Masonry heaters are clean burning heat storage systems.

Clean Burning
The hotter you burn wood the cleaner it burns. Open fires radiate their heat too quickly. Metal wood stoves restrict air flow to control heat output. These smoldering fires burn the solids in the wood ,but don’t get hot enough to burn the volatiles. The volatiles are combustible gases driven out of the wood as it’s heated. They represent about a third of the energy stored in the wood. Softer woods have a higher percentage of volatiles, hence more unburned fuel is sent up the chimney. This is the soot, creosote, and smoke we associate with wood burning , and the reason we avoid burning the softer wood. Heaters burn wood in an enclosed firebox with lots of air ,enabling clean, hot ,complete combustion. Softwoods that are cheap or free burn best.

Heat Storage
Once the wood is burned the heat is stored in the masonry mass. Also known as a contra flow heater the heated flu gases travel up, and then down again threw interior passage ways, giving up heat to the masonry walls before exiting to the chimney. Even though the fire is only burned for 45 minuets the heat soaked masonry will radiate for up to 24 hours.

Advantages
Metal wood stoves always have a fire burning. It’s not a good practice to leave the house with a fire lit, and the fire tending is continuous. They over heat the air. Overheated air is dry, and rises to the ceiling. Masonry heaters are warm to the touch, but will not burn, especially comforting if you have children around. The radiant heat penetrates the objects in the room including you, while not stratifying the air.

Options
There is a secondary burn chamber in a masonry heater that can have a door added to become a small oven. Depending upon how you fire it, this oven could bake a pizza, or be a slow cooker for cold weather stews.

The contra flow design allows us to run the chimney horizontally, making it possible to separate the chimney from the heater, or add a heated bench.

Outside
We have been doing a lot projects using the heater design outside. It makes a stunning patio heater. The fire is typically burned continuously like a fireplace, but, the heat output is greatly increased, no one has smoke blowing on them, heated benches and tables are possible.