Fireplace BTU Output Calculator
Estimate the heat output (BTU/hr) of your fireplace based on fuel type, burn rate, and combustion efficiency.
Formula
Gross Heat Input (BTU/hr) = Burn Rate × Heating Value of Fuel
Net BTU Output (BTU/hr) = Gross Heat Input × (Efficiency% ÷ 100)
Heating values used:
• Dry cord wood: 8,600 BTU/lb
• Natural gas: 1,020 BTU/cu ft
• Propane: 21,600 BTU/lb
• Wood pellets: 8,500 BTU/lb
• Bituminous coal: 12,500 BTU/lb
Unit conversions: 1 kW = 3,412.14 BTU/hr | 1 MBH = 1,000 BTU/hr
Assumptions & References
- Wood heating value assumes properly seasoned (dry) cord wood with ~20% moisture content (USDA Forest Service).
- Natural gas heating value of 1,020 BTU/cu ft is the standard lower heating value (U.S. EIA).
- Propane heating value of 21,600 BTU/lb based on NFPA 58 / U.S. DOE data.
- Wood pellet heating value of 8,500 BTU/lb per Pellet Fuels Institute (PFI) standards.
- Bituminous coal heating value of 12,500 BTU/lb per U.S. EIA average.
- Typical open wood fireplace efficiency: 10–30%; wood stove: 60–80%; gas fireplace: 70–90%; pellet stove: 75–90%.
- Net BTU output represents usable heat delivered to the room after combustion losses.
- This calculator does not account for flue losses, radiant vs. convective heat distribution, or altitude adjustments.