Some Facts About Firewood

A close-up of a stack of firewood.

Whether for a fireplace, fire pit, or wood-burning stove, the type of firewood you use has a great influence over how well your system performs and how enjoyable an experience you have. Quality, well-seasoned firewood will burn cleaner and more efficiently, while green or wet wood can cause smoking problems, odor problems, rapid creosote buildup, and possibly even dangerous chimney fires.

A few minutes spent understanding firewood will be time well spent, so please read on for general background information, as well as how to buy wood and store wood.

General Background

The heat produced by burning firewood is actually the energy of the sun, the ultimate source of all energy on planet Earth. Through the process of photosynthesis, trees are able to store solar energy as chemical energy that we can use for heat when the sun abandons us in the cold, dark days of winter. Burning wood is just the quick reversal of this process, liberating the suns heat when we need it most.

Unlike the burning of fossil fuels such as gas or oil, burning firewood releases no more harmful greenhouse gases than would be produced were the wood to simply rot on the forest floor.

Seasoned Wood

All firewood contains water. Freshly cut wood can be up to 45% water, while well-seasoned firewood generally has a 20–25 percent moisture content. Well-seasoned firewood is easier to start, produces more heat, and burns cleaner. The important thing to remember is that the water must be gone before the wood will burn.

If your wood is cut 6 months to a year in advance and properly stored, the sun and wind will do the job for free. If you try to burn green wood, however, the heat produced by combustion must dry the wood before it will burn, using up a large percentage of the available energy in the process. This results in less heat delivered to your home and gallons of acidic water in the form of creosote deposited in your chimney.

Wood is composed of bundles of microscopic tubes that were used to transport water from the roots of the tree to the leaves. These tubes will stay full of water for years after a tree is dead.

This is why it is so important to have your firewood cut to length for 6 months or more before you burn it. It gives this water a chance to evaporate since the tube ends are open and the water only has to migrate a foot or two to escape. Splitting the wood helps too by exposing more surface area to the sun and wind but cutting the wood to shorter lengths is of primary importance.

There are a few things you can look for to see if the wood you intend to purchase is seasoned or not. Well-seasoned firewood generally has darkened ends with cracks or splits visible, is relatively lightweight, and makes a clear "clunk" when two pieces are beaten together. Green wood, on the other hand, is very heavy, has fresher-looking ends, and tends to make a dull "thud" when struck.

These clues can fool you, however. By far the best way to make sure your wood is well seasoned is to buy it six or more months before you intend to use it.

Storing Firewood

Even well-seasoned firewood can be ruined by bad storage. Exposed to constant rain or covered in snow, wood will reabsorb large amounts of water, making it unfit to burn and causing it to rot before it can be used. Wood should be stored off the ground if possible and protected from excess moisture when weather threatens.

The ideal situation is a wood shed. You want there to be a roof that protects the wood from moisture but also open or loose sides that provide the air necessary to dry it. The next best thing would be to keep the wood pile in a sunny location and cover it on rainy or snowy days, being sure to remove the covering during fair weather to allow air movement and to avoid trapping ground moisture under the covering.

Also, don't forget that your woodpile also looks like heaven to termites, so it's best to only keep a week or so worth of wood near the house in easy reach. With proper storage, you can turn even the greenest wood into great firewood in six months to a year, and it can be expected to last three or four years.

Buying Firewood

Firewood is generally sold by volume, the most common measure being the cord. Other terms often employed are face cord, rick, or even just a truckload. A standard cord of firewood is 128 cubic feet of wood, generally measured as a pile eight feet long by four feet tall by four feet deep. A face cord is also eight feet long by four feet tall, but it is only as deep as the wood is cut, so a face cord of 16-inch wood actually is only a third of a cord.

A rick is simply a pile, and truck sizes obviously vary tremendously, so it is very important that you get all of this straight with the seller before agreeing on a price; there is much room for misunderstanding.

It is best to have your wood storage area set up in standard 4 or 8-foot increments. Pay the wood seller the extra few dollars often charged to stack the wood, but warn him before he arrives that you will only pay if the wood actually comes out to the agreed amount.

Another thought concerning getting what you pay for is that, although firewood is usually sold by volume, heat production depends on weight. Pound for pound, all wood has approximately the same BTU content, but a cord of seasoned hardwood weighs about twice as much as the same volume of softwood and consequently contains almost twice as much potential heat. If the wood you are buying is not all hardwood, don't pay as much as if it were.

A Few Additional Details

Yes, it's okay to burn a little pine, even construction scraps, as long as you burn just a little and use it mainly for kindling. DO NOT, however, burn large quantities of resinous softwoods, as these fires can quickly get out of hand.

DO NOT burn any construction scraps of treated or painted wood, especially treated wood from decks or landscaping ties. The chemicals used can release dangerous amounts of arsenic and other very toxic compounds into your house.

If the "seasoned wood" you bought turned out to be pretty green and you elected to try to burn it anyway, be sure to have the chimney checked more often than usual, as you may build up creosote very quickly.

You don't have to burn only premium hardwoods. Less dense woods such as elm and even soft maple are abundant and make fine firewood as long as you're willing to make a few extra trips to the woodpile.

On burning artificial logs: convenience is their strong suit and in general they are fine when time is an issue and you want a quick fire without all the muss and fuss of natural firewood. Usually, they should be burned only one at a time and only in an open fireplace. Be careful about poking them and moving them around once they are burning, since they may break up, and the fire may get a bit out of control. Always read the instructions on the package.

A nice campfire in the summer and a roaring fireplace in the winter all have one thing in common, they need firewood. Follow this advice and you're sure to have safe, quality materials.

Reprinted with permission from the Chimney Safety Institute of America,