Burning the Right Firewood

Why dry wood matters for the chimney

Freshly cut wood holds a lot of water. When you burn it, part of the fire's energy goes into boiling that water off. EPA's Burn Wise program points out that wet wood makes more smoke, produces less heat and tends to smolder.

For the chimney, the important part is temperature. CSIA explains that unseasoned wood produces cooler smoke, and cooler smoke condenses more readily on the flue walls as creosote. Dry wood burns hotter and cleaner, so less of the smoke turns into deposits. See Creosote: stages, risk and removal.

How to tell if wood is dry

EPA lists a few signs of well-seasoned wood. They are useful for a quick check, but a meter is more reliable.

• Darker color, often with cracks or checks in the end grain.
• Lighter weight than a fresh piece of the same size.
• A hollow sound when two pieces are knocked together, rather than a dull thud.

Bark that peels off easily and no green or wet look under it are also good signs. Surface appearance can mislead, though. A log can look gray and dry on the outside and still be wet inside, especially after a rainy fall.

Using a moisture meter

A pin-type firewood moisture meter is inexpensive and takes the guesswork out. EPA's Burn Wise instructions boil down to three steps:

1. Split a pieceTake a typical piece from the pile and split it so you have a fresh face. The outside of a log dries first and reads drier than the inside.
2. Test the fresh facePush the meter's pins into the newly split surface. Follow the meter's directions for pin direction relative to the grain and any setting for wood type.
3. Read the resultEPA's target is 20 percent moisture or less. Above that, set it aside to keep drying.

Test several pieces from different parts of the stack, and test wood you buy before you burn it.

How long wood takes to season

EPA's Burn Wise materials give these rough timelines:

These are starting points. Thick rounds, unsplit logs, dense oak and wood stacked in shade or in tight piles can take much longer. Wood that was cut, split and stacked in the open in spring will usually be in better shape by winter than wood cut in fall. The meter is the final word.

Hardwood and softwood can both burn well when dry. Hardwoods are denser and usually burn longer per piece. Softwoods light quickly and are good for kindling. Moisture content matters more than species.

Storing and stacking firewood

• Split before stacking. Split wood dries much faster than whole rounds.
• Get it off the ground. Use rails, pallets or a rack so the bottom row does not wick up moisture.
• Cover the top only. EPA advises covering the top of the stack and leaving the sides open so air can move through. A tarp wrapped down the sides traps moisture.
• Single rows in the sun and wind dry faster than deep piles in shade.
• Keep the main stack outside. Bring in only what you will burn in the next day or two. Stacking large amounts against the house or indoors invites insects and moisture problems.

What you should never burn

EPA lists materials that should never go in a fireplace or stove because they release toxic chemicals, damage appliances, or both. Put simply:

• Household trash, plastics, foam, rubber.
• Cardboard, wrapping paper, magazines and other glossy or colored paper.
• Painted, stained, coated or pressure-treated wood.
• Plywood, particleboard and other glued or manufactured wood products.
• Driftwood, especially from saltwater.
• Wet, rotted, diseased or moldy wood.

Use only small amounts of plain newspaper or a natural fire starter to get a fire going, not as fuel.

Manufactured fire logs are a separate category. If you use them, check your fireplace or stove manual first and follow the package directions. Some appliances are not approved for them.

Buying firewood

Firewood sold as "seasoned" is not always dry enough. A few practical steps help:

• Ask when it was cut and split, and how it has been stored.
• Bring a moisture meter or test a few split pieces as soon as it is delivered, before it goes on your stack.
• Look at the pile. Mold, fungus, a sour smell or a heavy, wet feel are bad signs.
• Know what you are buying. A full cord is a stack 4 feet high, 4 feet deep and 8 feet long. "Face cord" and "truckload" vary.
• Buy early. Wood bought in spring or summer has time to finish drying in your own stack.

If wood tests wet, stack it properly and give it time rather than burning it now.

Stoves and inserts are pickier than open fireplaces

Modern wood stoves and inserts are designed to burn efficiently with controlled air. That design depends on dry fuel. Wet wood in a stove tends to smolder, blacken the glass and leave deposits in the liner, and EPA's Burn Wise materials list dirty stove glass among the signs of wet wood.

Stove and insert manuals usually say what fuel the appliance is approved for, how large the pieces should be and how to load the firebox. Some prohibit specific fuels such as manufactured logs or coal. Follow the manual for your model.

EPA also notes that newer stoves built to current EPA emission standards produce far less smoke than older models. If you burn a lot and have an older stove, the type of appliance matters as much as the wood. See wood stove installation and service.

Burning it well

EPA recommends starting with a small fire of dry kindling or a natural fire starter and adding larger split pieces gradually. A few habits help the chimney too:

• Open the damper fully before lighting.
• Give the fire enough air to burn brightly rather than smolder.
• Add a few pieces at a time instead of packing the firebox.
• If you regularly see or smell smoke in the room, EPA says that is a sign something is wrong with the appliance or how it is used. Stop and get it checked. See Why does smoke come into the room?

Even with perfect wood, deposits still form over a season. Annual inspection and sweeping as needed still apply. See chimney cleaning.

Questions homeowners ask

Sources

1. U.S. EPA Burn Wise: Best wood-burning practices
2. U.S. EPA Burn Wise: How to use a moisture meter (PDF)
3. U.S. EPA Burn Wise: Wet wood is a waste (PDF)
4. U.S. EPA Burn Wise: Health and safety awareness kit, sample article
5. CSIA: Chimney fires and creosote

This guide is general information. It can't diagnose a specific chimney; an inspection can.