How Much Heat Is in that Firewood?

Split into six or eight or ten pieces, each round might last a mid-winter day.

A big (by foothills standards) ponderosa pine blew down several years ago, breaking into two with the top section hung up in some big one-seed juniper trees. I spent a lot of time last winter freeing and getting it onto the ground without killing myself, then cut it into rounds, rolled them down a little hill, split them, and moved them to the house.

In process, I ended up with a lot of juniper too, most of which has been drying through the summer, and I am moving it now. That is a one-seed juniper in the background.

Meanwhile, the butt section of the pine tree, which had been soaked by snow, is now dry, so I finished cutting it up today. (That small chunk next to the saw is from another tree.)

Intuitively, I thought the juniper offered more value as fuel, but it does not come in convenient pieces like pine.

But pine surrenders gracefully to the saw — juniper wants to hurt you. If it can't pinch the chain, its rigid twigs will rip your shirt.

Back in 1913, the eight-year-old US Forest Service was answering that question. "The object of the investigation is to determine the heating values of the woods commonly used for fuel in New Mexico and Arizona, including about 10 different species."

They compared them to coal, since many people burned coal for home-heating back then, and also to "Bakersfield crude oil."

The tests were conducted using a "bomb calorimeter." I would like to own one of those just for the name. ("Professor Murcheson will now demonstrate the bomb calorimeter.")

The big winners were alligator juniper and the bark (not the wood) of Douglas fir, both of them delivering more than 10,000 BTUs per pound, or 76 percent as much per pound as Cerrillos anthracite coal. (The area around Cerrillos and Madrid, N.M., used to produce a lot of coal.)

One-seed juniper was almost as good, 9,900 BTUs/lb., equivalent to 75 percent of Cerrillos anthracite.

Ponderosa pine sapwood produced 8,856 BTUs/lb., while the bark produced 9,275.

Aspen (quakies), incidentally, came in at 8,555. They did not measure Gambel oak, but another source placed it almost as high as the one-seed juniper, which fits what I feel standing next to the stove. Piñon pine, 8,629. Some people would that it burns hotter than ponderosa, which I always thought was true. At least one other site supports me.

Another site calculates heat values in million BTUs per cord, a cord being a tightly stacked pile of wood measuring 4 x 4 x 8 feet. (The method of measurement is not specified.)

Here we see ponderosa pine at 21.7 million BTUs/cord; cottonwood, 16.8; aspen, 18; Douglas fir, 26.5; white fir, 21.1— and they don't measure Gambel oak, one-seed juniper, or Rocky Mountain juniper.

What this means, in the end, is that I will pick up any piece of juniper that is as big around as my wrist.