Not all firewood is created equal. Some species of trees are able to produce much more heat per cord of wood. A cord is the amount of wood in a well-stacked woodpile measuring 4 feet wide by 8 feet long by 4 feet high.
Following are heat values (in million BTUs) per cord for various species of tree. The higher the value, the better the wood.
Ash, Green 22.8
Elm, American 19.8 Difficult to split
Elm, Siberian 20.9 Difficult to split
Locust, Black 28.3 Difficult to split
Maple, Sugar 24.0
Maple, Silver 18.9
Oak, Red 24.0
Oak, Bur 24.9
Oak, Post 25.6
Osage Orange (Hedge) 32.6 Sparks, do not use in open fireplace
Sycamore 19.5 Difficult to split
Walnut, Black 21.8
The Kansas Forest Service has a publication titled “Managing Your Woodland for Firewood” that is quite helpful. See http://www.ksre.ksu.edu/bookstore/pubs/mf773.pdf .
Remember to obtain firewood locally. Emerald Ash Borer is now in Kansas because of transported wood. (Ward Upham)