Energy Balance Calculator

Calculate sensible heat, latent heat, total heat duty, and power requirements for process heating and cooling operations.

About this calculator

This calculator adds up the two ways a process stream absorbs or releases heat: sensible heat, which changes a fluid's temperature without changing its phase, and latent heat, which changes its phase without changing its temperature. Sensible heat follows Q = m × Cp × ΔT — mass flow rate times specific heat times the temperature difference between outlet and inlet — and is the dominant term whenever no boiling, condensing, melting, or freezing happens in the process. Latent heat follows Q = m × ΔHphase, where the phase-change mass and its heat of vaporization, fusion, or sublimation determine how much energy that transition consumes or releases, independent of any temperature change at all.

Because both terms carry the same sign convention (positive when the outlet state carries more energy than the inlet), a heating duty and its accompanying vaporization both add positively, while a cooling duty naturally computes as negative — the Power Required output takes the absolute value of that total and converts kJ/hr to kW, so it reports magnitude only, not direction. Leave Heat of Phase Change and Phase Change Mass at zero for a pure temperature-change process like heating water without boiling it; only fill them in when the stream actually crosses a phase boundary, since a nonzero latent term for a stream that never changes phase will overstate the true energy requirement.

Inputs

Mass Flow Rate

kg/hr

Specific Heat (Cp)

kJ/(kg·°C)

Inlet Temperature

°F

Outlet Temperature

°F

Heat of Phase Change

kJ/kg

Phase Change Mass

kg/hr

Tab to move between fields

Results

Sensible Heat

114,950 kJ/hr

Total Heat Duty

114,950 kJ/hr

Latent Heat0 kJ/hr

Power Required31.93 kW

How to Use This Calculator

Enter the Mass Flow Rate in kg/hr of the process stream.
Enter the Specific Heat (Cp) in kJ/(kg·°C): water = 4.18, air ≈ 1.005, oils ≈ 1.8–2.1 kJ/(kg·°C).
Enter the Inlet and Outlet Temperatures in °C to define the sensible heat duty.
If a phase change occurs (condensation, vaporization), enter the Heat of Phase Change in kJ/kg and the Phase Change Mass in kg/hr — set to 0 if there is no phase change.
Read the Total Heat Duty in kJ/hr and Power Required in kW to size heaters, coolers, or heat exchangers.
Compare Sensible Heat and Latent Heat contributions to understand which dominates the design.

How the result changes with Outlet Temperature

Outlet Temperature	Sensible Heat	Total Heat Duty
40	31,350 kJ/hr	31,350 kJ/hr
60	73,150 kJ/hr	73,150 kJ/hr
120	198,550 kJ/hr	198,550 kJ/hr
200	365,750 kJ/hr	365,750 kJ/hr

What each input means

Mass Flow Rate: Mass flow rate of the process fluid in kg/hr.
Specific Heat (Cp): Specific heat capacity of the fluid. Water is approximately 4.18 kJ/(kg·°C).
Inlet Temperature: Temperature of the fluid entering the heat exchanger.
Outlet Temperature: Desired temperature of the fluid leaving the heat exchanger.
Heat of Phase Change: Latent heat for phase change (e.g., 2260 kJ/kg for water vaporization). Set to 0 if no phase change.
Phase Change Mass: Mass flow rate undergoing phase change. Set to 0 if no phase change occurs.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Mass Flow Rate = 500, Specific Heat (Cp) = 4.18, Inlet Temperature = 25, Outlet Temperature = 80 = 6 input(s) provided
Calculate Sensible Heat
Sensible Heat
114950 = 114950
Calculate Total Heat Duty
Total Heat Duty
114950 = 114950
Calculate Latent Heat
Latent Heat
0 = 0
Calculate Power Required
Power Required
31.931 = 31.931

Engine last updated August 30, 2026. Checked against 4 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

When should I fill in the phase-change inputs versus leaving them at zero?

Fill them in only when the actual process stream boils, condenses, melts, or freezes somewhere between the inlet and outlet — for example, water being vaporized into steam. If the fluid simply changes temperature without a phase transition, leave both Heat of Phase Change and Phase Change Mass at zero, since including a nonzero latent term for a stream that never actually changes phase will inflate the total heat duty with energy that isn't really required.

Why does Power Required not tell me whether I'm heating or cooling?

Power Required is computed from the absolute value of the total heat duty, so it reports only the magnitude of energy transfer needed, not its direction. Check the sign of Total Heat Duty itself, or simply compare Inlet and Outlet Temperature, to see whether the process is a heating duty (outlet warmer) or a cooling duty (outlet cooler).

How do I pick the right specific heat value for my fluid?

Specific heat varies significantly by material — water sits around 4.18 kJ/(kg·°C), air is roughly 1.005, and typical process oils run 1.8-2.1 — so using water's value for a different fluid will produce a meaningfully wrong sensible heat result. Look up the actual Cp for your process fluid at its operating temperature, since specific heat itself can shift somewhat with temperature for real fluids.

Why do sensible heat and latent heat matter separately, not just as one combined total?

Knowing which term dominates tells you what kind of equipment you actually need: a process that's mostly sensible heat calls for a straightforward heat exchanger sized for temperature change, while a process with significant latent heat — like a reboiler vaporizing a distillation feed — needs equipment designed to handle the much larger, temperature-independent energy demand of the phase transition itself.

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