Anybody who works with wood on any level, or for any purpose understands the importance that moisture can play where wood is concerned. Thus, the need for a high quality moisture meter. If you’re in the market for one (and if you work with wood, either for wood crafting projects, or say, if you use wood as fuel in a fire place or wood burning stove, then you should be), we’ll outline the different options available to you in broad terms, just below, so that you can make the right choice for you.
Before we do that, however, there’s one term you need to know: EMC, or Equilibrium Moisture Content. Simply put, this is the point at which a given piece of wood is neither gaining nor losing moisture, and as such, it makes a good baseline. Of course, this is going to be dependent on the season you’re currently in, the amount of average rainfall in your area, the average humidity, and other factors, but it’s pretty easy to find the baseline. To do that, you simply hang thin strips of whatever type (species) of wood you commonly work with in your home, in the area where you work with it (or, in the case of a wood burning stove or fireplace, you’ll hang these species strips in the area where you store your fuel). Then, it’s simply a matter of taking a daily reading over a period of time and averaging the results. The only other thing to know by way of background information is that wood is a pretty good electrical insulator, meaning that it is not terribly conductive, and water is highly electrically conductive.
As to the meters themselves, they come in two basic flavors. Pin-Meters, and Pinless Meters. We’ll discuss both types in brief below.
Pinless Moisture Meters
These operate on the principle of capacitance, which is a fancy way of saying that these devices compare the relationship of the wood’s electrical properties and the water (moisture content) that wood contains. Capacitance simply refers to the ability of a given object to hold an electrical charge. Earlier, we said that wood was generally not very good at this (low capacitance) while water is very good at it.
Pinless meters have a couple of significant drawbacks to be aware of, however. The big one is that they cannot tell the difference between core moisture, that is, moisture toward the center of the given piece of wood, and shell or surface moisture. This can be problematic if you’re burning wood for fuel, but is much better suited for wood planks and other, thinner pieces that woodworkers would likely make use of. The Pinless Wood Moisture Meter is also excellent at determining the average level of moisture in a large, three-dimensional space, so again, it mostly depends on what you need it for. Woodworkers will likely gravitate toward this type, while people who burn wood for fuel wouldn’t find it terribly useful.
These wood moisture meters come equipped with metal prongs (usually two of them) built onto the end of the device. These pointed prongs are inserted into the wood in question, and a reading taken. The strongest selling point of these types of moisture meters is the fact that it provides good, fairly accurate information about the moisture content overall (core and shell), and these types of devices are ideally suited for people who are using wood as a source of fuel. On the other hand, the thing that makes Pin Meters so useful to those who burn wood makes it less useful to woodworkers. Namely, the presence of those pins. Woodworkers generally like the wood they work with to be unblemished, which is impossible if you’re having to gouge the wood to insert the pins just to check your moisture level. Again, it’s going to depend on how you’re using your wood as to which specific type of Moisture Meter will best serve your needs.
In many parts of the US, about the best you can hope for where letting wood dry naturally is 15%. For finished pieces of furniture, woodworkers like to see a moisture content no higher than 6-8%, and again, this is important, because as you know, wood expands or contracts, depending on how much moisture it actually contains. If you want to build a solid, tightly constructed piece of furniture, you need to be using dry wood. If you start a project using wood with a relatively high moisture content, then when the wood dries out, your piece won’t fit together as well as it could, because the wood will contract slightly as the piece dries.
People who burn wood for fuel obviously don’t care about that, but they face other potential problems. The largest of these is the fact that the higher the moisture content a given fuel log has, the less heat and the more smoke it will produce. If you’re using wood for fuel, obviously this is a big consideration, because the more heat you can get out of each fuel log, the less fuel you’ll actually wind up using. The smoke problem is a rather insidious one, because smoke can back-fill into the room you’re trying to heat, causing all sorts of problems and is generally a pain to have to try and clean later.
The other, and potentially worse problem with excessive smoke is that it can create a buildup in your stove. This buildup is not only unsightly, but the residue itself is flammable, and the more of it that builds up, the more likely you are to have an uncontrolled fire. Many, many people have inadvertently burned their homes down simply by doing nothing more than burning wood with a moisture content that was too high. Where wood for fuel is concerned, you should never burn anything with more than a 25% moisture content, and the lower you can get that number, the better!
The bottom line is, no matter how you use the wood you work with, whether it’s to make furniture or do other types of projects, or to burn it for fuel, a Wood Moisture Meter is a good investment. They’re relatively inexpensive, and should be considered a must-have addition to your tool kit.