What are wood moisture meters?
A wood moisture meter is a hand-held device—either analog or digital—that measures the moisture content in wood. Moisture meters are used by woodworkers, furniture makers, wood flooring installers, and others who work with wood in order to ensure the quality of their wood craftsmanship.
Why is wood moisture content so important?
Wood moisture content is important because wood shrinks as it loses moisture and swells as it gains moisture. This happens because wood is hygroscopic. This is a fancy way of saying that wood is continuously absorbing moisture from the environment and releasing moisture back into the environment. Here’s how this works…
If you put a piece of wood with low moisture content into a humid environment, it will absorb moisture from the environment. On the other hand, if you put a piece of wood with high moisture content into a dry (low humidity) environment, the wood will release moisture back into the environment.
This happens because wood is always trying to reach its Equilibrium Moisture Content or EMC. This is the point where wood is in balance with its environment and is no longer releasing or absorbing moisture. If a piece of wood is left in any environment for long enough, it will eventually reach its EMC.
Before woodworkers, furniture makers, and wood flooring installers begin to work, they need to make sure the wood they’re using has already reached its EMC. If they don’t do this, the wood might continue to shrink and swell after their project is complete, resulting in deformities.
Anyone who creates a product with wood needs to use an accurate, reliable meter for moisture measurement purposes.
What are the different types of moisture meters?
There are two main types of wood moisture meters: pin-type and pinless.
Pin-type wood moisture meters
A pin wood moisture meter has two sharp pin tips that penetrate the wood. When the meter is turned on, an electrical current passes between the pins and measures the resistance. The technology behind pin-type wood moisture meters is based on the fact that wood doesn’t conduct electricity, but water does. Therefore, drier wood will have more resistance to an electrical current.
Pin-type moisture meters take readings at the depth of the pins. Pins come in different lengths and can also be attached to an external hammer probe for the deepest readings.
A pin moisture meter is sensitive to temperature variations as well as the wood’s chemical makeup. With a pin meter, you usually get a temperature correction chart along with it and a species correction chart. Before you use the meter, you need to specify which type of wood you wish to measure.
Although the pin’s tips are small, pin-type moisture meters still poke holes in the wood. They are invasive and because of this aren’t usually used on things like fine wood furniture. They are more commonly used for measuring moisture in lumber and sometimes wood floors.
Another drawback of a pin moisture meter is the pins themselves. It takes some pressure to push them into the wood. In fact, some wood species are so hard that pushing the pins into the wood requires considerable effort. Therefore, pins tend to bend or break and then need to be replaced. This is inconvenient and costs money, especially if it happens regularly.
Finally, if the surface of the wood is wet, a pin-type wood moisture meter may produce inaccurate readings as it will only read the moisture on the surface. This will, of course, affect the reading.
Pinless wood moisture meters
Pinless wood moisture meters don’t damage the wood by poking holes in it to take a reading. Instead, pinless meters use an electromagnetic sensor and scan from the surface of the wood to take a measurement. This makes them especially useful for measuring the moisture content of fine hardwood floors and expensive wood furniture.
Pinless wood moisture meters allow you to quickly scan a larger area of the wood. In contrast, pin-type meters only measure the moisture between the two pins. Using a pin moisture meter, you would need to take multiple readings (and create quite a few holes) to measure the same area.
While pin-type meters are sensitive to a wood’s chemical makeup, pinless wood moisture meters are sensitive to variations in wood’s specific gravity (i.e., density). All higher-quality pinless wood moisture meters will have a setting that allows you to specify the correct specific gravity for the species of wood you’re measuring.
Pinless wood moisture meters can take a moisture measurement from the wood’s surface down to a depth of about 1.5”.
Many pinless meters require the surface of the wood to be perfectly dry to get an accurate measurement. However, some higher-end pinless meters are able to take accurate moisture readings when the wood has a bit of surface moisture.
All pinless moisture meters need to be calibrated if you want an accurate reading. You can quickly perform a calibration check on most meters. If a meter needs to be recalibrated, this is generally done by the manufacturer. Wagner’s Orion® pinless moisture meters allow the user to recalibrate the device back to factory settings.
Buyer’s guide to pin-type and pinless wood moisture meters
Before you buy any moisture meter — pinless or pin-type — you’ll need to do your homework. To help you with that, we’ve put together a fairly comprehensive list of questions to ask.
Is the meter built to last?
What does the casing look like? Is it cheaply made or is it durable? Remember, you’re looking for a wood moisture meter that’s going to hold up under heavy use.
If it’s a pin meter, are the pins susceptible to breaking, bending, or coming loose? Can you glean any information about the meter from customer reviews?
What’s the lowest and highest moisture content the meter can read?
Is the meter able to take measurements as high as 30% moisture content and as low as 5% moisture content? Some moisture meters can take readings at lower moisture content levels than others. It all depends on the quality and type of meter. Make sure the moisture meter you’re considering has the correct range for your particular needs.
Is the meter easy to use?
Is the meter’s design intuitive or does it look like the cockpit of a 747? How long will it take you to learn to use it?
Take a good look at the documentation that comes with it. Is it easy to understand? Is it online and searchable? Is there enough documentation?
Are the battery and pins (for pin meters) easy to install?
Is the temperature compensation automatic or will you need to use a table?
Can you easily see and record data even while working in tight spaces?
Are you able to make sure the meter is correctly calibrated? How is it calibrated? Can you calibrate it yourself or do you need to send it to the manufacturer?
What features does it have?
Some of the features you might want to look for include:
- Low battery indicator
- Ability to store and retrieve data (individual readings)
- Precision to the nearest 1% or better
- Ability to upload data from the meter to your computer
- Carrying case or a pouch
What kind of customer support comes with it?
Support is important, especially when you need it!
- Are the manual, documentation, and conversion charts available online or offline?
- How long is the warranty? The longer, the better.
- How quickly does customer support answer emails? Can you get help by calling a number? (Moisture meter reviews will be a good source of information about support.)
- Does the manufacturer have a service repair center? Where is it?
How does the meter feel when you hold it? Do you like the way it feels, the material, size, shape, etc.? You should, because you’re going to be using it a lot.
Is the meter easy to carry around? Can it attach to your belt or easily fit into a pocket?
What about the buttons? Are they high-quality and easy to punch?
Moisture meter displays include LED and LCD display as well as analog. Whichever you choose, make sure the display is easy to read.
Does the meter produce accurate readings?
How do we know a meter is accurate? Enter the oven-dry test.
Moisture meter accuracy is determined by comparing the results obtained via the oven-dry test to those obtained using the moisture meter itself. The oven-dry test is very accurate which is why it’s used to test the accuracy of wood moisture meters. Here’s how it works.
A piece of wood is weighed and then placed in a special drying oven. Its weight is checked periodically because as the wood dries, the water will evaporate and the wood will get lighter. Once its weight stops changing, that weight is compared to what it was before being placed in the oven. The difference is used to calculate the original moisture content of the wood.
If we want to know the accuracy of any wood moisture meter, we need to compare its moisture content measurements (obtained before the wood is placed into the oven) to the results obtained via the oven-dry test.
A quality moisture meter that consistently produces accurate moisture content readings in the desired range is indispensable for anyone who works with wood. Other key things to look for in a moisture meter include ease of use, durability, available features and accessories, and customer support.
To help you make a smart, informed buying decision, you may also want to check out this review and comparison of today’s top-rated wood moisture meters.