The short answer is yes. Moisture meters are indeed affected by temperature, some more than others.
Pin-type wood moisture meters are especially sensitive to variations in wood temperature and because of this, high-quality pin meters are sold with temperature correction charts.
Pinless wood moisture meters are also sensitive to wood temperature, but not nearly as much. In fact, it’s safe to say that pinless meters are really only affected by temperature extremes. We’ll go into more detail about this later on. But first, let’s talk about why accurate wood moisture meter readings are so important.
How Temperature Affects Wood and Why Accurate Wood Moisture Readings Are Important
Let’s start with a definition.
How is the moisture content of wood defined?
The moisture content of wood is defined as the ratio of the weight of water in a piece of wood compared to the weight of the same piece of wood without the water.
Moisture meters — both pin and pinless — determine the moisture content in wood. Measuring the moisture content in wood is important because wood is hygroscopic. In other words, it absorbs moisture from the environment and releases moisture back into the environment as the relative humidity fluctuates. This goes on until both the wood and the environment are in balance. At this point, the wood is no longer absorbing or releasing moisture. This is called the Equilibrium Moisture Content (EMC) of wood.
As wood absorbs moisture from the environment it expands. As it releases moisture back into the environment it shrinks.
In other words, wood’s physical size changes.
If you create projects with wood that hasn’t yet reached its EMC, they could deform later as the wood continues to either shrink or expand as it moves toward the EMC.
To give you an idea about how much wood shrinks or expands…
Although it does vary according to species, we can safely say that wood shrinks or expands about 1% across the grain for a 4% change in moisture content. (Wood expands or shrinks very little along the grain.)
This might not sound like a lot. However, it’s enough to cause significant problems with wood furniture, flooring, or any other wood project including issues with drawers, doors, joints, and even the project’s finish, which can warp or crack.
Nobody wants to spend hours on a wood project only to see it ruined because the wood wasn’t at the proper moisture content. This is why moisture measurement is so important.
You Can Avoid This Problem By Using a Quality Wood Moisture Meter
You can avoid these problems by using a quality moisture meter. A moisture meter will help you verify that the wood is at the correct moisture content before you start working on your project. It will also help you make sure the wood remains at the proper moisture content during construction because this is also important.
This applies to anyone who works with wood including hobbyists, professional flooring installers, cabinet makers, or anyone who sells wood building materials. They all need to know the moisture content of wood.
Now, depending on your geographic location, the correct wood moisture content for your project could be anywhere from 6 to 12%. A quality moisture meter will enable you to make sure the wood you’re working with is indeed at the proper moisture content for your location. And if you’re a woodworking professional, your reputation will depend on knowing this information.
How Temperature Affects Pin-type Moisture Meters
Pin-type meters work by measuring the resistance to an electrical current passing through the two pin tips, which have been inserted into the wood. The drier the wood, the more resistance there is to the current. This is because water plus impurities is a great conductor of electricity. When the amount of water in the wood decreases, the resistance increases.
So, what about temperature? How does it affect pin moisture meters?
An increase in wood temperature causes a decrease in resistance. This, of course, can affect the accuracy of a pin meter moisture reading. This is why quality pin meters come with temperature correction charts and instructions on how to use them.
Pin meters are also sensitive to wood’s chemical makeup. Because this varies according to the species of wood, quality pin meters will also ask you to input the type of wood before taking a meter reading.
How Temperature Affects Pinless Moisture Meters
Pinless moisture meters are far less affected by temperature than pin meters because they don’t rely on electrical resistance to find wood’s moisture content. As we mentioned above, high-quality pinless meter reading changes are affected only by wood temperature extremes. Therefore, you normally won’t get a temperature correction chart when you buy a pinless moisture meter.
Pinless meters are sensitive to wood density (also known as specific gravity) though. Because wood density varies according to species, you’ll want to make sure the specific gravity setting is correct before taking a meter reading.
Now, let’s go over some general differences between pinless and pin-type wood moisture meters…
Pinless vs Pin Wood Moisture Meters
How Pin Moisture Meters Work
Pin-type moisture meters have two small probes (or pins) that must physically penetrate the wood in order to take a reading. When the meter is turned on an electrical current passes between the pins and measures the resistance encountered. The depth of the readings depends on the size and length of the pins. There are also external probes available for even deeper readings.
Pin wood moisture meters work because while water with impurities and salts conducts electricity, wood doesn’t. Therefore, the drier the wood, the greater the resistance.
How Pinless Moisture Meters Work
Pinless meters don’t need to penetrate the wood to take a reading. Instead, an electromagnetic moisture sensor pad quickly scans deep into the wood from the surface of the wood. Pinless meters can measure moisture content from the surface down to .25” or for deep readings, down to .75” or even down to 1.5”.
Pinless meters are perfect for measuring the moisture content of expensive furniture and hardwood floors because they don’t poke holes in the wood.
Pins vs a Sensor Pad
Because pin-type meters only measure the resistance between the two pins, you might have to take several readings (and poke quite a few holes in the wood) to get an accurate picture of the wood’s moisture content. This might not be a problem if you’re measuring the moisture content of firewood. However, this could be a big problem if you’re trying to measure the moisture content of fine wood objects like floors and furniture.
Pinless meters, on the other hand, can quickly scan a large area of wood enabling you to get an accurate picture of wood moisture content in mere seconds.
Pins Bend and Break
One drawback of pin meters is bent or broken pins. This happens because it can take significant pressure to push the pins into denser species of wood. Sure, pins can be replaced, but if this happens a lot the cost can really add up. Anyone who uses a pin meter should keep replacement pins on hand, just in case.
Pinless meters, of course, don’t have this problem.
Both Pin and Pinless Meters Need to Be Calibrated
Both pin and pinless moisture meters need proper calibration in order to give accurate readings. When you buy either type of meter it should include information about calibration and recalibration.
To sum up…
There are pin-type and pinless meters with prices and features to fit the budgets and needs of both hobbyists and professionals. However, most pros who work with wood prefer pinless meters because…
- They don’t poke holes in wood.
- You don’t need to deal with broken or bent pins.
- You can quickly scan large pieces of wood.
- They usually don’t need to be corrected for temperature.
- They’re just super easy to use. All you need to do is turn on the device and start scanning the wood once the proper species has been entered into the meter.
For additional information on buying a moisture meter, click here.