Wood and Combustion Heat Values

Firewood and combustion heat values - Pine, Elm, Hickory and many more species

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%.

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 4,100 26.5 18.6 0.054
Ash, white     22.3  
Aspen 27 2,290 14.7 10.3 0.097
Balsam Fir 26.3 2,240 14.3 10.0 0.10
Basswood 24.8 2,110 13.5 9.5 0.106
Beech 44.2 3,760 24 16.8 0.060
Birch     21.7    
Black Ash 35.2 2,990 19.1 13.4 0.075
Black Spruce 29.2 2,480 15.9 11.1 0.090
Boxelder 32.9 2,800 17.9 12.5 0.080
Buckeye     13.4    
Butternut     15.4    
Catalpa     16.4    
Cherry 36.7 3,120 20 14 0.071
Chestnut     12.9    
Coffeetree     21.6    
Cottonwood 24.8 2,110 13.5 9.5 0.106
Dogwood     27.0    
Douglas Fir     26.4    
East Hop hornbeam 50.2 4,270 27.3 19.1 0.052
Elm 35.9 3,050 19.5 13.7 0.073
Hackberry 38.2 3,250 20.8 14.6 0.069
Hemlock 29.2 2,480 15.9 11.1 0.090
Hickory 50.9 4,330 27.7 19.4 0.052
Ironwood     26.0    
Jack Pine 31.4 2,670 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 2,670 17.1 12.0 0.084
Osage Orange     32.9    
Paper Birch 37.4 3,180 20.3 14.2 0.070
Pinon Pine     33.5    
Ponderosa Pine 28 2,380 15.2 10.6 0.094
Redcedar - east     19.8    
Red Oak 44.2 3,760 24 16.8 0.060
Red Maple 34.4 2,920 18.7 13.1 0.076
Spruce     16.0    
Sucamore     19.5    
Sugar Maple 44.2 3,760 24 16.8 0.060
Tamarack 38.2 3,250 20.8 14.6 0.069
Tanarack pine     21.2    
Yellow Birch 43.4 3,690 23.6 16.5 0.061
Yellow pine     22.0    
Walnut - black     21.5    
White Ash 43.4 3,690 23.6 16.5 0.061
White Oak 47.2 4,010 25.7 18.0 0.056
White Pine 26.3 2,240 14.3 10.0 0.100
Willow     13.2    
  • 1 ft (foot) = 0.3048 m
  • 1 lb = 0.4536 kg
  • 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 the green wood cords values with approximately 10%.

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

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 burning fuel vapors and evaporated the moisture, only charcoal remains burning at temperatures higher than 1100o F
  • TC = 5/9(TF - 32)

Related Topics

  • Heating - Heating systems - capacity and design of boilers, pipelines, heat exchangers, expansion systems and more
  • Combustion - Boiler house topics - fuels like oil, gas, coal, wood - chimneys, safety valves, tanks - combustion efficiency
  • Material Properties - Material properties - density, heat capacity, viscosity and more - for gases, fluids and solids

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