Not all firewood burns the same. The species of wood you choose for your outdoor furnace can mean the difference between a roaring, efficient fire that lasts through the night and one that fizzles out faster than you expect, and knowing the BTU content of each species helps you make a smarter choice before you ever split a single log.
What Is BTU and Why Does It Matter for Firewood?
BTU stands for British Thermal Unit. It is the amount of heat energy needed to raise the temperature of one pound of water by one degree Fahrenheit. When it comes to firewood, Outdoor Boiler Unit Heater BTU tells you how much heat energy a given wood species can produce when burned. The higher the BTU rating per cord, the more heat output you get, which means fewer loads, lower fuel costs, and a warmer home or workshop.
This matters especially if you are running an outdoor wood furnace, where efficiency directly affects how much wood you are hauling, splitting, and storing season after season.
How Is Firewood Measured? Understanding a Cord of Wood
Before diving into species comparisons, it helps to understand the standard unit of measurement for firewood: the cord.
A full cord of wood is a stacked pile measuring 4 feet wide x 4 feet tall x 8 feet long — or 128 cubic feet of total space. However, because logs are irregular shapes, the actual solid wood in that pile is usually only 70 to 90 cubic feet, depending on how tightly the pieces are stacked and how uniform their shapes are.
Because of this air space variability, all BTU values and weight figures in the charts below are approximate. Use them for comparison and planning, not as absolute guarantees.
Key Insight: One pound of dense hardwood and one pound of light softwood contain roughly the same BTU energy per pound. The real difference between species comes down to density. A cord of dense hardwood packs far more solid wood and therefore far more total BTU into that 128 cubic feet than a cord of lighter softwood does. Read the full article HERE.
Amount of Heat Energy in a Firewood Cord
Firewood BTU of Western Hardwood Species
Top pick: Live Oak leads Western hardwoods at 36.6 million BTUs per cord. If you have access to it, it is one of the best firewood choices on the West Coast.
Firewood BTU of Western Softwood Species
Notable: Douglas Fir tops the Western softwood list at 26.5 million BTUs per cord — comparable to some hardwoods, which is why it is such a popular choice in the Pacific Northwest.
Firewood BTU of Eastern Hardwood Species
Note: Some variation between data points may occur due to differences in laboratory testing methods and how solid wood volume per cord is calculated.
Top pick: Osage Orange is the Eastern champion at 32.9 million BTUs per cord, beating out even Shagbark Hickory. It burns incredibly hot and clean.
Firewood BTU of Eastern Softwood Species
Note: Some variation between data points may occur due to differences in laboratory testing methods.
Hardwood vs. Softwood: Which Is Better for Your Outdoor Furnace?
Here is a quick side by side comparison to help you decide what to burn:
Real example: A cord of Shagbark Hickory (27.7 million BTUs) will heat your space noticeably longer than the same volume of Eastern White Pine (14.3 million BTUs) more than twice the energy output for roughly the same amount of stacking work.
Does Moisture Content Affect BTU Output?
Yes! significantly. This is one of the most important factors that most people overlook.
Green (freshly cut) wood contains a high percentage of water, sometimes 50% or more of its total weight. That moisture absorbs heat energy as the wood burns, reducing the effective BTU output you get and increasing smoke production. According to the U.S. Department of Energy, properly seasoned firewood with a moisture content of 20% or less burns significantly more efficiently and produces far less creosote buildup in chimneys and flue pipes.
Moisture content comparison:
Always season your wood before burning it in an outdoor wood furnace. Most hardwoods need at least 12 months; very dense species like Oak and Hickory benefit from 18 to 24 months.
Quick Reference: Best Firewood Choices by Region
Pacific Northwest and West Coast
Best options: Live Oak, Eucalyptus, Pacific Madrone, Douglas Fir, Oregon White Oak
Midwest and Eastern U.S.
Best options: Osage Orange, Shagbark Hickory, Black Locust, Sugar Maple, White Oak, Beech
Northern Regions (shorter seasoning window)
Best options: Tamarack, Black Locust, Yellow Birch, White Ash (season faster than dense oaks)
If softwood is your primary option, use Douglas Fir, Western Juniper, or Rocky Mountain Juniper, as they offer the best BTU output in their category.
Frequently Asked Questions
What type of firewood produces the most BTUs? Among species commonly available in the U.S., Osage Orange (Eastern) and Live Oak (Western) top the charts. Both produce well over 30 million BTUs per cord when properly seasoned.
Is softwood worth using in an outdoor wood furnace? Softwood is not ideal as a primary fuel for an outdoor furnace because it burns faster and produces less heat per cord. That said, Douglas Fir and Western Juniper are solid performers and perfectly acceptable if hardwood is not available in your area. Softwoods are also excellent for kindling to get fires started quickly.
Why do BTU values vary between different charts and sources? BTU data can differ across sources because of variations in how much actual solid wood is measured in a cord (air space varies), differences in moisture content at the time of testing, and different laboratory methods. Treat all BTU figures as useful guides rather than exact values.
How do I know if my firewood is properly seasoned? Look for these signs: the wood feels noticeably lighter than when it was freshly cut, the ends show cracks or splits radiating outward, the bark peels away easily, and it makes a hollow clunking sound when two pieces are knocked together. A moisture meter is the most reliable tool, and you want a reading of 20% or below before burning.
Does the size of the firewood pieces affect BTU output? The BTU potential per pound stays the same regardless of piece size. However, smaller pieces ignite faster and burn more quickly, while larger chunks burn longer and more steadily. For an outdoor wood furnace, a mix of sizes generally works best smaller pieces to establish the fire, larger ones to sustain it.
Can I mix hardwood and softwood in my outdoor furnace? Absolutely. Many people use softwood to start the fire and hardwood to maintain a long, steady burn. Just make sure everything is well seasoned regardless of species.
How much firewood do I need for a winter season? This varies widely depending on your climate, the size of the space you are heating, how well insulated your home is, and the efficiency of your outdoor furnace. As a general starting point, many households in colder climates go through 3 to 6 cords per heating season. Tracking your usage the first year gives you the best estimate for future seasons.
Conclusion
Choosing the right firewood is one of the simplest ways to get more heat out of every cord you burn. Whether you are working with Western hardwoods like Live Oak and Pacific Madrone, Eastern standouts like Osage Orange and Shagbark Hickory, or making the best of the softwoods available in your area, understanding BTU content helps you plan smarter, store better, and stay warmer all season long.
The golden rules are straightforward: denser wood means more BTUs per cord, properly seasoned wood burns far more efficiently than green wood, and species choice should factor in what grows locally and what you can realistically split and store.
If you have questions about choosing the right outdoor furnace for your heating needs or want guidance on how to match your firewood supply to your system's output, contact us, we are happy to help you find the setup that makes the most sense for your property, climate, and budget.
