Contraflow masonry heaters are the most common type. They are regarded as the most fireplace-like of all the masonry heaters on the market. Contraflow heaters have a raised firebox and a set of down drafting heat-exchange channels that end in a chimney exit at floor level.

Most masonry heaters are designed to utilize wood as their primary fuel. Up to 55 pounds of cord wood can be loaded into the firebox and rapidly burned. If it is burned properly this wood can be turned into 33% combustible solids, 66% combustible gases, and the remaining 1% is ash that can be recycled in the garden. The typical one to two hour burn will slowly heat for a twelve to twenty-four hour period. The faster the wood is burned the cleaner and more efficient it is. When wood is burned slowly it creates pollutants. The gases aren’t completely burned and escape either as wasted heat and smoke or build up in cool chimneys and heat exchange channels as creosote. This inhibits heat absorption, making it much less efficient. These gases will generally burn if the temperature reaches or exceeds 1100 °F.

When building a fire for a masonry heater it is best to place and light the kindling on top. This reduces emissions of atmospheric pollutants. Also using larger pieces of wood provides the best fuel/air ratio; they also give the masonry work more time to absorb the heat from the fire. It is most efficient, for masonry heaters, to have one large fire a day rather than two smaller ones. The more sides of the heater that are exposed to the area you are trying to heat with it, the greater the heater’s efficiency.

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Masonry heaters are highly efficient, producing more heat and less pollution than wood stoves and fireplaces. They have the advantage of being able to store a large amount of heat that slowly seaps into the house for the next eighteen to twenty-four hours. They only need to be fueled once or twice a day. If the fire is burned quickly and with dry wood the build-up in the channels is greatly reduced. Efficiency combustion can reach up to ninety percent. Compared with ten percent for a regular fireplace and sixty for a regular wood stove this is excellent! The heating efficiency is increased even more if the heater is exposed to direct winter sunlight. It will absorb the sun’s warmth and emit it into the room just as it does with fire heat. Along with pleasing asthetics and wonderful heating efficiency, some masonry heaters can include bread ovens, cookstoves, and even waterheating. The biggest problem with this type of heater is that it cannot provied heat quickly from a cold start.

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