You may think it's a little late to start worrying about your winter's supply of firewood. But there's still time to "stack" up.

A number of people are selling firewood right now, both seasoned and just-cut. In fact, firewood prices seem a little lower than at this time last year.

If you need to buy, keep in mind that when firewood is first cut, it contains a good bit of water. One fresh-cut cord of oak may have enough water to fill five and a half 55-gallon drums.

In a wood-burning stove or fireplace, that wood has to dry out before it will burn. And boiling off all that water steals a lot of heat away from the house.

That means the critical word when buying firewood is "seasoned." In general, the term means the wood has dried to a level that will allow it to burn easily and give up a high proportion of its heat value.

Well-seasoned firewood will have dried to a point that less than 20 percent of its weight is water. When the wood is first cut, water makes up 40 percent to 50 percent of its weight.

At the same moisture content, all wood produces about the same amount of heat -- pound for pound. The difference is that some woods are heavier than others.

Oak and hickory logs weigh more than the same size sweet gum or pine logs. That means you have to carry in and burn more pine or sweet gum logs to get the same amount of heat.

Because it has more natural resins, pine actually yields slightly more heat per pound than hardwoods.

The sticky, gum-like resins in pine firewood have given some people the impression that it produces more residue buildup, called creosote, than hardwood. Research has found this is not true.

The buildup on fireplace or wood heater walls, chimneys and flue pipes seems more a result of burning wood at relatively low temperatures.

When wood is heated, some of its chemical makeup is first changed to a gas and later ignited if the fire is hot enough. If the fire's not hot enough, they become part of the smoke. And if they contact a surface cool enough, they'll condense back to a liquid or a solid there.

Over time, this layer of creosote becomes thick enough that a hot fire will ignite it in place, causing a chimney fire.

Filling a wood stove at night and closing the damper to reduce airflow can keep a fire burning all night with no more wood. But it also is likely to form creosote.

Burning poorly seasoned wood favors creosote buildup, too, because evaporating water cools the burning process.

Burning small amounts of wood at high temperatures is one solution to the problem, but doing that by hand makes for busy and sleepless nights. The best solution I know of is automatic-feed wood-pellet stoves.

How can you tell if firewood is dry enough to burn well? It's not easy to tell. But there are ways.

One is to split a fireplace log and look at the split surfaces. Recently cut wood will have a darker center with lighter, drier-looking wood near edges or ends. Wet wood will be easier to split than dry wood, too.

When firewood is very fresh, the bark will be tightly attached. Bark on very dry logs usually can be pulled off easily.

The real indication is weight. Because of the water in it, unseasoned wood is heavier. Use a bathroom scale to compare a fixed volume (such as a cardboard boxful) of dry firewood with wood of unknown moisture content. That will tell something about the degree of seasoning.