1632 



Canadian Forestry Journal, April, 1918 



The Fuel Value of Wood 



By W. B. Campbell 



Forest Products Laboratories of Canada, March 12, 1918. 



An Authoritative Guide for the Wood User, 

 Giving Accurate Data on Fuel Values. 



Owing to the scarcity of coal 

 in the winter just passed 1917- 

 18; many people are becoming more 

 interested than heretofore in the 

 use of wood as fuel. It is the 

 purpose of this short article to 

 discuss the value of different woods 

 in this connection. 



The primary quality of a fuel 

 is to give off heat when burned. 

 Secondary qualities are ease of hand- 

 ling, ease of kindling, amount of 

 ash, etc. From a chemical point 

 of view, the burning of a substance 

 in air simply means the combining 

 of that substance with the oxygen 

 of the air. This reaction liberates 

 heat in a greater or lesser amount 

 depending on the substance burned. 

 The amount of this heat is measurable 

 and the unit used for practical 

 purposes in this country is what 

 is known as the British Thermal 

 Unit or more familiarly as the B. 

 T.U. One B.T.U. represents the 

 amount of heat necessary to raise 

 the temperature of one pound of 

 water through 1 degree Fahrenheit. 



For every combustible substance 

 there is a corresponding "Heat of 

 Combustion" which is invariable for 

 that substance and is expressed as 

 the number of heat units or B. 

 T.U's. given off by the combustion 

 of 1 pound. This quantity is the 

 same no matter how slowly or how 

 rapidly the combustion takes place 

 and it has no direct reference to 

 the temperature of the fire. If com- 

 bustion is rapid a large number 

 of heat units are produced in a 

 short time and consequently the 

 temperature is high. If combustion 

 is slow the number of heat units 

 per second is small and the heat 

 gets a chance to become dissipated, 

 consequently the temperature is low 



When Wood is Wet 



If a fuel is wet the water must 

 all be evaporated during the burn- 

 ing of the fuel and this takes away 

 some of the heat. To heat up 

 a pound of water from the ordinary 

 temperature to the boiling point, 

 evaporate it and heat the steam 

 to the temperature of the chimney 

 gases requires about 1220 B.T.U. 

 Consequently for every pound of 

 water in the fuel, this amount of 

 heat goes up the chimney. This 

 loss is present to a greater or lesser 

 extent with all fuels but is par- 

 ticularly important with wood. 

 Coal may contain 2 or 3 per cent, 

 water or 40 to 60 pounds per ton. 

 Green wood may contain 1,500 to 

 2,000 pounds of water per cord. 

 Air dried hardwood holds about 

 720 pounds per cord. The reason 

 for demanding well dried wood is 

 therefore quite obvious. 



Why Woods Differ 

 The next statements may not 

 seem quite so evident but they 

 are equally true. The "Heat of 

 Combustion" or "Calorific value" 

 is, within narrow limits, the same 

 for all woods. That is, a pound 

 of one wood will give off almost 

 exactly the same amount of heat 

 as a pound of a difTerent wood. 

 This does not mean that a cord 

 of one wood will give the same heat 

 as a cord of any other wood because 

 one cord may be much heavier 

 than the other. Some woods are 

 highly resinous — red pine, for in- 

 stance—and these have a slightly 

 higher heating value on this account 

 but the difference is not great. 

 The reason for all woods having 

 equal Calorific Values is not far 

 to seek. Fundamentally, all woods 



