Choosing firewood that burns clean and dry

Moisture decides how a fire burns

Freshly cut wood holds a large share of its weight in water, and a fire has to boil that water off before the wood itself burns well. While it does, the fire runs cooler, smokes more and gives less heat to the room. The heat spent boiling water is heat the room does not get. The smoke from a cool, wet fire is heavy with water vapor and unburned gases, and when it cools in the flue, part of it condenses on the walls as creosote.

So the best wood to burn in a fireplace is chosen by dryness before the name of the tree. A dry piece of an ordinary species makes a cleaner, hotter fire than a wet piece of a prized hardwood. EPA Burn Wise sets the working target: wood burns best when its moisture content is below 20 as read on a wood moisture meter, after at least six months of seasoning.

How to tell dry wood from wet

Burn Wise describes seasoned wood as darker, lighter in weight, and hollow-sounding when two pieces are knocked together. Other signs follow from the same drying. Cracks open across the cut ends as the wood shrinks, bark loosens and peels, and a split face looks dull rather than bright and damp.

A moisture meter settles the question. Split a piece and press the meter's pins into the fresh split face, not the weathered outside, since a piece can be dry on the outside and wet in the middle. Take readings on a few pieces from different parts of the pile. Wood that hisses, steams or bubbles at the ends when it goes on the fire is telling you the same thing after the fact.

Hardwood, softwood and the pine question

Hardwoods such as oak and hickory are dense, so a dry split holds more fuel for its size. They take longer to catch, burn longer and leave a bed of coals. Softwoods such as pine are lighter. They catch fast and burn hot and quick, which makes them good for starting a fire and for short fires, though you will add wood more often.

The belief that pine fills a chimney with creosote blames the tree for what the fire does. Creosote comes from smoke cooling in the flue, and wet wood and smoldering fires are what feed it, whatever the species. Seasoned pine burned in a hot fire is fine in a fireplace. Resinous wood can pop and throw sparks more than dense hardwood, so keep the screen closed, and do not burn green pine that is still heavy with sap.

Seasoning and storing wood

Wood dries through its cut ends and split faces, so split it before it is stacked. Stack it in rows off the ground, on rails, pallets or a rack, with space between rows for air to move. Burn Wise advises storing wood outdoors with only the top covered, since covering the sides traps moisture in the pile. A shed with open sides works, and so does a tarp over the top only; a tarp wrapped down the sides does not.

Put the pile where it gets sun and wind, and keep it away from the walls of the house so moisture and insects stay off the siding. Bring indoors only what you will burn soon, and keep it at least 3 feet from the fireplace, which is the clearance fire safety agencies give for anything that can burn. Mark the stack with the date it was split, so you know which wood is ready first.

Buying firewood

Check seasoned firewood from a seller before you pay for it or stack it. Ask when it was cut and split, and take a meter to a few pieces if you can. A cord is a stacked volume of 128 cubic feet, such as a stack 4 feet high, 4 feet deep and 8 feet long, while terms like face cord or rick vary from seller to seller, so ask what the seller means in measured feet.

If a delivery arrives wet, it is not lost. Stack it the way described above and give it the time Burn Wise recommends before burning it. Kiln-dried wood is dried in a heated chamber and can arrive ready to burn, but the meter is still the test.

What not to burn in a fireplace

Burn Wise names most of what belongs on this list, and the manual for an insert or factory-built unit can add its own.

• Household trash of any kind, including plastics, foam and food packaging
• Cardboard, wrapping paper, and magazines or boxes with colored ink
• Painted, stained, coated or pressure-treated wood, including old decking and fence boards
• Wet, green or rotted wood
• Gasoline, kerosene, lighter fluid or charcoal starter to get a fire going
• Anything the maker of a fireplace insert or factory-built unit rules out in its manual

Burning it well

Start with newspaper, dry kindling or an all-natural fire starter, as Burn Wise suggests, and build up from small pieces to larger ones. Aim for a hot, lively fire, not a smoldering one, and add a split or two at a time instead of packing the firebox. A fire starved of air to make it last longer is the kind that builds deposits fastest. Once the fire is down to coals, let it burn out; a fresh load late in the evening only smothers it.

Manufactured fire logs are made for open fireplaces and come with their maker's directions, so follow the wrapper, including how many to burn at once and whether they can go in with firewood. They do not belong in a closed insert or stove unless its maker allows it.

What good wood does for the chimney

Dry wood burned hot leaves lighter, drier deposits in the flue, and those come off with brushes during a sweep. Wet wood and smoldering fires leave tar-like and glazed creosote that needs more work to remove and is more dangerous to leave in place. Good wood does not replace the yearly NFPA 211 inspection, but it changes what that visit turns up.

If you notice more smoke than usual, a darker, sticky deposit at the damper, or a fire that is hard to keep going, look at the wood first and then at the chimney. Our guide to the signs your chimney needs cleaning covers what to look for between visits.