What a masonry heater is, and how it heats a house

A masonry heater is not a fireplace and not a wood stove, although it can look like either. It is a heating appliance built on site from firebrick, with a firebox at its heart and a long path of flue channels winding through the masonry around it. The whole thing weighs between one and five tonnes.

The idea is simple. You light one short, very hot fire, usually an hour or two in the morning and perhaps another in the evening. The gases from that fire are led through the channels inside the heater, and on the way they give up their heat to the brick. By the time the smoke reaches the chimney it is comparatively cool, because the heat has stayed in the house. The masonry then radiates that stored warmth slowly and evenly for the next twelve to twenty-four hours, long after the fire is out.

Why the fire is hot and fast

A metal stove is usually run with the air choked down so the fire smoulders for hours. That is what makes smoke, creosote and dirty glass. A masonry heater is run the other way round: the air is wide open and the wood burns fiercely and completely. Combustion efficiency in a well built heater averages around ninety-five percent, and almost no smoke leaves the chimney. Because the burn is so complete, properly built and operated heaters do not build up creosote.

Warm, not hot

Because the heat is spread through so much mass, the outside of a heater is warm to the touch rather than scorching. It is safe to sit against, to lean on and to let children and pets near. The warmth is radiant, like sunshine: it heats the walls, the floor, the furniture and the people, while leaving the air fresh rather than baked. Rooms feel evenly warm from floor to ceiling.

What it can look like

Every heater is designed for its house. The core is always firebrick, but the facing can be ceramic tile (the Kachelofen tradition Udo trained in), natural stone, brick, clay render or lime plaster. Many heaters include a bake oven for bread and pizza, a heated bench, or a cooking surface, and a heater can be connected to a hot water tank.

See masonry heaters built in Canada and Kachelöfen built in Germany and Canada, or get in touch to talk about one for your house.