It is quite possible that a smoky fireplace or wood stove problem can be solved by using the right wood, so:
Know your wood
Firewood from different species or types of trees varies widely in heat content, burning characteristics and overall quality. Table I below presents several important burning characteristics for most species.
Green weight is the weight of a cord of freshly cut wood before drying. Dry weight is the weight of a cord after air drying. Green firewood may contain 50 percent or more water by weight. Green wood produces less heat because heat must be used to boil off this water before combustion can occur. Green wood also produces more smoke and creosote than dry wood. Firewood always should be purchased dry or allowed to dry before burning.
Dry wood may cost more than green wood because it produces more heat and is easier to handle. A wood's dry weight per volume, or density, is important because denser or heavier wood contains more heat per volume. It is best to buy or gather dense woods such as oak, ash or mulberry.
Hardwoods, or woods from broadleaved trees, tend to be denser than softwoods, or woods from conifers. Some firewood dealers sell "mixed hardwood" firewood. This may or may not be desirable, depending on the proportion of low-density hardwoods, such as cottonwood, that are included.
Table I also contains information on other characteristics that determine firewood quality. Ease of splitting is important because larger pieces of wood usually must be split for good drying and burning.
Fragrance and tendency to smoke and spark are most important when wood is burned in a fireplace. Woods that spark or pop can throw embers out of an open fireplace and cause a fire danger. Conifers tend to do this more because of their high resin content.
Woods that form coals are good to use in wood stoves because they allow a fire to be carried overnight effectively.
TABLE I. Firewood Facts
The amount of heat per cord of dry wood is presented in Table I. Heat content is shown as a percent of dry green ash, a common Nebraska firewood. Values above 100 signify a higher heat content than green ash and values below 100 a lower heat content.
Nice chart found while visiting a University of Nebraska-Lincoln and the United States Department of Agriculture web site.
More Firewood Notes
Wood supply preparation
Wood should be dried as much as possible before burning. Properly seasoned
wood has about 7,700 BTU maximum usable energy per pound versus only about 5,000
BTU available from green wood. For best results, season or air-dry wood for at
least six to eight months after cutting. This should bring the moisture content
down to 15 to 20% by weight.
All firewood contains water. Freshly cut wood can be up to 45% water, while well seasoned firewood generally has a 20-25% moisture content. Well seasoned firewood is easier to start, produces more heat, and burns cleaner. The important thing to remember is that the water must be gone before the wood will burn. If your wood is cut 6 months to a year in advance and properly stored, the sun and wind will do the job for free. If you try to burn green wood, the heat produced by combustion must dry the wood before it will burn, using up a large percentage of the available energy in the process. This results in less heat delivered to your home, and literally gallons of acidic water in the form of creosote deposited in your chimney.
Wood is composed of bundles of microscopic tubes that were used to transport water from the roots of the tree to the leaves. These tubes will stay full of water for years even after a tree is dead. This is why it is so important to have your firewood cut to length for 6 months or more before you burn it, it gives this water a chance to evaporate since the tube ends are finally open and the water only has to migrate a foot or two to escape. Splitting the wood helps too by exposing more surface area to the sun and wind, but cutting the wood to shorter lengths is of primary importance.
There are a few things you can look for to see if the wood you intend to purchase is seasoned or not. Well seasoned firewood generally has darkened ends with cracks or splits visible, it is relatively lightweight, and makes a clear "clunk" when two pieces are beat together. Green wood on the other hand is very heavy, the ends look fresher, and it tends to make a dull "thud" when struck. These clues can fool you however, and by far the best way to be sure you have good wood when you need it is to buy your wood the spring before you intend to burn it and store it properly.
(Notes complied from: http://www.oda.state.or.us/Measurement_Standards/laws_and_regs/fuelwood_facts.html)