Heat duty (Q) is the rate of heat transfer required to change the temperature of a process stream. It is calculated as Q = m × Cp × ΔT, where m is the mass flow rate, Cp is the specific heat capacity, and ΔT is the temperature difference between inlet and outlet.

What units can I use for mass flow rate?

This calculator accepts kg/s, kg/hr, lb/hr, and lb/s. All are converted internally to a consistent SI base before computing, so you can mix common metric and imperial inputs freely.

What is a typical Cp value for water?

Liquid water has a specific heat capacity of approximately 4.186 kJ/(kg·°C) or 1.0 BTU/(lb·°F). For steam, organic solvents, or gases, values vary significantly — consult a fluid properties table for accuracy.

Does this calculator handle phase change (latent heat)?

No. This tool computes sensible heat duty only (temperature change with no phase change). For condensers, reboilers, or evaporators where phase change occurs, you must add the latent heat component (Q = m × λ) separately.

What is the difference between heating and cooling duty?

If the outlet temperature is higher than the inlet, the stream is being heated (positive duty). If the outlet is lower, the stream is being cooled (negative duty). The tool reports the absolute magnitude and labels the direction automatically.

Heat Duty Calculator

Name: Heat Duty Calculator
Availability: InStock
Author: Nham Vu

Calculate heat duty (Q = m × Cp × ΔT) for any process stream — enter mass flow rate, specific heat capacity, and inlet/outlet temperatures.

Process Stream Inputs

Mass Flow Rate

Specific Heat Capacity (Cp)

Water ≈ 4.186 kJ/(kg·°C) · Air ≈ 1.005 kJ/(kg·°C)

Temperatures

Inlet (T₁)

Outlet (T₂)

Output Unit

Heat Duty (Q)

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Summary

Calculate heat duty (Q = m × Cp × ΔT) for any process stream — enter mass flow rate, specific heat capacity, and inlet/outlet temperatures.

How it works

Enter the mass flow rate of your process stream (kg/s, kg/hr, lb/hr, or lb/s).
Enter the specific heat capacity (Cp) of the fluid.
Enter the inlet and outlet temperatures.
Select your preferred output unit (kW, BTU/hr, or kcal/hr).
The calculator applies Q = m × Cp × ΔT and displays the heat duty instantly.

Use cases

Size shell-and-tube or plate heat exchangers for process plants.
Calculate the heating or cooling load for a reactor feed stream.
Verify vendor datasheets for heat exchanger duty ratings.
Estimate utility consumption (steam, cooling water) for a process unit.
Perform quick feasibility checks during process design.
Convert heat duty between kW, BTU/hr, and kcal/hr for different standards.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu