Masonry woodstoves offer many distinct advantages over metal woodstoves and conventional fireplaces. Today I’ll be taking a look at this masonry combustion system.
First a firebox is built with refractory brick (high temperature brick). This firebox is then surrounded by simple red brick, which provides additional thermal mass. A gap of around 1 inch is provided between the firebox and the outer brick, to allow for thermal expansion.
The flue or venting gas is usually made to zigzag as it passes through the masonry stove. This extends the flame path within the firing space, releasing more heat in the space to be heated. This captures more heat from combustion, and is much more efficient than simply venting all that heat to the outside.
Masonry woodstoves operate at a higher temperature than a conventional metal stove or fireplace. This produces a more complete combustion of fuel, and creates less pollution.
Masonry stoves use the thermal mass of the masonry to store and release heat from burning fuel, so that the heated space is kept warm by thermal radiation long after the fire has died down.
Masonry stoves can also easily incorporate an oven for cooking, which is a very nice feature.
Typically, a masonry woodstove will operate with one large, hot fire per day. The heat from this one fire will usually keep the space warm throughout the day.
Masonry stoves operate most efficiently when air is drawn from the outside to provide oxygen for combustion. This is usually done by drawing in air through the bottom of the stove, where it is pre-heated by the firebox above it; further increasing efficiency. If air is drawn from the inside of the heated area, then heated air is sent up the chimney. This is why an open fireplace is particularly inefficient.
Finally, masonry woodstoves are attractive. The red brick outer layer provides a comforting appearance, and an oven is very inviting, especially if the house smells like fresh baked bread!
Currently I am building my own masonry stove. When it’s done I’ll do another blog entry on this and show some pictures. I used this publication for masonry stove design, and found it very helpful. Lots of good tips and design considerations here.