|Russian Stove from St Petersburgh Palace|
This excerpt from a blog by Brian Kaller explains why they were used http://restoringmayberry.blogspot.com/2009/02/masonry-stoves.html
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 smoke and heat rise inside insulated ducts which do not conduct heat quickly, interior temperatures rise very high and hydrocarbon gases ignite as they do in a catalytic converter. Makers of masonry stoves claim their products are 85-90 percent efficient.
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 but the thermal mass – 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.
|Image from annebobroffhajal.com|
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 sticks. The fast-burning straw creates little soot to build up and block the flue, so their users say they require little cleaning.
Masonry ovens, like thatched roofs, bale-building and cob, is an old method recently revived when more people began to realize its advantages. If it takes off, 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.