When it comes to moisture meters for wood, accuracy is important. Very important. If you can’t get accurate moisture content readings from your meter, it’s essentially worthless.
In fact, a wood moisture meter should consistently give accurate moisture content readings. Quality moisture meters do. Cheaper models not so much. In fact, low-cost moisture meters often give consistently in accurate readings (learn what a good moisture meter costs).
Moisture meter accuracy can be affected by a variety of things including the temperature of the wood, the environment, and even the temperature of the meter itself. Surface moisture on the wood and, when it comes to pin meters, something called ‘’cable interference’’ can also play a role in wood moisture meter accuracy.
We’re going to talk about these issues in detail.
Accuracy Depends on the Type of Meter and the Materials Being Tested
Pin-type Moisture Meters
As we noted above, the temperature of wood can affect the accuracy of a moisture meter reading. This is more of a problem with pin meters though. In fact, lower-end pin meters can be very sensitive to changes in wood temperature. This is why good quality pin meters come with temperature correction charts which you’ll need to use if you want to get an accurate reading.
A pin-type moisture meter can also be affected by the chemical composition of wood which varies from tree to tree, and species to species. Pinless moisture meters are primarily affected by a wood’s density, also known as ‘’specific gravity’’ (we’ll talk more about this below).
When it comes to pin meters especially, moisture measurement accuracy can even be affected by the temperature of the meter itself. If you leave your meter on a hot car seat in the sun for several hours and then take it into a chilly air-conditioned environment, you shouldn’t expect it to immediately produce accurate readings.
You will need to wait for the meter to cool down first. Remember, the temperature correction charts that come with pin meters are about the temperature of the wood, not the meter. The key here is understanding your meter’s limitations and how they can affect its accuracy.
There are a couple of other issues with pin meters that can affect accuracy.
When a pin moisture meter has a hammer probe with an attached cable, the way the user handles the cable can affect the accuracy of the reading by up to 2%. This is because the cable is surrounded by an electromagnetic field.
Also, when you push pins into wood that has a high moisture content, the reading can start to drift, or change. It’s not stable, in other words. Some manufacturers tell users to record the reading right away, within the first few seconds of pushing in the pins. However, depending on where the meter is being used, this might be difficult to accomplish.
Pinless Moisture Meters
As we noted above, pinless meters have their own accuracy issues. They are sensitive to variations in wood density or “specific gravity.” Because wood density varies from species to species, it’s necessary to input the correct species setting (often simply the specific gravity) before taking a reading.
Finally, both pin and pinless moisture meters can be affected by surface moisture on the wood. Some brands of meters are specifically designed to be less affected by this, while others have given it no consideration at all and are extremely affected.
Now, let’s talk a bit about how wood moisture meters actually detect moisture.
How Pin Meters Detect Moisture
Pin-type wood moisture meters have two, small electrode pins that need to penetrate the surface of the wood in order to take a reading. After the pins have been pushed into the wood an electrical current flows between them measuring the resistance.
This works because while water (with an electrolyte) conducts electricity, wood fibers themselves generally don’t. Therefore, if you want to find out how much moisture is in a piece of wood you measure the resistance to an electrical current. The drier the wood, the more resistance.
Note: Pin moisture meters measure the moisture content between the pins only. In other words, unless the piece of wood you’re measuring is very small, you’ll need to take more measurements than if using a pinless moisture meter to determine the wood’s moisture content.
One downside of pin meters is that the pins tend to bend or break. This happens in part because some woods are very dense and pushing pins into them can be quite difficult. Even the softest woods, though, will cause this to happen over time. Pins can be replaced, sure. However, if this happens a lot, it’s not only inconvenient, it can be expensive as well.
How Pinless Meters Detect Moisture
Pinless meters detect moisture via an electromagnetic sensor that scans into the wood. Because pinless meters don’t poke holes in the wood they’re very useful for measuring the moisture levels of expensive furniture and fine hardwood floors. They’re also able to easily and quickly scan large areas of wood.
How to Measure Moisture Content Using a Pin Moisture Meter
Step 1: Turn the meter on and make any necessary settings for the type of wood you’re measuring.
Step 2: Push the pins all the way into the piece of wood you’re measuring.
Step 3: Record the reading shown on the meter’s display.
Step 4: Repeat this same process at various intervals until you cover the entire piece of wood.
How to Measure Moisture Content Using a Pinless Moisture Meter
Step 1: Turn the meter on and then choose the correct setting for the species of wood you’re measuring and any other necessary settings. For example, some wood moisture meters come with a setting that allows you to adjust the depth of the reading.
Step 2: Place the meter on the surface of the wood and take a reading. Move the meter to take another reading, etc.
Moisture Meter Accuracy and Calibration
For accurate readings, moisture meters must be properly calibrated. If they’re off by even a couple of percentage points it can significantly affect your project. Unfortunately, over time moisture meters can fall out of calibration. You need to know when that happens and what to do about it.
Checking Moisture Meters for Calibration
There are a variety of ways to check a moisture meter — pin or pinless — for calibration. We’ll go over a few of them here.
Pin-type Meters
With high-quality pin-type meters, you can check the calibration using a calibration check device; basically a precision resistance source. If your meter is out of calibration, it will most likely need to be sent back to the manufacturer to be recalibrated.
Pinless Meters
Measuring the Moisture Content
The calibration of higher quality pinless meters can be checked via a calibration verification block (also called a sensor block). Using a calibration verification block is easy. Just place the scanning plate on the block, turn on the meter, and compare the reading to the value specified in the instructions. If it’s different, then you may need to send your meter back for recalibration by the manufacturer.
Note: You need to use a calibration block that’s designed to be used with your particular meter. Check with the meter’s manufacturer for more information.
On-Demand Calibrators for Pinless Meters
The highest quality pin and pinless meters either come with a calibration-check device or at least have one as an optional purchase. However, for recalibration, you’ll need to send the meter back to the manufacturer. This not only costs you money but also includes the inconvenience of downtime.
However, there are meters out there on the market right now that allow you to recalibrate the meter without sending it back to the manufacturer. It’s as simple as pushing a button and placing the meter on the calibrator.
So, are Wood Moisture Meters Accurate?
In a word, yes. Wood moisture meters can produce accurate readings. However, you may still be wondering how accurate are wood moisture meters. Well, let’s just say this. The accuracy of any wood moisture meter — pin or pinless — essentially depends on two things: The quality of the meter and its proper use. Even the highest quality moisture meter can produce inaccurate readings if the user doesn’t know how to properly handle it.
For more information on the accuracy of various moisture meters we’ve tested, check out our moisture meter reviews.