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Wood - Combustion Heat Values

Combustion of wood and firewood heat values for species like Pine, Elm, Hickory and more.

Type of wood - whether it is hardwood or softwood - burned in the combustion process is important for the heat value and the energy efficiency.

Hardwoods have less resin and burn slower and longer. Softwoods burn quickly. In addition the seasoned length influences on the fuel efficiency. Seasoning the wood refers to the allowed drying time before combustion.

Wood need to be dried at least 4 to 6 months before use.

Densities and heat values of some common wood species are indicated in the table below. Note that the volume of a stack of firewood varies considerably on whether or not it is split and how it is stacked. The moisture content also play a role - the values below are based on a average moisture content of 20%.

For full table - rotate the screen!

Wood - Combustion Heat Values
Wood SpeciesDensity of Dry Wood
(lb/ft3)
Weight of Dry Cord
(lb/cord)
Recoverable Heat Value of Cord
(Dry Wood)
(millions Btu/cord)		Heat Value of Cord
(Green Wood)
(millions Btu/cord)		Units of Green Wood needed to produce 1 Million (cord/Btu's)
Apple 48.7 4100 26.5 18.6 0.054
Ash, white     22.3  
Aspen 27 2290 14.7 10.3 0.097
Balsam Fir 26.3 2240 14.3 10.0 0.10
Basswood 24.8 2110 13.5 9.5 0.106
Beech 44.2 3760 24 16.8 0.060
Birch     21.7    
Black Ash 35.2 2990 19.1 13.4 0.075
Black Spruce 29.2 2480 15.9 11.1 0.090
Box elder 32.9 2800 17.9 12.5 0.080
Buckeye     13.4    
Butternut     15.4    
Catalpa     16.4    
Cherry 36.7 3120 20 14 0.071
Chestnut     12.9    
Coffee tree     21.6    
Cottonwood 24.8 2110 13.5 9.5 0.106
Dogwood     27.0    
Douglas Fir     26.4    
East Hop hornbeam 50.2 4270 27.3 19.1 0.052
Elm 35.9 3050 19.5 13.7 0.073
Hackberry 38.2 3250 20.8 14.6 0.069
Hemlock 29.2 2480 15.9 11.1 0.090
Hickory 50.9 4330 27.7 19.4 0.052
Ironwood     26.0    
Jack Pine 31.4 2670 17.1 12.0 0.084
Larch - Eastern     18.7    
Locust     27.3    
Lodgepole pine     19.3    
Maple     21.6    
Mulberry     25.8    
Norway Pine 31.4 2670 17.1 12.0 0.084
Osage Orange     32.9    
Paper Birch 37.4 3180 20.3 14.2 0.070
Pinon Pine     33.5    
Ponderosa Pine 28 2380 15.2 10.6 0.094
Redcedar - east     19.8    
Red Oak 44.2 3760 24 16.8 0.060
Red Maple 34.4 2920 18.7 13.1 0.076
Spruce     16.0    
Sucamore     19.5    
Sugar Maple 44.2 3760 24 16.8 0.060
Tamarack 38.2 3250 20.8 14.6 0.069
Tanarack pine     21.2    
Yellow Birch 43.4 3690 23.6 16.5 0.061
Yellow pine     22.0    
Walnut - black     21.5    
White Ash 43.4 3690 23.6 16.5 0.061
White Oak 47.2 4010 25.7 18.0 0.056
White Pine 26.3 2240 14.3 10.0 0.100
Willow     13.2    
  • 1 ft (foot) = 0.3048 m
  • 1 lb = 0.4536 kg
  • 1 lb/ft3 = 16.018 kg/m3
  • 1 Btu (British thermal unit) = 1,055.06 J = 107.6 kpm = 2.931x10-4 kWh = 0.252 kcal = 778.16 ft lbf = 1.055x1010 ergs = 252 cal = 0.293 watt hour

Note that in the table above 1 net cord volume = 85 ft3 is used to convert between the "Density" and "Weight of Cord" column (1 stacked cord volume = 128 ft3). Be aware that the densities used for the wood species varies significantly. The densities used above is for natural dried wood where the average moisture content is approximately 20%.

Heat values of cords with dry wood can be estimated by adding 10% to the green wood cords values.

Recoverable heat values are calculated with a stove efficiency of approximately 65%.

How to Calculate the Combustion Heat in MJ/kg from the Table above

  1. calculate "Density of Dry Wood" in kg/m3 by multiplying lb/ft3 with 16.018
  2. calculate "Weight of Dry Wood" in kg/cord by multiplying lb/cord with 0.4536
  3. calculate "Recoverable Heat Value of Cord (Dry Wood)" in MJ/cord by multiplying Millions Btu/cord with 1055.06
  4. calculate "Recoverable Heat Value per kg (Dry Wood)" in MJ/kg by dividing 3 with 2

Example - Red Oak

  1. "Density of Dry Wood" : 44.2 (lb/ft3) 16.018 = = 708 (kg/m3)
  2. "Weight of Dry Wood" :  3760 (lb/cord) 0.4536 = 1705.5 (kg/cord)
  3. "Recoverable Heat Value of Cord (Dry Wood)" : 24.0 (Millions Btu/cord) 1055.06 = 25304 (MJ/cord)
  4. "Recoverable Heat Value per kg (Dry Wood)" : 25304 (MJ/cord) / 1705.5 (kg/cord) = 14.8 (MJ/kg)

The Combustion Process of Burning Wood

  1. Wood heats up to approximately 212 oF (100 oC) evaporating the moisture in it. There is no heating from the wood at this point
  2. Wood solids starts to break down converting the fuel gases (near 575 oF, 300 oC)
  3. From 575 oF to 1100 oF (300 - 600 oC ) the main energy in the wood is released when fuel vapors containing 40% to 60% of the energy burn
  4. After the burning of fuel vapors and the moisture is evaporated, only charcoal remains burning at temperatures higher than 1100o F
  • TC = 5 / 9 (TF - 32)

Related Topics

  • Combustion

    Combustion processes and their efficiency. Boiler house and chimney topics. Properties of fuels like oil, gas, coal and wood and more. Safety valves and tanks.

  • Heating Systems

    Design of heating systems - capacities and design of boilers, pipelines, heat exchangers, expansion systems and more.

  • Material Properties

    Properties of gases, fluids and solids. Densities, specific heats, viscosities and more.

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