Best firewood moisture meter: what to buy and how to read it

The best firewood moisture meter is a plain pin meter, not a pinless one. The General Tools MMD4E is the simple all-rounder; a meter with replaceable pins suits anyone who checks a lot of knotty, bark-heavy oak, and one with a big backlit screen helps if you take readings in a dim shed at dusk. Any of the three answers the only question that matters at the woodpile: does a fresh split face read under about 20 percent?

I put off buying one for two winters, on the theory that I could judge dry wood by feel. I could judge very wet wood by feel. The loads in the middle, sold as seasoned and really a couple of months short, fooled me every time, and each of them meant weeks of black stove glass and a cold kitchen. This guide is about choosing the meter and trusting what it says. For the signs of dry wood without a meter and how long drying takes, see our piece on how to tell if firewood is seasoned.

Pin or pinless: which kind of meter reads firewood?

A pin meter has two short metal pins that you push into the wood. It measures how easily a small current passes between them, and since water conducts and dry wood barely does, wetter wood reads higher. The reading comes from wherever the pins sit, so in the middle of a fresh split face you're measuring the inside of the piece, which is the part you're about to burn.

A pinless meter presses a flat sensor pad against the surface and reads a shallow layer of wood beneath it. It leaves no holes, which is why flooring installers and furniture makers favor the type. On a rough split face or a curl of bark, the pad can't sit flat, and the layer it reads is the part that dried first.

Firewood doesn't mind holes. It's going to be ash.

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What should a firewood meter have?

Every meter on the shelf promises accuracy. The differences that matter at a woodpile are plainer than that:

• Pins that can take abuse. Oak, knots and the odd bit of grit wear pins down and bend them. Look for a cap that covers them in your pocket and, if you test a lot of wood, replacement pins you can swap in.
• A wood setting. Many meters have separate modes for wood and for building materials such as drywall or plaster. Use the wood mode on splits, always.
• Species groups, if you can get them. Some meters let you pick a species group or include a correction table in the manual. Nice to have, not essential (more on that below).
• A screen you can read where you stand. A backlight and large digits help in a woodshed on a November afternoon. A hold button lets you pull the meter out and read it in better light.
• Batteries and auto-off. Small meters run on small batteries, and auto-off saves them. Keep a spare in the drawer with the meter.

The true measure of moisture in wood is slow kitchen work: weigh a sample, dry it in an oven until the weight stops dropping, then weigh it again. Nobody here did that with these three. I picked them from what each maker publishes in its listing and manual, then read owner reviews for the complaints that repeat after a winter or two, especially about pins and screens. So the list reflects careful reading, not an oven and a scale.

The General Tools MMD4E is the plain all-rounder of the three: push the pins into a fresh split face and read a percentage. The RDINSCOS meter comes with spare pins in the box, which earns its place if you split a lot of knotty oak or hickory that dulls the tips. The TopTes TS-630 has a large backlit screen that changes color with the reading, the easiest of the three to read in poor light or with tired eyes.

What does the number on the screen mean?

The reading is moisture content: the weight of water in the wood as a percentage of the weight of the wood once all its water is gone. That's the convention foresters and sawmills use, and it explains a quirk. A lab can report very green wood at more than 100 percent, because the water can outweigh the dry wood. Your meter can't go that high, so fresh-cut splits often simply read off the top of its scale.

The line to remember is about 20 percent, the same mark the U.S. EPA's Burn Wise program uses in its firewood advice. Here's how I read the bands, always on a fresh split face:

A single number is a sample, not a verdict. Two meters can disagree a little, and the same meter reads differently from one split to the next. That's why the method matters as much as the meter.

How do you get a reading you can trust?

Our seasoned-wood piece walks through the basic steps. These are the details that decide whether the number on the screen is honest:

• Read a fresh split face. Split the piece and test the new face straight away. Ends and outer faces dry first and will flatter the stack.
• Read across the grain. Line the two pins up across the grain and push them in as far as the meter allows, in the middle of the face.
• Stay clear of knots, checks and bark. A crack or a knot between the pins throws the reading off.
• Bring splits to room temperature. Carry a few inside the evening before. Cold wood reads low, and frozen wood can't be read properly at all.
• Test several splits. Pull pieces from the top, the middle and the shady end, and from each species in the stack. Judge the stack by its wetter pieces, not its best one.
• Write it on the wood. I chalk the date and the highest reading on an end piece of each row. A month later, I know which rows are moving and which aren't.

Do species settings matter for firewood?

Different woods conduct electricity a little differently at the same moisture, so better meters offer species groups, or the manual includes a correction table. Near the 20 percent line, the correction can shift a reading by a few points, which matters most when a row is sitting right on the edge.

If your meter has groups, pick the closest one for the wood you're testing. If it has a single wood setting, check the manual for the species it assumes; treat a reading in the high teens on dense oak as probably fine and a reading of 21 as a reason to wait. A mixed load is where settings break down, since no single setting suits oak, cherry and poplar at once. My fix is low-tech: sort by species when I stack, with the oak in its own row, since it dries slowest anyway.

Which parts wear out, and how do you look after a meter?

• Pins. Pull them straight out instead of rocking the meter side to side, which is how pins bend. Cap them before the meter goes in a pocket.
• Batteries. Cold drains them, and some manuals warn that a weak battery can skew readings. Swap at the first low-battery warning.
• Storage. Keep the meter in a kitchen drawer, not the woodshed. Damp and freezing nights do it no favors.
• Calibration. Some meters include a check function or a reference cap. If yours does, run it at the start of each season. Either way, stick with one meter so each season's readings compare with the one before.

Once you know which rows are dry, measure them with our firewood cord calculator so you know how many dry cords you're carrying into winter, and our guide to how much firewood you need for winter helps you judge whether that's enough.

A canvas log carrier makes the trips easier: test splits every few weeks through the fall, then the daily armload all winter.

The carrier made the list on duller grounds than the meters: the fabric and handle details in its published listing, and what owners report about the stitching after a season of daily trips. None of our firewood has ridden in it for this guide. For thermometers, alarms and the rest of the stove corner, see our wood stove accessories guide.

Common mistakes

1. Reading the end or the outside of a split instead of a fresh face.
2. Testing wood straight off a frozen stack.
3. Leaving the meter on its building-material setting.
4. Testing the one nice piece from the top of the pile and calling the stack done.
5. Pushing the pins into a knot or across a crack.
6. Buying a pinless meter because it leaves no holes.

Questions

Is an inexpensive meter accurate enough for firewood?

For the decision you need to make, yes. You aren't grading lumber; you're asking whether a split is under or over about 20 percent. Readings right on the line deserve another week or two and a second test, whatever the meter cost.

Can I use a pinless meter on firewood?

You can try, but it's the wrong tool. It needs a flat, smooth surface, and it reads only a shallow layer near the face. On split wood that means poor contact and a reading from the part that dried first.

Why does the middle of a split read wetter than the outside?

Wood dries from the outside in, so the core holds its water longest. The middle reading is the honest one, because that's the wood the fire has to dry out before it can burn well.

What should kiln-dried firewood read?

Comfortably under 20 percent, if it has been kept dry since the kiln. If a bundle reads in the mid-20s, it has been rained on or wasn't dried as long as the label suggests. Split one piece and read the middle; the meter settles the question in a minute, and a stove full of dry oak on the first hard frost is the whole point of owning one.