Even among the hardwoods, some burn hotter than others, churning up more BTUs per cord. For the sake of comparison, here are the BTUs per cord of some of the hardwoods commonly found in the eastern United States:
Osage orange, 32.9 BTUs per cord
Shagbark hickory, 27.7 BTUs per cord
Eastern hornbeam, 27.1 BTUs per cord
Black birch, 26.8 BTUs per cord
Black locust, 26.8 BTUs per cord
Blue beech, 26.8 BTUs per cord
Ironwood, 26.8 BTUs per cord
Bitternut hickory, 26.5 BTUs per cord
Honey locust, 26.5 BTUs per cord
Apple, 25.8 BTUs per cord
Mulberry, 25.7 BTUs per cord
Beech, 24 BTUs per cord
Northern red oak, 24 BTUs per cord
Sugar maple, 24 BTUs per cord
White oak, 24 BTUs per cord
White ash, 23.6 BTUs per cord
Yellow birch, 21.8 BTUs per cord
Red elm, 21.6 BTUs per cord
Hackberry, 20.8 BTUs per cord
Kentucky coffee tree, 20.8 BTUs per cord
Gray birch, 20.3 BTUs per cord
Paper birch, 20.3 BTUs per cord
White birch, 20.2 BTUs per cord
Black walnut, 20 BTUs per cord
Cherry, 20 BTUs per cord
Green ash, 19.9 BTUs per cord
Black cherry, 19.5 BTUs per cord
American elm, 19.5 BTUs per cord
White elm, 19.5 BTUs per cord
Sycamore, 19.1 BTUs per cord
Black ash, 18.7 BTUs per cord
Red maple, 18.1 BTUs per cord