The term firewood BTU is used to describe how much energy a fuel (firewood) has. Most people burn firewood for one reason....heat. So, it only makes sense to burn a firewood that generates high BTUs.
BTU or British Thermal Unit is the amount of energy required to heat one pound of liquid water by one degree fahrenheit.
To get the most energy out of your firewood the wood should be seasoned. Seasoned firewood is described as having a 20% moisture content.
Seasoning firewood takes time. A good rule of thumb is to cut firewood this year so you can use it next year.
Keep up the rotation and you will always have good, dry, seasoned wood to burn.
Burning green wood decreases the BTUs generated by the fire.
As the green wood burns, the energy created from the fire is used to evaporate the moisture resulting is wasted heat.
Green wood also tends to smoke and smolder creating the possibility for creosote to form in the chimney. The creosote will stick to the sides of the chimney and can ignite causing a chimney fire.
A cord of firewood measures 128 cubic feet. Typically the firewood is cut into 16 inch lengths and is tightly stacked in three rows, 4 feet high and 8 feet long, totaling 128 cubic feet.
The following chart describes the BTUs generated from different species of popular firewood.
As you can see there's a lot of different firewood species to choose from. Not all of the options listed above will be available to you since some trees only grow in certain parts of the country.
However, this chart can be very helpful because it gives you an idea of how various firewood types compare to each other. Generally speaking, hardwoods are much more dense and will create more heat than a softwood.
In the end, when I cut my own firewood I normally don't get too caught up on the exact amount of BTUs a specific firewood type creates.
As long as it's a good quality piece of wood, a few BTUs here and there really won't make a huge difference.
However, if you're going to buy firewood from someone else why not get the best firewood available especially if it's all the same price?