Temperature and Wood Moisture Measurement

Wood moisture meters are necessary because the relative humidity (RH) around wood is always changing, and so is the wood’s moisture content (MC).

Wood absorbs moisture from its ambient environment when the RH rises, and when RH decreases wood releases moisture.

Temperature works differently. Air temperature has a much smaller direct effect on wood’s MC than RH does, but the temperature of the wood itself affects pin meter readings, so a pin meter reading is only as good as its correction for wood temperature.

Relative Humidity

Lumber producers use kiln control systems to lower the MC of freshly cut (green) lumber. Ideally, they dry it to the MC it will be at in use, its equilibrium moisture content (EMC) for that environment.

As any weather watcher knows, the RH of the air is always changing, and wood’s MC changes with it.

Wood usually does not shrink or swell in use except if its MC changes in some way. The MC of wood changes when the RH changes.

Unfortunately, if the wood was at the wrong MC when it was put into use, it will move toward its EMC and may shrink or swell quite a bit in the process.

When you consider changes in MC, think changes in RH.

Temperature

Temperature alone doesn’t cause any significant size changes in wood, although heat does make moisture changes happen faster. The bigger effect is that when air is heated, its RH drops unless moisture is added.

For example, if it’s 30°F outside with 100% RH (snowing), the EMC is about 28%.

If that outside air is brought into a home and heated, you’ll see these RH and EMC values (EMC values per the USDA Forest Service Wood Handbook):

• Heated to 40°F: about 68% RH and 13% EMC
• Heated to 50°F: about 47% RH and 9% EMC
• Heated to 60°F: about 34% RH and 7% EMC
• Heated to 70°F: about 24% RH and 5% EMC

In much of North America, heated homes and offices run at roughly 6% EMC in winter and 9% EMC in summer.

Heating doesn’t remove moisture from the air, but it lowers the air’s RH. Without added humidity, the wood’s EMC drops, and the wood dries.

To keep the wood’s EMC in balance during winter months, homeowners can add moisture to the air by installing a humidifier in the furnace, as an example.

So while EMC changes can line up with rising temperatures, most of the change comes from the drop in RH that heating causes. Ambient temperature on its own has only a minor direct effect compared with RH.

But what about the temperature of the wood itself?

Learn more about temperature’s impact on wood moisture content in our guide.

Free Download – 6 Reasons Your Wood Project Failed

Moisture Meter Readings

A pin-style wood moisture meter’s readings must be corrected when the wood is warmer or cooler than about 70°F, so the MC readings stay accurate as the wood temperature varies.

Wagner Meters makes pinless handheld wood moisture meters that don’t need adjustments for most wood temperatures. Even frozen wood with an MC below 15% can be measured with minimal temperature concerns. (Call Wagner Meters before measuring frozen wood that may have a higher MC.)

If you’re planning a construction or renovation project, also read about moisture content in wood studs.

Shop Orion Moisture Meters

Larry Loffer

Larry Loffer is a senior technician at Wagner Meters, where he has over 30 years of experience in wood moisture measurement. With a degree in Computer Systems, Larry is involved in both hardware and software development of wood moisture measurement solutions.

Last updated on October 21st, 2026