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Airflow / CFM Calculator

Determine required air flow rates.

HVAC Design SuiteStep 4 of 9

Project & Input Data

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Your project criterion: enter the value from your governing code, specification or approved supplier data. No standard value is assumed.

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Your project criterion: enter the value from your governing code, specification or approved supplier data. No standard value is assumed.

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A standard-air default, editable for different altitude/temperature conditions.

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A standard-air default, editable if needed.

Engineering Assumptions

Direct calculation — Sensible heat equation

  • The supply/room temperature difference is a user-entered design criterion.
  • All percentages and inputs are user-defined; the calculation is purely arithmetic and assumes no particular code or specification.

Formula Summary

  • Q(m³/s) = load(kW) ÷ (ρ × cp × ΔT)
  • ΔT = room temp − supply temp

Results

Enter your data and press Calculate to see the results.

Engineering Insight

A smaller supply/room temperature difference requires a larger airflow for the same load, affecting duct and fan sizing.

Recommended Action

Confirm the chosen temperature difference matches the terminal unit type before finalising the flow rate.

Next step

This calculator is fully usable as it is. Professional adds saved projects, calculation history and PDF/Excel reports; Premium adds the integrated workflows and the BOQ generator.

Workflow: HVAC Design SuiteAll tools in this disciplineCompare levels and pricing

Airflow follows directly from the sensible heat equation once you fix the supply air temperature. Enter the sensible load in kW and the room and supply temperatures, and the calculator returns the airflow in SI and imperial units so you can size diffusers and check duct velocity next.

Method and assumptions

Sensible heat equation

  • Q(m³/s) = load(kW) ÷ (ρ × cp × ΔT)
  • ΔT = room temp − supply temp
  • The supply/room temperature difference is a user-entered design criterion.
  • All percentages and inputs are user-defined; the calculation is purely arithmetic and assumes no particular code or specification.

Worked example

A 12 kW sensible load supplied at 14 °C into a 24 °C space (ΔT = 10 K).

Worked example results
ResultValue
ΔT10 °C
Flow (L/s)994 L/s
Flow (m³/h)3,578.5 m³/h
Flow (CFM)2,106 CFM

These figures are produced by the same calculator engine used on this page.

Frequently asked questions

Is latent load included?
No. The sensible heat equation only handles sensible load; enter the sensible portion of your total load.
Which ΔT should I use?
ΔT is room temperature minus supply temperature, both entered by you as design criteria. The tool assumes no standard supply temperature.
Can I use it for ventilation air changes?
Use the ACH Calculator for air-change based ventilation; this one is load-driven airflow.

Related calculators

Next step

Free calculators are open to everyone. Project saving and PDF/Excel reports come with Professional, and integrated workflows with Premium.