What many here still do not realize is that you receive a million BTUs of heat from 134 lb of firewood, regardless of what tree produced it: poplar, cottonwood, oak or hickory. I tried to convince one of my customers last year to try red elm but he refused. All he wanted was ash, oak, hard maple, and walnut. This year he finally agreed to try it and said, "That red elm you brought last time is really good firewood. Thanks for finding it. Do you have any left?"
Guess what. I'm sold out of red elm and it's really rare and tough to find. Not many of these trees remain.