Firewood – Does wood type and storage matter?
Firewood has been gathered for centuries by human beings for cooking and heating needs, though it is primarily gathered for heating in modern times. Wood is a renewable resource when managed properly. There are generally two types of wood in relation to density, hardwoods and softwoods. The main difference in the two types of wood is in their structure. Softwoods are a softer wood whose structure is made to include resin canals, which helps to explain the larger amounts of sap in softwoods. A lot of these trees keep their leaves year-round. Grand Flames service area sees softwoods as the more predominant wood growing in the Colorado Rocky Mountains. Examples of softwoods are Pine, Spruce, Hemlock, Red Cedar and Yew. Hardwoods can be found in some parts of Colorado. Oak, Ash, Walnut and some fruit trees like Cherry are all examples of hardwoods that may or many not be available in Colorado. A general characteristic of these trees is that they usually flower and or lose their leaves at some point in the year. Cottonwoods and Aspens are widely available in Colorado and by characteristic they are considered a hardwood, but for fuel wood purposes they are thought of as a softwood as they are lighter in weight and less dense than “true” hardwoods such as Oak. Elm is similar in this regard as well.
Pound for pound all wood contains the same amount of available BTUs. Although you will get more BTUs from a cord of hardwood than you would from a cord of softwood, simply based on the fact that hardwood is more dense and heavier than softwoods. A BTU or British Thermal Unit is the measure of energy that is required to raise the temperature of one pound of water by one degree Fahrenheit at sea level. Hardwoods are a better option on a cold night as they will burn longer and require less refueling of the appliance. Softwood produces more moderate heat but requires more frequent refueling of the appliance.
The proper seasoning of firewood plays a vital role in both creosote production and efficient heating of the living space. Creosote is the combustible deposit of condensed wood smoke and other organic compounds and is highly flammable. The production of creosote is influenced by wood moisture content, having the proper appliance and venting type, as well as the operation of the appliance. Contrary to popular belief, properly seasoned wood does still produce creosote. Wood that is too dry can have issues as well, such as being consumed too quickly and thus requiring more frequent refueling. This wood can burn more intensely creating temperatures that can lead to “overfiring” and damage to appliance and or the venting system. Grand Flames recommends yearly inspection of the burning appliance and depending on the type of fuel wood and personal burning habits it may be necessary to inspect the system more frequently.
It is widely believed that proper fuel wood moisture is between 15%-25%. The weight of fresh cut logs such as standing live trees, can be made up of 50% water. Depending on wood type and environmental conditions the proper seasoning of fuel wood can take 6-8 months and in some instances 12 months. There are inexpensive moisture meters on the market to help determine the moisture content of wood and they are easy to use.
There are four stages of combustion that must occur in sequence. We will talk only about Stage 1 here, as it is directly related to moisture content in the wood. The first stage is Water Vaporization. Water must be removed from the wood before it is dry enough to begin combustion. It takes large amounts of energy to turn water into steam or vapor. Burning wood that is too wet will send large amounts of energy up and out the flue, wasted energy. Water is great at absorbing the energy from heat. Large amounts of vapor in the flue can cool the combustion gases, slowing down draft and allowing combustion byproducts such as creosote to more readily become attached to the venting system. Burning wood without the proper moisture content can not only create more dangerous conditions within the system but is also a waste of energy and reduces system efficiency.
Federal lands such as Bureau of Land Management (BLM) and the National Forest Service (NFS) may offer very inexpensive fuel wood cutting permits. It does take some labor on your part but is a great form of exercise and a fantastic way to get outside amongst nature. There are also opportunities for someone else to do the work by purchasing cut, split and seasoned wood from providers in your area. And in some cases, they will stack the wood for you as well. Generally, fuel wood is sold and referred to by the cord. A cord of wood is a measurement of stacked wood that is 4 feet high, 8 feet long and 4 feet deep. When possible, fuel wood should be covered to prevent rain and snow from adding moisture to the wood. The seasoning process is helped along by storing the wood in an area that receives good air flow.
Grand Flames believes that fuel wood can be a very efficient and cost-effective way to heat a home. And as mentioned earlier, wood gathering can be a great source of exercise and wonderful opportunity to spend time in nature. And it can be a great family activity, more hands make light work.