you estimate the smoke passage is, and how old is it? Can you send pictures?

Donna, I've heard great things about rocket stoves as well. I'll check out your blog -- thanks!

Steve Carrow said...

Brian, the house was built in 1992, but the Russian furnace was not used by the immediate prior owners, so the stove had around seven years of use, was idle, and now we have three years of use on it. The smoke passage is around 25 feet long, and after looking at it more carefully, I realized there are actually five passes before heading up the chimney.

What is best way to send photos? Not sure I can attach to comments here?

Brian Michael said...

Hi Brian,
Loved this story since I had never heard of a masonry stove until I visited Krachow Poland in 2003. There was one in the castle and I asked the guide about it since it was quite beautiful and had never seen one before. She explained to us how it worked and it seemed brilliant to me and very practical!