Generally speaking, all wood produces about the same amount of heat per pound when burned, regardless of whether it is a hardwood or a softwood. The main difference between woods is density. Five pounds of oak may be just one piece, whereas five pounds of catalpa could be three or four similarly sized pieces. Denser wood generally burns hotter and longer, and produces longer-lasting coals. But in some areas of North America, especially in very cold northern Canada, soft woods are the only ones readily available.
What matters most for an effective burn is the wood's moisture content. Wood with less than 20 percent moisture works well as firewood. Wetter wood can certainly be used, but it takes longer to light, and usually produces a lot of smoke.
Ultimately, any wood is effective if it has the right moisture content, has been cut and split for optimal use in the particular wood stove in which it will be burned, and has been properly seasoned, which means it has been stacked, stored and air-dried for at least one year.
Catulpa as Firewood
Individual pieces of catalpa do not give off as much heat as similar-sized pieces of a hardwood like oak or maple. This makes it perfect for fall and spring wood burning, when you don't want want your stove to overheat your house.
Even in the deep of winter, though, catalpa can do a good job of supplying heat; you'll just need to use it in larger quantities than you would hardwoods.
Catalpa is easy to split, even with a small hand axe. Because of this, it is a great wood to use for kindling when you start a fire or when, after an evening burn, you need to get the hot coals flaming again. If you have some dry catalpa, you can use it together with slightly wet hardwood to keep the fire lit.
Although lit catalpa does not burn as long as many other woods, many of today's more energy-efficient wood stoves have sophisticated draw mechanisms that will extend its burn time much longer than was previously possible.