As temperatures dip and thermostats rise, many homeowners head for the nearest woodpile to stock up on firewood for the winter heating season. But unless they know what to look for when buying this popular source of heating fuel, those homeowners could be left out in the cold.“All firewood is not created equal,” warned Doug McLaren, forestry specialist with the University of Kentucky College of Agriculture. “There is a difference in the woods you can obtain, so it’s important to know what you’re getting.”There are two major considerations when buying firewood – potential heat content and how well seasoned, or dry, the wood is, McLaren said. When considering potential heat content, remember that wood is made up of air and cellulose (wood fiber). The more air space that wood has, the less there is to burn. Therefore, McLaren recommends buying wood with the heaviest/densest per unit volume.“The short list of good firewood would be Osage orange, hickory, black locust, all the oaks, sugar maple and ash,” he said. “All of those are very good firewoods, first of all, because they produce a very good fire and, second, because they are easy to split.”Yellow-poplar and silver and red maple provide much less heat per unit volume but are good for starting fires in the fireplace. Species to avoid include the elms, sycamore and sweet gum. “Even if they give it to you free don’t bring it home. They don’t make good fires, and because the fibers are interlaced, they will not split,” McLaren said.Most of the tree species that make good firewood are found in Kentucky. Supplies of such firewood are usually readily available, he added. However, suppliers sometimes will identify their firewood simply as “hardwoods” and won’t specify the species. “You simply need to ask,” McLaren said.The second thing to look for when buying firewood is how much water is in the wood. Because wood comes from a living plant, it contains water. And the more water in the wood, the less heat generated when it burns.“Wood is 50 percent moisture,” McLaren said. “It needs six months to a year to dry out enough to burn efficiently.”It is important to ask a firewood vendor if the wood is seasoned, but it’s equally important to check the wood for signs that it is dry: splits in the ends of the wood and a gray appearance, he said.Firewood is sold in a variety of measures. The forestry industry’s standard measurement is a cord – a load of firewood that measures 4 feet wide by 4 feet high by 8 feet long – but that’s often too much for the occasional user, as most homeowners are. Many vendors will instead price their firewood by the truckload.“What they usually do is sell it to the top of the truck bed, so the price of the load is going to be based on the size of the truck bed,” McLaren said.McLaren advises people to “shop around” before buying firewood. “It’s better if they go out and do some comparative shopping, just like with anything else they buy.”