Wood burning for heat has been refined to a science. Highly developed wood stoves and fireplaces are designed to extract the maximum heating capacity of wood. Different woods burn at different rates, and each has its advantages and disadvantages. Understanding the differences in burning characteristics of woods is the first step in correct wood selection.
Contrary to popular belief, pine is suitable to burn. The Jonesy's Woodyard website cites tests showing that seasoned pine produces less creosote than many hardwoods. This is because pine burns hotter and faster than hardwoods, not allowing creosote to build up. Creosote is a thick tar-like substance that builds up on the inside of chimney walls. If allowed to build up, it will catch fire, since it's flammable. The key word is "seasoned." If you burn pine, it has to be thoroughly dry and seasoned, since sap will lead to creosote buildup. Experts at Ontario's Wood Heat Organization point out that pine should be used when heat demand is low, since it burns hotter than other woods but also faster.
Experts concur that oak is an excellent wood for burning. As a hardwood, it burns slow but steady. It is hard to light, so start a small fire with pine first and add larger oak chunks when the fire is burning. Experts further note that all firewood should be thoroughly seasoned before use.
Maple burning characteristics are similar to those of oak. Seasoned maple burns long and slow, making it ideal for fires less tended. The California Energy Commission suggests building a smaller fire with fewer logs, since the burning efficiency is greater than if you built a large smoldering fire with more logs and reduced airflow.
Fir is a softwood, thus it burns hot but faster than oak due to dried pitch in the seasoned sections. The Jonesy's Woodyard site recommends fir if you burn for only short periods, since you will have to feed the fire often. It is not for overnight burning, where a slow but steady burning wood is recommended for long-lasting fires.
Alder has properties similar to those of oak or maple. According to the California Energy Commission, Alder has the highest stored energy of all the woods. For a cord of wood (approximately 2,000 pounds), alder stores about 19 million BTUs of energy. BTU is "British Thermal Units" -- a measure of stored heating capacity. Again, because of the creosote danger, experts state that all wood should be thoroughly seasoned prior to burning.