Can You Burn Wet Wood in a Fireplace?

Where the heat goes when the wood is wet

Before wood can burn, the fire has to drive the water out of it. With wet logs, a large share of the heat goes into making steam rather than warming the room. You hear it as hissing, and you see it as froth or bubbling at the cut ends. The flames stay low and orange, the fire keeps collapsing back to smoke, and the room gets more haze than heat.

That smoke is cooler and heavier than smoke from dry wood. Draft depends on hot gas rising, so a cool, wet fire pulls weakly. On a still or humid evening some of the smoke rolls out under the top edge of the fireplace opening instead of going up the chimney.

In a wood stove or insert the effect is sharper. Wet wood keeps the firebox too cool for the secondary burn, the glass blackens within minutes, and owners often respond by turning the air down to make a load last, which makes the smoke cooler still. Stove manuals specify dry wood for this reason.

Why the flue takes the damage

Smoke from a smoldering fire is loaded with unburned tars and gases. As it rises into the colder upper part of the flue, those condense on the walls as creosote. Sweeps describe it in stages. The first is a dry, flaky soot that brushes off easily. The second is crunchy, tar-like flakes. The third is a hard, shiny glaze, almost like a coat of black enamel, which is difficult to remove and burns intensely if it ever catches.

Wet wood pushes a chimney toward the later stages quickly. Old houses make it worse: an exterior chimney loses heat to the weather, a tall flue gives smoke more time to cool, and many older fireplaces have flues sized for coal fires that are larger than a modern wood fire can keep warm. Creosote also narrows the flue, so each fire draws a little worse than the last. A fireplace that worked well in November can be smoking into the room by February.

Telling the kinds of wet wood apart

Not all wet wood is the same problem, and the fix depends on which kind you have. The EPA's wood-burning guidance describes seasoned wood as darker and lighter in weight, giving a hollow ring when struck against another piece.

The smell and the smoke in the room

Wet wood smells sharper and more sour than a clean wood fire. People describe it as acrid, or like wet leaves smoldering in a gutter. If that smell hangs in the room, smoke is spilling past the fireplace opening. Make sure the damper is fully open, crack a window near the fireplace to give the fire more air, and let it burn down instead of feeding it more damp logs.

A sour, smoky smell that lingers for days afterward, especially in humid weather or when the heat kicks on, usually comes from creosote in the flue rather than from the room. That is a sign the chimney is due for cleaning.

Drying firewood that got caught in a storm

A nor'easter that soaks an uncovered woodpile does not ruin it. Seasoned wood takes on water at the surface and gives it back fairly fast once air can move around it. A few steps speed that up:

• Split the soaked logs so the dry inner faces are exposed
• Bring in only a day or two of wood at a time and stand the pieces apart
• Keep indoor wood well back from the fireplace opening, radiators and space heaters
• Restack the main pile on a rack or pallets so it is off wet ground
• Pull any tarp off the sides so wind can pass through the stack
• Set green wood aside for next season instead of forcing it now

Buying firewood that is actually dry

Firewood sold as seasoned is not always ready. A delivery split last spring and dumped in a driveway, or bundles that sat on a sidewalk rack through a week of rain, can arrive with plenty of water still in it. Before you stack a delivery, split one or two pieces and look at the fresh face: pale and damp to the touch means green, dull and dry means it has had time.

Weight and sound help too. A dry split feels light for its size, and two pieces knocked together ring rather than thud. Ask the seller when the wood was cut and split, not just whether it is seasoned. Kiln-dried bundles are dry when sold but take on water again if they sit uncovered, so store them like any other firewood. For a fireplace used a few nights a month, buying a smaller amount of dry wood often beats a large load that is still drying.

Storing wood so it stays dry

Federal guidance from the EPA calls for seasoning firewood for at least six months, outdoors and off the ground with only the top covered, because covering the sides traps moisture. It puts the target at a moisture content below 20 percent and suggests checking with a wood moisture meter, a small handheld tool that reads a freshly split face. Its tips page adds that split wood seasons faster than whole rounds and that bringing kindling inside the night before helps it light.

Small rowhouse yards and city lots make this harder, not impossible. A narrow rack against a fence with a lid on top holds a winter's worth for an occasional-use fireplace. Keep the stack a little away from the house wall so air circulates and the siding or brick does not stay damp behind it.

After a season of damp wood

If the fireplace has been fed wet wood all winter, assume the flue has more creosote than usual and book a sweep before lighting the next season's first fire. Book sooner if you have seen black flakes falling into the firebox, smoke spilling into the room, or dark, sticky streaks on the damper or the face of the fireplace.

NFPA 211, the national standard, puts chimneys on a once-a-year inspection schedule, with cleaning whenever the deposits warrant it. During the visit the sweep brushes out the flue, notes which stage of creosote was there, and checks the flue tiles, damper and smoke chamber for anything the deposits were hiding. Glazed creosote may need more than one visit or a chemical treatment to break it down before it will come off.