Boiler & Furnace Calculators
Boiler Blowdown Calculator
Calculate the boiler blowdown percentage needed to keep dissolved solids in boiler water below the safe maximum, based on feedwater and boiler water TDS.
Boiler Blowdown Flash Steam Recovery Calculator
Calculate the percentage of boiler blowdown water that flashes to recoverable steam when released to a flash tank.
Boiler Circulation Ratio Calculator
Calculate boiler circulation ratio from water circulation rate and steam generation rate.
Boiler Combustion Calculator
Calculate the total combustion air a boiler burner needs, including excess air margin, from fuel flow and stoichiometric air ratio.
Boiler Economizer Heat Recovery Calculator
Calculate heat recovered by a boiler economizer from flue gas mass flow, specific heat, and temperature drop.
Boiler Feedwater Heating Duty Calculator
Calculate feedwater heating duty in kW from mass flow rate, specific heat, and temperature rise.
Boiler Fuel Requirement Calculator
Calculate the fuel flow rate needed to generate a target steam output at a given boiler efficiency and fuel heating value.
Boiler Makeup Water Calculator
Calculate required boiler makeup water rate from blowdown rate and other water losses.
Boiler Steam Generation Calculator
Calculate boiler steam generation rate in kg/hr from fuel input, boiler efficiency, and enthalpy gain.
Boiler Superheater Duty Calculator
Calculate the additional heat duty needed to superheat steam from mass flow rate, specific heat, and superheat temperature rise.
Boiler Water Treatment Chemical Dosage Calculator
Calculate boiler water treatment chemical dosage from target concentration and water volume.
Furnace Combustion Gas Residence Time Calculator
Calculate how long combustion gases spend inside a furnace chamber from furnace volume and gas flow rate.
Furnace Draft Loss Calculator
Calculate total furnace draft loss by summing furnace pass, economizer, and stack pressure losses.
Furnace Heat Load Calculator
Calculate the heat load a furnace must supply to raise a mass flow through a specified temperature rise.
Furnace Residence Time Calculator
Calculate how long combustion gases remain in a furnace chamber given furnace volume and gas flow rate.
Furnace Volume Calculator
Calculate furnace or combustion chamber volume from length, width, and height for sizing and residence time calculations.
Furnace Wall Conductive Heat Loss Calculator
Calculate steady-state conductive heat loss through a furnace refractory wall using Fourier's law.
Steam Boiler Efficiency Calculator
Calculate overall steam boiler efficiency from steam flow, enthalpy gain, fuel flow, and fuel heating value.
Steam Boiler Evaporation Ratio Calculator
Calculate boiler evaporation ratio (kg steam per kg fuel) as a standard boiler performance benchmark.
Steam Quality (Dryness Fraction) Calculator
Calculate steam dryness fraction (quality) from actual enthalpy, saturated liquid enthalpy, and latent heat of vaporization.
Turning Fuel Into Steam, Efficiently
A boiler or furnace's job is converting fuel energy into usable heat, but not all of that energy makes it into the steam or hot air — some is always lost up the stack. These eight calculators cover the combustion, sizing, and efficiency math behind boiler and furnace design.
Check your own numbers with the Steam Boiler Efficiency Calculator, size fuel demand with the Boiler Fuel Requirement Calculator, or find blowdown rate with the Boiler Blowdown Calculator.
Why Condensing Boilers Are Not a Drop-In Upgrade
Condensing boilers require return water temperatures low enough to trigger condensation in the heat exchanger — usually below about 130°F. Many existing heating systems, especially older radiator systems designed around higher water temperatures, are not set up to run that cool, which is why a condensing retrofit often means more than just swapping the boiler itself.
Frequently Asked Questions
Does higher steam pressure mean better efficiency?
Not directly — pressure relates to the temperature an application needs, while efficiency is separately governed by how completely fuel energy transfers into steam rather than escaping as stack heat.
How is furnace volume relevant to heat load?
A furnace sized too small for its target volume struggles to reach or maintain temperature, so the Furnace Volume Calculator and heat load figures are typically checked together, not separately.
Related: Burner Calculators for burner-specific sizing, or Advanced Combustion Calculators for the underlying chemistry.