Firewood Types: BTU per Cord for 20 Woods, Best to Worst

The best type of firewood is the densest dry hardwood you can get: black locust, hickory, oak, beech, sugar maple or ash. Virginia Tech's Brian Bond and Adam Downing give these figures for a cord at 20% moisture content, in million BTU:

• Black locust - 29.3 (4,200 lb per cord)
• Hickory - 27.7 (4,327 lb)
• Black birch - 26.8
• White oak - 26.5
• Apple - 26.5
• Beech - 24
• Hard maple - 24
• Red oak - 24
• White ash - 23.6
• Hackberry - 20.8
• Paper birch - 20.3
• American elm - 20.2
• Sycamore - 20.2
• Black cherry - 19.9
• Soft maple - 18.7
• Hemlock - 15.9
• Aspen - 14.7
• White pine - 14.3
• Basswood - 13.5
• Cottonwood - 13.5 (2,108 lb)

A cord of black locust holds more than twice the heat of a cord of cottonwood.

Virginia Tech's figures rest on one fact: the heating value per oven-dry pound is about 8,000 to 9,500 BTU for all species. A cord of dense wood simply contains more pounds. The South Yorkshire Firewood guide puts it the same way: hardwoods are generally denser than softwoods, so they burn longer and produce more heat, and being less resinous they leave less tar in the flue. Softwood's resin makes it useful as kindling.

The Virginia Tech notes also describe the three stages of burning: the wood dries and ignites up to about 500 °F; from 500 to 1,100 °F it releases flammable gases that hold more than half its energy; above 1,100 °F the remaining charcoal burns. Wet wood spends its energy in the first stage boiling off water.

Heat is not the only measure. The South Yorkshire Firewood table and Forge and Flame's guide add smoke, sparks and smell:

• Ash - rated one of the best; it has low moisture even when green.
• Oak - one of the best, but very dense and can take up to 2 years to season.
• Beech - burns well but sparks and needs long seasoning.
• Birch - lights easily and burns fast.
• Hickory - very high heat with a strong, earthy aroma (Forge and Flame).
• Apple, cherry and pear - pleasant smell and little spitting (South Yorkshire Firewood); Forge and Flame lists cherry, apple and yew among the best-smelling firewoods.
• Horse chestnut and sweet chestnut - spit and throw sparks, poor on an open fire.
• Pine and larch - spit and leave soot deposits; pine makes good kindling. Spruce is rated low quality.
• Poplar - black smoke even when seasoned.
• Alder, elder, willow - burn fast with little heat, or need very long seasoning.

The worst thing to burn is not a species at all. The US EPA says never burn painted, coated or pressure-treated wood, plywood, particleboard, ocean driftwood, wet or rotted wood, or household trash, and it lists plastics, foam and colored-ink paper among the household trash to keep out of the stove.

Freshly cut wood is usually above 60% moisture for most hardwoods and over 100% for some species (Virginia Tech, oven-dry basis). The US EPA says wood burns best below 20% and should be seasoned at least six months; Virginia Tech says it takes about 9 to 12 months in most locations to air-dry from green to 20%. Kilns are faster: green firewood can go from 52% to 20% in 30 hours at 220 °F.

Virginia Tech notes that splitting speeds drying because it exposes more wood surface. EPA's storage advice is to keep wood outdoors, off the ground, with only the top covered, since covering the sides traps moisture. Test with a moisture meter before you burn. Forge and Flame adds the visual signs of dry wood: darker color, cracks in the ends and a hollow sound when struck.

A standard cord is stacked wood plus air filling 4 by 4 by 8 feet, 128 cubic feet. Virginia Tech notes studies have found the solid wood in that space ranges from 58 to 94 cubic feet depending on how tightly it is packed and how straight and thick the pieces are. Face cord, rick, pile and truckload are not standardized; a truckload measured anywhere from under 1/5 cord to slightly over 1/2 cord in the trucks studied.

The appliance matters as much as the wood. Virginia Tech gives open fireplaces 10 to 15% efficiency, modern wood stoves 75 to 80%, and masonry stoves 80 to 95%.

Split firewood loses its leaves, so bark and end grain are what you have to go on. Our white ash, hickory, black locust, red oak and white oak pages show the end grain, and WoodLens can identify a split or a round from a photo.

Virginia Tech's advice is not to move firewood, because it spreads Asian longhorned beetle, emerald ash borer and thousand cankers disease; check with your state forestry agency for restrictions.