The Science of BTUs: How Firewood Creates Heat
- Michelle Persolja
- Nov 1
- 4 min read
Updated: Nov 9
Ever wonder why some firewood burns hotter or longer than others? The answer comes down to BTUs — a simple but important measure of how much heat your wood produces. Understanding BTUs can help you choose the right firewood for your needs, whether you’re heating your home, enjoying a cozy fire, or cooking outdoors.
What Is a BTU?
BTU stands for British Thermal Unit. One BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.
When we talk about BTUs in firewood, we’re really talking about how much heat a certain amount of wood can release when burned. The higher the BTU rating, the more heat energy that wood will produce.
Why BTUs Matter
Firewood with a high BTU rating burns hotter and longer — which is great for home heating or wood stoves that you want to keep going through the night.
Lower-BTU woods burn faster and cooler, which can be ideal for short fires, outdoor gatherings, or quick cooking fires.
The main factors that affect BTU output are:
Wood species (density) – Denser woods have more mass and therefore more stored energy per cord.
Moisture content – Water in the wood must evaporate before the wood can burn efficiently.
Fireplace or stove efficiency – Not all the heat makes it into your living space; some is lost through the chimney or air vents.
Moisture and Heat Output
Even the highest-BTU firewood won’t perform well if it’s damp. “Green” or freshly cut wood can have moisture levels above 30 %, which means much of its energy is wasted boiling off water instead of producing heat.
That’s why Seasoned and Kiln Dried firewood make such a difference.
Seasoned Firewood (air-dried): below 20 % moisture
Kiln Dried Firewood: below 10 % moisture
0% Moisture Reading Kiln Dried Firewood
To put that in perspective, research from Oregon State University Extension shows that bone-dry wood yields about 8,000–9,500 BTUs per pound, while wood at 20 % moisture yields closer to 6,500–7,500 BTUs per pound. That’s roughly a 20 % loss in usable heat just from moisture!
Seasoned Firewood: Heat Output by Species
(Values shown per full cord of seasoned wood; actual heat output varies by moisture, appliance, and stacking method.)
Wood Species | Approx. BTUs per Cord (Millions) | Burn Characteristics |
Hickory | 27–30 | Very dense; long, hot burn |
White Oak | 25–27 | Consistent, steady heat |
Red Oak | 24–25 | Reliable, even burn |
Maple | 24 | Clean and consistent |
Ash | 23–24 | Easy to split; steady heat |
Cherry | 20–22 | Pleasant aroma, moderate heat |
Birch | 19–20 | Quick to ignite; bright flame |
(Sources: Wood-Heating-Solutions.com, Oregon State University Extension, Iowa State University Extension)
Kiln Dried Firewood: Heat Output by Species
Kiln dried firewood isn’t just dry — it burns hotter and more efficiently than air-seasoned wood. By reducing moisture to below 10%, more of the wood’s energy goes straight into heat rather than evaporating water. Here’s a look at how common hardwoods perform when kiln dried:
Wood Species | Approx. Heat Output (Millions of BTUs per Cord) | Why It’s Great |
Hickory | 29–32 | Dense and long-burning — perfect for steady heat all night. |
White Oak | 27–29 | Reliable and consistent; burns hot without frequent refueling. |
Red Oak | 26–28 | Even heat output; ideal for fireplaces or wood stoves. |
Maple | 25–27 | Clean burn and consistent heat — easy to manage. |
Ash | 25–26 | Splits easily and burns well even if slightly less dry. |
Cherry | 22–24 | Moderate heat with a pleasant, woodsy aroma — great for cozy evenings. |
Birch | 21–22 | Lights quickly and burns bright — perfect for quick fires or ambiance. |
These figures are approximate and based on published BTU values for well‑dried hardwoods, with an adjustment to reflect the additional drying found in kiln‑dried firewood (<10% moisture). Actual output varies by species, appliance efficiency, stacking, and log size.
Why Kiln Dried Makes a Difference:
Hotter, more efficient fires: Less moisture means more of the wood’s energy goes into heat.
Easier ignition: Lights quickly, even in damp conditions.
Cleaner burn: Less smoke, less creosote buildup, and fewer ashes.
Consistent quality: Every log is cut uniformly and tested for moisture.
With kiln dried wood, you get maximum heat with less effort, which makes it worth the slightly higher cost. It’s perfect for indoor fireplaces, stoves, firepits, and even cooking over wood.
Choosing the Right Firewood for Your Needs
Home Heating: Dense hardwoods such as Oak, Hickory, or Maple — higher BTUs for long, steady heat.
Casual Fires: Cherry or Birch — easier to light, good for shorter, aromatic burns.
Cooking: Hickory and Oak — consistent heat and great flavor for meats.
Keep in mind: every wood species will perform best when it’s properly seasoned and stored to stay dry.
Why Kiln Dried Firewood Is Worth It
There’s a common misconception that Kiln Dried firewood burns too fast — but that’s not really true when you understand what’s happening.
Because kiln dried wood is heated in a controlled environment, its moisture content is reduced to below 10%. That means it ignites quickly and burns efficiently.
When wood is properly dried, more of its energy is converted into heat instead of steam. So while the flame might appear more active, what you’re actually getting is a hotter, cleaner, and more complete burn. You’ll use fewer logs to reach the same comfort level — and that efficiency offsets the slightly higher price per cord.
Other advantages of Kiln Dried firewood:
Instant, reliable ignition — no frustration, even in damp weather.
Virtually no smoke or creosote buildup, which keeps your chimney cleaner.
Pest-free and mold-free — the heat treatment kills insects, larvae, and spores.
Perfect for indoor fireplaces and cooking, thanks to consistent moisture and clean combustion.
At The Firewood Co., our Kiln Dried hardwoods are carefully heat-treated and dried to well below 10% moisture reading before leaving our shop. It’s the premium choice for anyone who wants dependable, high-BTU heat with less smoke and more comfort.
Stay warm,
Nick & Michelle Persolja
The Firewood Co.
37859 Stevens Blvd
Willoughby OH
Seasoned & Kiln Dried Firewood Always in Stock!
We serve Lake, Geauga, Cuyahoga, Lorain, Summit, Medina, Portage, Trumbull, Ashtabula and Mahoning Counties.
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