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How many BTUs in your Yule log? Forester from St. Lawrence County Cooperative Extension explains

Posted 12/22/12

By PAUL HETZLER The tradition of burning the Yule log, or Christmas log, has largely faded away in most parts of the world. Although popularly depicted as a birch log, the original Yule logs back in …

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How many BTUs in your Yule log? Forester from St. Lawrence County Cooperative Extension explains

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By PAUL HETZLER

The tradition of burning the Yule log, or Christmas log, has largely faded away in most parts of the world.

Although popularly depicted as a birch log, the original Yule logs back in 6th- and 7th-century Germany were intended to burn all day without being entirely consumed. While a birch log is picturesque, it doesn’t compare with many other hardwoods in terms of heat value and length of burn. All people are created with equal value; definitely not so with logs.

Heat value, whether it’s 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. Firewood is usually hardwood, though that’s almost a misnomer in as much as some “hardwoods” are softer than many types of softwood. Basswood and cottonwood, for example, have a BTU per (dry) cord rating of around 12 million, lower than white pine (16 million) or balsam (20 million).

As those who heat with wood know, hard maple is the gold standard for firewood, producing a whopping 30 million BTUs per cord. You’d have to burn twice as much butternut or aspen to get the same heat value! Hickory, black locust, white oak and ironwood (or hop hornbeam) come in just behind hard maple. Paper birch has about 20 million BTUs per cord, respectable but not a premium fuel.

Of course there are other considerations besides BTU value in choosing firewood. Even though balsam heats better than butternut, it makes more creosote. Moisture is also critical. When you burn wet wood, 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, doing twice the work compared to burning dry wood—how’s your back these days, anyway?

In the Balkans and parts of southern Europe the Yule log tradition still lives on, while in other regions, including Quebec, a “Yule log” cake is popular for dessert on Christmas.

If you’re one of the few Americans who will be burning 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 to light it with.

But if that’s not your tradition, you can join millions of Americans who tune into the televised Yule Log Program on Christmas. That log apparently not only burns all day, but was first started way back in 1967.

I’d like to know what species of tree it’s from, because with a few of those trees we could lick the energy problem once and for all.

Paul Hetzler is a forester and a horticulture and natural resources educator for Cornell Cooperative Extension of St. Lawrence County.