The tradition of burning a Yule or Christmas log has largely fizzled out in most parts of the world. Although often depicted as a modest-size birch log, the monster Yule logs back in 6th and 7th century Germany were tree trunks that were intended to burn all day, in some cultures for twelve days, without being entirely consumed. It was important that an unburned portion of the log remained after the marathon Yule-burn, because this insured good luck in the upcoming year. The Yule remnant was tucked away in a safe place inside the home (presumably after it was extinguished) and was used to light the following year’s Yule log.
While a birch log is picturesque, it doesn’t compare with many other hardwoods in terms of heat value and how long it will burn. All people are created with equal value; with logs, not so much.
Heat value, whether from coal, oil or wood, is measured in BTUs, or British thermal units. One BTU represents the energy required to heat a pound of water one degree Fahrenheit. As most people in this part of the country know that fuel wood is usually some type of hardwood, that is a misnomer. Certain hardwoods are actually softer than softwoods, or conifers. Basswood and eastern cottonwood, for example, have a BTU rating per dry cord of around 12 million, lower than that of white pine (16 million) and balsam (20 million).
As those who heat with wood know, hickory, hard maple, and black locust are tops for firewood, producing almost 30 million BTUs (mBTU) per cord. You’d have to burn twice as much butternut or aspen to get the same amount of heat! Sources fuel vary in their evaluation of fuel woods, but beech, white oak and ironwood (hop hornbeam) rate quite high, around 25 mBTU/ cord. The iconic paper birch has about 20, respectable but not a premium fuel.
Of course there are other considerations aside from BTU value in choosing firewood. Even though balsam heats better than butternut, it throws a lot of sparks as it burns, creating a potential hazard in an open-hearth fireplace. Moisture is also critical. Well, critical not to have it. When wet wood is burned, much of the wood’s heat value goes into boiling off the water. Fresh-cut elm is 70 percent water by weight—you’d get very little heat from that, assuming you could even keep it lit.
Outdoor furnaces, because they have a blower, are capable of burning green wood. This might be seen as a convenience, but if you burn unseasoned wood in an outdoor furnace you’re spending twice as much time, lifting twice the amount of wood compared to burning dry fuel. (How’s your back these days, anyway?)
In the Balkans and parts of southern Europe the genuine Yule-log tradition still lives on, while in other regions, including Quebec, a “Yule log” cake or bûche de Noël is a popular dessert at Christmas time. If you’re one of the few Americans who will burn an actual Yule log in an open hearth this year, you probably have a good chunk of dry hard maple or hickory set aside, plus a remnant of last year’s log with which to light it.
But if that’s not your tradition, you can join millions of Americans who tune into televised Yule Log Programs this holiday season. While there are many from which to choose these days, the original made its first appearance way back in 1967. Not only does that log appear to burn indefinitely, it was lit fifty years ago. I’d like to know what species of tree it’s from, because with just a few of those we could solve the energy problem once and for all.