Formula & worked example
η=Quseful/(mfuel·HV); loss=Qinput−Quseful.
100 kg/h fuel at 42 MJ/kg supplies 1,166.7 kW; 950 kW useful output corresponds to about 81.4% direct efficiency.
Heating & HVAC engineering calculator · Updated Sep 17, 2026
Boiler Efficiency Calculator — Fuel Input, Useful Heat & Fuel Cost
Calculate direct boiler efficiency, heat loss, useful output and fuel required from fuel rate, heating value and delivered thermal output.
Inputs
Live result
Fuel heat input 1,166.6667 kW
Direct efficiency 81.428571%
Heat loss/unaccounted 216.66667 kW
Fuel cost rate 80 per hour
Energy balance is physically bounded
Assumptions & limits
- Heating value basis must be consistent (HHV or LHV).
- This direct method does not itemize stack, radiation, blowdown or unburned-fuel losses.
Frequently asked questions
What does this Boiler Efficiency Calculator calculate?
Calculate direct boiler efficiency, heat loss, useful output and fuel required from fuel rate, heating value and delivered thermal output.
What units are supported?
Inputs state their unit basis and results include practical SI and US customary equivalents where useful, so the calculation can be checked against field data and equipment schedules.
Can I use this for final equipment selection?
Use it for transparent first-pass sizing and engineering cross-checks. Final selections should use measured conditions, manufacturer performance data and applicable codes or design standards.