What is a good heating stove?

• It is a slow combustion heater to build a controlled fire in.
• A good fireplace or stove holds on to the heat, letting it escape out instead of letting it fly up the chimney.
• Technically a slow combustion heater is both a combustion changer and a
  heat exchanger.
• It burns the wood efficiently and gets the heat into the house.

How big a stove or fireplace do I need?

It depends on:

• The size of your house/room
• The insulation of your house
• The design of your house
• Your desire for the pleasure of the flames or the heat
  
  

The European rule of the thumb is 60-70 watt per sqm. by a height of 2,4m from the floor to the ceiling.  

Efficiency

The most important factors in terms of efficiency are:

• The air tightness of the stove
• The amount of radiating surface
• The type and dryness of wood
• The house insulation
• The way the stove is controlled  

An efficient stove will burn the wood slowly rather than in a flash. Burning is controlled by regulating the flow of air into the firebox.

Wood burns in three phases:

• Water evaporates
• Wood turns into charcoal and gases
• The charcoal burns

Many stoves lets the gases go up the chimney unburned. These gases can represent 60% of the potential heat of the wood. To avoid this the stoves require oxygen mixed with the gases at a temperature of at least 350 to 600oC. Some stoves have designs that brings secondary air to the combustion chamber to burn gases and particles that would normally go up the chimney unburned and by that they get a higher efficiency. A slow combustion heater is normally driven by primary air. By implementing secondary air you will burn gases and particles more efficiently at a lower temperature in the firebox. This is normally called Clean Burn technology and will increase the efficiency by almost 40%.

To obtain high efficiency the wood has to be dry. Wet wood will in addition to generating less energy create creosote in the chimney when the combustion is incomplete.

• 1 Kg wood has approx 3800 W energy content (100 % efficiency)
• 1 Kg wood gives you approx 420 W (12 % efficiency) burned in an open fireplace
• 1 Kg wood gives you approx 1900 W (50 % efficiency) burned on a traditional fireplace 
• 1 Kg wood gives you approx 2800 W (75 % efficiency) burned on a clean burning fireplace
  

How much energy you get from the fuel depends on the moisture content. Ideal fuel moisture is 20 % which gives you approx. 2800 W per kg with an 75 %  efficiency.

 

Dry wood gives you more heat per kg, but shorter burn time