Everyday Math

Math and the Outdoors

How do you tell the BTUs of a certain type of wood for your woodburner?

There are numerous numbers involved in having a simple woodstove or fireplace. One of the most important is BTU, or the acronym for British Thermal Unit. In a physical sense, 1 BTU is equal to a unit of energy equal to the work done by a 1,000 watts working for 1 hour. When it comes to your fireplace or woodstove, the wood you put into the system has a certain amount of BTUs to keep you warm; some are higher, some lower, depending on the species of tree.

It’s not cut and dry, so to speak. Each tree has not only a certain weight (some are denser than others), but BTUs per cord (a cord is equal to about 128 cubic feet of stacked wood, or about 4 by 4 by 8 feet; it’s interesting to note that only about 70 to 100 cubic feet of a cord is solid wood). A cord is different than a “face cord,” or a pile 4 by 8 feet long and only one “log” (or “stick”) deep.

The following lists some weights/cord and BTUs for some popular “burning woods” (note that the softer woods, such as pines, don’t offer as much in terms of heat energy BTUs; in addition, they do not last as long burning-wise, or burn as hot, as woods with higher BTUs):

  • White ash—3,689 pounds per cord, offers 23.4 BTUs
  • Cherry—3,120 pounds per cord, offers 20 BTUs
  • Norway Pine—2,669 pounds per cord, offers 17.1 BTUs
  • Spruce—2,100 pounds per cord, offers 14.5 BTUs
  • White oak—4,012 pounds per cord, offers 25.7 BTUs
  • White cedar—1,913 pounds per cord, offers 12.2 BTUs
  • Red maple—2,924 pounds per cord, offers 18.7 BTUs
  • Sugar maple—3,757 pounds per cord, offers 24 BTUs


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