Over the years many myths have arisen about firewood. Some say that elm is no good. Others say they heat only with maple. Some folks believe that there are woods that can be cut and burnt on the same day. Over my 20 years of heating with wood, I’ve heard a lot of truths, lies and simple confusion. Here are the straight goods. What follows is based on the tree species and winters in Ontario and Quebec. It would also apply to states like New York but if you live elsewhere some adaptation may be required for your situation.
The difference between cutting your own wood and buying it
First of all, there is a world of difference between cutting your own wood and buying it. If you are fortunate enough to have a bush (aka woodlot) with enough trees to provide a steady supply of wood, it will generally be wise to cut out, in order of priority, dead trees that are still sound, dying trees, misshapen and leaning trees and finally trees that are too close together.
In a typical Ontario bush of say ten acres these activities will allow you heat a house entirely with wood forever. It will rarely be necessary to cut a good healthy tree although this may be required some times to make a trail for access or recreation. Done with care, this activity is completely cyclic and the trees should never be depleted. When cutting firewood for yourself note that no mention was made of species. This does not mean that all species are of equal value, far from it, but a tree you already own is the best source of firewood.
If you must or choose to buy firewood, the first unfortunate fact is that it is sold by volume, the most common measure of which is the cord. A cord is a stack four feet wide, four feet high and eight feet long. Firewood blocks are typically 16 inches long so three rows make four feet. Volume (as opposed to weight) is easily measured in the field which is why it is used. It would be far better, if it were not completely impractical, to sell firewood by dry weight.
Here’s why.
Different woods have different densities and different amounts of heat per cord. In addition, a stacked cord of wood necessarily contains quite a bit of air which is useless as a fuel. Obviously, the way firewood is stacked affects how much is in a cord. It turns out that of the 4x4x8 = 128 cubic feet in a “properly stacked” cord about 85 cubic feet is wood and the rest, or 43 cubic feet is air.
The second point is that the amount of water in green wood is quite variable. Elm, for example, contains a lot of water when cut and since some people try to burn it when it is not dry. This may explain why this wood has a bad, but underserved, reputation as firewood.
Some folks burn ash as soon as they cut it on the grounds that “it is almost dry” when cut. Indeed, it contains only seven pounds of water per cubic foot when cut. Ash has a density of 43 pounds per cubic foot when “dry” but this really means it has a 20 per cent moisture content. A 20 per cent moisture content means that if we weigh a block of wood and then dry it in an oven to drive away all the water and then weigh it again the weight of water divided by the dry weight is 20 per cent. If a cubic foot block of ash weighing. In other words, the lore is true, ash is at about 20 per cent moisture when cut!
In general, the dryness of wood is an important factor. Another quick calculation may be illuminating. Elm at 20 per cent is 35 lb. / cubic foot of which 29 lb. is wood and 6 lb. is water. But when it is green it contains 19 lb. of water which is an extra 13 lb. / cubic foot. In a cord of wood there are about 85 cubic feet of actual firewood. So in a cord of wet elm there are 85 x 13 = 1105 lb. of water that would be gone if it were dried to 20 per cent. How much heat does it take to boil this water? It takes about 1000 BTU to boil a pound of water. So the answer is about 1 million BTU so not only would it be very hard to light, about 5 per cent of the elm is wasted in boiling water. For other woods it can be more.
The message is that if you are buying firewood you should prefer dry, dense hardwoods. If you have some time and can buy green hardwood at a discount it might make sense to pile it and dry it yourself. If you are cutting your own wood on your land, this does not apply because you are not paying by volume. Personally I have some areas where I thin out poplar, which has a poor heat value, but it is “free for the labour”, the thinning needs doing anyway, and it is a fine wood for spring and fall.
Be aware that many people use the term “cord” when they mean “face cord”. A “face cord” is not a real measure, but is commonly used to mean 1/3 of a cord. It is more or less one row of blocks four feet by eight feet. If someone talks about a cord, make sure you know whether they are talking about a full cord, also called a bush cord or its tiny brother, the face cord. A full cord generally will not fit in a pickup truck while a face cord usually will.
Cutting firewood
Cutting wood should be part of a plan for a given wooded area. You may find it helpful to walk through your bush when the trees still have leaves and mark those trees that should come out. It is easy to spot a dead tree when all the others have leaves. Likewise, identifying trees as to species is easier then too. I prefer to cut firewood with some snow on the ground. The snow holds the tree off the ground and that way the chainsaw does not hit the earth. It is warm work anyway and should be done when the weather is cool. At the very least, try to cut when the leaves are gone! Much of the sap is pumped to the roots prior to leaf fall and this naturally dries the tree out. As an added bonus, brush which results from the tops of the trees which are too small to burn, is much easier to handle without leaves.
The way you actually cut and collect firewood depends on how much infrastructure you have. Some folks cut lengths in the forest, just about as heavy as they can lift. They carry them out and put them in a pickup truck and then drive them to where they will be cut short and stacked. I prefer to do all the processing except splitting in the forest, so I fell a tree, and cut it up into blocks and then load it into a pickup or trailer and then drive it to where it will be stacked near the house. Then, with a gas-powered splitter, I split and stack. This saves having to move the splitter all over the place and leaves the sawdust in the forest where it belongs. With some species such as ash or poplar splitting with an axe can be faster than using a gasoline splitter! With green elm it certainly isn’t. You will find what works for you. Not only does splitting make pieces small enough to fit in the stove, it makes them stack better and dry faster. Any block bigger than about four inches across should be split.
It is worth being aware of the idea of coppicing, which is generally not practiced in Canada. The practice generally involves cutting a tree down and letting the new growth (suckers) come up from the stump. This growth is usually rapid because the small suckers have the support of a huge root system. Once the suckers are large enough, say 4 inches across, they can be cut and the whole process is started again. Variations involve cutting all but four suckers which are left to grow for a few more years. Then these can be harvested. In an area that has been harvested in the past, you will see evidence of coppicing, generally clumps of trees growing close together.
Storing firewood
Newly cut firewood should be stacked off the ground, in the sun, under cover where the wind can blow through it. Firewood left on the soil does not dry but tends to rot instead. Pallets, gravel, patio slabs or natural rock can all be used to keep firewood off the soil. Cover can be old sheet metal or a tarp so long as rain does not fall on the wood. Wood stacked in a forest does not dry very well. If you are going to do a lot of heating with wood it may be worth building a firewood shed with open walls or perhaps with just solid ends to allow ventilation. If it is near where the firewood will be burnt this will prove convenient especially when there is snow on the ground. I had a nice pile of firewood once about 300 metres from the house, thinking I would move it when I needed it. We got three feet of snow and it sat there until spring because I could not get to it.
How long to dry firewood is an ongoing question. If you can get your firewood stacked by March here, by September it is generally usable. Prior to burning it, bring it into the house for a week or more where it will help humidify the house and lose any surface moisture. Two-year-old firewood is perhaps a bit better. Don’t let it get too old though, or it will eventually rot.
How much firewood do I need?
This topic has resulted in tons of confusion! I have heard folks tell me that they heat the whole house with two face cords a year. Then I go and visit them and discover they have an oil furnace and electric baseboard heaters! My house is old, drafty and large. I burn about six full cords of good hardwood per year. I keep saying that things depend on other things, but it really is true. This list shows factors which influence how much wood you will need. For your first year, talk to neighbours, make a guess and double it — best not to run out and any excess can be burnt the following year.
Factors to consider when deciding how much firewood to buy/split:
- more firewood OR less firewood
- colder weather OR warmer weather
- house at 22C OR house at 18C
- low density wood OR high density wood
- badly insulated house OR well insulated house
- drafty house OR tightly sealed house
- inefficient stove OR efficient stove
- sole heating method OR just a supplement
Stove volumes are finite
The fire box in a stove or furnace is only so big. Long burn times are desirable especially overnight or when you have to go away for a day. The more BTUs you can put in a firebox, the longer the burn time assuming that the air supply is controlled. This is an argument for high density wood for such occasions. Because my firewood contains a mixture of species, I find it convenient to simply set aside larger maple or ironwood blocks for times when I need a long burn. During the day, or when I am sitting by the stove it is no trouble to put in faster burning wood say every hour, but I don’t want to have to get up at night.
Creosote and other nasties
Creosote is a black flaky or gummy material that can result from combustion. In an ideal world wood burns to CO2 and water. In practice there are many products of partial or incomplete combustion. These products include creosote and soot, both of which can contribute to chimney fires. There is a debate about whether some woods produce more creosote than others. My advice is not to worry about it. This does not mean ignore it! Inspect your chimney now and again and clean it when it needs it. I like to clean my chimney at the end of every burning season and that way it is ready to go when the cold weather comes again. It is also a chance to inspect the flue with enough time to repair it if there is a problem. It is no good to clean it in October only to discover a problem that could have been fixed when the weather was warm.
Treated lumber and similar products should be avoided completely. There have been different chemicals applied over the years to prevent wood from rotting including copper, chromium and arsenic. You don’t want to sprinkle your land with these heavy metals, nor do you and your neighbours want to breathe them. Old railroad tires are similarly to be avoided. Do not burn painted wood either.
Some people burn pallets since they are often given away. Generally, the wood from them is fine to burn but it is far from effortless as the pallets must be cut up in order to fit in a stove. Most people find the labour more than the wood is worth.
Summary
Wood, whether you cut it or buy it costs you labour, cash or both. Burning wood is more effort and messier than burning oil or natural gas but it is completely renewable and much more environmentally sane. The CO2 released during burning is that which was taken out of the atmosphere by the growing tree. If you do not deplete your wood lot, it is almost carbon neutral (for more on this, see Dan Needle’s article, this issue). It can also save you a lot of money. My heating cost is about $300 per year which goes on gasoline to run a chain saw, chain oil, and bars and chains for the saw. Added bonus: you won’t have to buy a gym membership.
- Peter Sibbald