Which Wood Moisture Meter Is Better: Shallow or Deep Scan?
When you’re picking a moisture meter for woodworking, you’re already thinking about factors like accuracy, cost, invasiveness (whether you want holes in your wood), and so on. And when you’re choosing a pinless meter, you also have to consider the thickness of the wood you’ll be working with.
Some meters work better with thicker wood, others with thinner … Those meters have different names: shallow-scan meters, deep-scan meters, and dual-depth meters.
So, how do you know which pinless meter to pick?
This page will guide you in making an informed decision. We’ll talk about:
- Similarities and differences between shallow- and deep-scan meters
- When to use a shallow-scan meter
- When to use a deep-scan meter
- When to use a dual-depth meter
Let’s first get an idea of what each type of meter is like.
Similarities and differences between shallow- and deep-scan meters
Shallow- and deep-scan meters are typically the same type of meter, the only difference being the depth at which they measure.
Shallow-scan meters typically measure about ⅜ to ¼ inch deep in the wood. Deep-scan meters, however, can read up to ¾ to 1 inch deep. Dual-depth meters take both shallow and deep readings.
To be clear, we are referring to pinless wood moisture meters.
Pin-type meters don’t “scan” the wood the way a pinless sensor does—they use two prongs, or pins, inserted into the wood. Using an electrical current between the two pins, these meters take the resulting resistance to determine the amount of moisture in that section of the wood. Pin meters generally read up to 5/16 inch deep, but some come with extensions or other features that allow them to read much deeper than that.
Pinless meters, on the other hand, send electromagnetic waves from a sensor plate on the bottom of the meter. These waves scan the wood to determine the moisture content levels.
Both shallow-scan and deep-scan meters work the same way, but their depth is different. Let’s look at why the depth of the scan is so important.
Why depth of scan matters
The depth a moisture meter is capable of scanning is important because not all parts of the wood are equal.
If you’ve ever ladled up a bowl of freshly cooked soup for yourself and set it on the table to cool, you’ll remember that around the edges of the bowl, the soup gets cooler, reaching a temperature you won’t burn your tongue at. But in the center of the bowl, the soup remains much hotter.
Something similar happens with moisture in the wood.
The surface of the wood tends to dry out faster and have less moisture—just as the soup around the edges of the bowl will cool faster. The core of the wood takes longer to dry out, and the soup in the middle of the bowl takes longer to cool down.
Some pieces of wood are thicker than others, so a deep-scan meter will allow you to reach the core and get a more accurate picture of the wood’s overall moisture content. A shallow scan meter, though, will be better suited for thinner wood.
So let’s look at the best applications for the different meters.
When to use a shallow-scan meter
Shallow-depth pinless wood moisture meters are best suited for thin materials, preferably ½ inch and under, since they usually penetrate to about a ¼ inch in depth.
So consider using a shallow-scan meter if you work with materials like:
If your meter can also scan other materials on a relative scale, it could work well for drywall. Using relative mode, you’ll be able to identify wetter and drier areas of the material.
When to use a deep-scan meter
A pinless sensor on a deep-scan meter often measures depths up to ¾ or 1 inch, making it suitable for thicker wood.
This would include building materials, such as nominal-length lumber (2x4s, 2x6s, etc.).
Woodworking projects that require a deep-depth pinless wood moisture meter are:
- Tables
- Some chairs
- Butcher blocks
- Etc.
These all need wood of a reasonably thick size.
But what if the piece of wood you want to measure is 2 inches thick? Or 3 inches? The deep-scan meter won’t be able to penetrate through the whole piece of wood.
In this case, you would measure the wood from both sides. Even if the deep scan still doesn’t reach all the way through—in other words, it can’t measure every millimeter of depth—measuring both sides will give you a more accurate reading than measuring only one side.
As with any piece of wood, you also want to take multiple readings in a stack of wood. If you only measure in one place, you could get a false high moisture reading or a false low one. Measuring across the stack will give you a broader picture of what the moisture is doing.
Another good practice when taking readings is to watch what is under your board. Leave an inch of air between the board and whatever is under it (like metal or concrete). Otherwise, the material underneath may throw the reading off.
When to use a dual-depth meter
Some meters combine the capabilities of both the shallow-scan and deep-scan meters to make what’s called a dual-depth meter. This meter has settings for both depths.
It’s a two-for-one deal that works great for woodworkers who use wood with a variety of thicknesses and don’t want to switch meters all the time (or risk getting those two meters mixed up!)
These meters would work great if you make furniture or other decorative wood pieces. A picture frame, for example, may use thin pieces of wood, requiring a shallow measurement. But the legs on a chair are pretty thick, and you’d need a deep scan.
The controls on a dual-depth meter allow you to change which mode you’re in depending on the project you’re working on. Some of these meters will allow you to store or hold readings too, so you don’t have to worry about writing down or remembering the information you need.
Which meter is best for you?
As we’ve described here, some meters work best for thin boards. Others work best with thick boards. And others can do the work of both.
Evaluate your own situation and needs before purchasing a meter. And as you research the best meter for you, be sure to check out our affordable, high-quality wood moisture meters—with all three depth options.