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What Moisture Content Should Firewood Be?

The logs hiss and steam on the coal bed instead of catching. Dark smoke rolls, the glass blackens, and the stove that heated the room last year barely warms it now. The wood looks fine. It is probably not fine. The question underneath all of it, what moisture content should firewood be, has a single number as an answer: 20% or less.

What moisture content should firewood be? The 20% rule

Every serious source lands in the same place. The EPA's wood-burning guidance says 20% moisture or less is best. University extension testing puts properly seasoned firewood below 20%. Stove manufacturers print the same number in their manuals: ideal moisture and seasoned firewood should be less than 20%.

The scale helps the number make sense. Fresh-cut oak runs about 75% moisture. That is three-quarters water by the oven-dry measure, which is why a green log barely burns: most of the fire's energy goes into boiling water out of the wood instead of heating your house. At 25% and above, wood is still wet. It lights poorly, smokes heavily, and lays down creosote in the chimney, which is a genuine fire hazard, not just a dirty flue. At 20% or below, wood catches on a hot coal bed, burns with bright flames and minimal smoke, and gives you the heat you paid for. Kiln-dried premium wood can read as low as 8%, but for air-dried wood, anything under 20 is the goal.

One thing I want to be honest about: no single reading tells you the whole story. A meter measures the spot you probe, and a split that read 18% in the shed can pick up surface moisture after a week of rain. The reading is a snapshot, not a certificate. What it does tell you, reliably, is whether the wood was seasoned in the first place, and that is the question that matters at purchase time.

How to test it: the meter and the no-meter checks

A pin-type moisture meter is the definitive test and the cheapest one, with quality models running $20 to $60. Technique matters more than the brand. Split a piece open first, then push the two pins into the freshly exposed end grain, along the grain rather than across it. Test the inside face, not the bark side and not the weathered outer surface, which reads drier than the wood actually is. Pinless meters exist, but they only read the outer inch or so and are less accurate on irregular split logs.

Without a meter, stack the cues. Seasoned wood is darker and grayer than green wood, with weathered ends. Look for radial cracks running outward from the center of the cut face; checking is one of the more reliable visual signs. Pick it up: seasoned wood is noticeably lighter, because water is heavy. Knock two pieces together. Dry wood rings with a hollow knock, wet wood thuds. Bark that falls off in your hands is another good sign.

No single cue is proof, and the stove-manual advice is to use as many indicators as possible. End-grain checks can appear on wet wood and be absent on dry wood. But four cues pointing the same way is a reading you can trust, and it costs nothing.

The buying move: test before you pay, not after. Split one log from the delivery on the spot and meter the fresh face. If the seller will not let you split a test piece, that tells you what you need to know. Once you know your winter demand from the firewood calculator, buy and stack a full year ahead, two for oak, so the seasoning happens on your schedule instead of the seller's promise.

Frequently asked questions

What moisture content should firewood be?

20% or less, measured with a pin-type moisture meter on the freshly split face of the wood. Wood above 25% is still wet: it lights poorly, smokes heavily, and produces excess creosote.

How do you test firewood moisture with a meter?

Split a piece open and push the meter's two pins into the freshly exposed end grain, along the grain, not across it. Test the inside face, not the bark side or the weathered surface. Quality pin meters cost $20 to $60.

Can you tell if firewood is seasoned without a moisture meter?

You can get close. Seasoned wood is darker and grayer, has radial cracks in the end grain, feels surprisingly light, rings with a hollow knock when two pieces are struck together, and sheds its bark easily. A meter removes the guesswork.

Why does burning wet firewood matter?

Energy that should heat your house goes into boiling water out of the wood instead. Wet wood burns cooler and dirtier, produces heavy smoke, and deposits creosote in the chimney, which is a fire hazard.

Can firewood be too dry?

For practical purposes, no. Firewood reaches equilibrium with the air around it, so air-dried wood bottoms out around 12 to 15% in most climates. Drier is better; there is no danger in overseasoning.

Size your supply for the season

Once your wood tests dry, figure out how much of it you need with the firewood calculator. Read how long firewood takes to season by species and how to tell if firewood is seasoned for the full picture. For more firewood guides, subscribe to the newsletter, it is free.