Firewood: Softwood or Hardwood?



Q: A friend told us we shouldn’t burn our dead catalpa tree in our fireplace. Should we? What’s the best firewood? — A.S., North Salem

A: There’s a saying among those who cut, haul, split and stack logs to heat their homes: “The best firewood is whatever’s closest.” Even so, some woods burn efficiently — hot and slow — and catalpa isn’t one of them. But that doesn’t mean you can’t burn it at all.

Hardwoods like oak, beech, birch, ash, and black walnut score high on the BTU scale, which means they throw out the most heat for their volume. They burn longer and form “coals” that ignite any logs you put on top. Softwoods like pine and fir catch easily and burn fast. The best fires are built with a combination of soft woods to get them going, and slow-burning, hardwoods to provide heat. Catalpa is a soft, not very dense wood that works well as a starter, or to reignite a dying fire, as long as it’s thoroughly dry.

No matter the species, it’s important that firewood is well seasoned. Logs needs to be split and left to dry for about year before you burn them. Unseasoned, “green” wood with a high moisture content won’t burn properly. Worse, the moisture leads to creosote buildup in your chimney, which can cause a chimney fire. There’s a misconception that the pitch in softwoods creates more creosote, but it’s actually the moisture in the pitch that does that. Once any wood is thoroughly dry, the pitch acts as a high-octane fuel. One downside of low-density softwoods is that they tend to spit. 

If you buy firewood, the surest way to know it’s sufficiently seasoned is to keep it for a year yourself. Otherwise, there are telltale signs. Really dry logs look gray. They are relatively light for their size, with cracks on the ends and loose bark. They don’t smell  “woody.” If you bang a seasoned log, it makes a ringing sound. If you want to take a more precise approach, for about $35 you can get a digital moisture meter, with prongs to read the wetness of wood — below 25 percent is best. Measure from the split side of the log, not the end, which could be considerably drier.

Stack split wood on pallets or planks to keep it from absorbing moisture in the ground. Choose a spot with good air circulation. A wood crib is ideal, and looks cute, too, but you can loosely cover the stack with a tarp.

Remember: cozy and romantic as dancing flames in a fireplace can be, there’s no charm in a chimney fire. Get your chimney swept and checked at least once a year, if you use your fireplace frequently.