Boiler Firing Rate Calculator
Natural Gas (approx. 1,000 BTU/ft³)
Natural Gas (100,000 BTU/Therm)
No. 2 Fuel Oil (140,000 BTU/Gallon)
Propane (91,500 BTU/Gallon)
Propane (2,500 BTU/ft³)
Total Input Firing Rate: BTU/hr
Fuel Consumption: per hour
How to Calculate Boiler Firing Rate
The boiler firing rate is the total amount of fuel energy a boiler consumes to produce a specific amount of heat output. Because no boiler is 100% efficient, the energy input (firing rate) must always be higher than the heat output provided to the building or process.
The Formula
To determine the firing rate, use the following core formula:
Firing Rate (BTU/hr) = Boiler Output (BTU/hr) / (Efficiency / 100)
Once you have the Firing Rate in BTU/hr, you can determine the physical volume of fuel consumed:
Fuel Consumption = Firing Rate / Fuel Heating Value
Common Fuel Heating Values
- Natural Gas: Approximately 1,000 BTU per cubic foot or 100,000 BTU per Therm.
- No. 2 Heating Oil: Approximately 140,000 BTU per gallon.
- Propane: Approximately 91,500 BTU per gallon or 2,500 BTU per cubic foot.
Why This Calculation Matters
Understanding the firing rate is essential for HVAC professionals and building managers for several reasons:
- Nozzle Sizing: In oil burners, the firing rate determines the size of the spray nozzle required.
- Orifice Sizing: For gas boilers, it determines the gas manifold pressure and orifice sizing.
- Energy Auditing: By comparing the actual fuel usage (clocking the meter) against the calculated firing rate, technicians can diagnose efficiency drops or combustion issues.
- Equipment Sizing: Ensures the boiler is adequately sized to handle the peak heating load of the structure.
Practical Example
If you have a boiler designed to deliver 170,000 BTU/hr of heat to a home and it has an AFUE (efficiency) rating of 85%, the calculation would be:
- Input BTU = 170,000 / 0.85 = 200,000 BTU/hr.
- If using Natural Gas (1,000 BTU/ft³), the boiler would consume 200 cubic feet of gas per hour (CFH).