Airflow (CFM) Calculator from Sensible Load and ΔT
Determine required air flow rates.
Project & Input Data
Your project criterion: enter the value from your governing code, specification or approved supplier data. No standard value is assumed.
Your project criterion: enter the value from your governing code, specification or approved supplier data. No standard value is assumed.
A standard-air default, editable for different altitude/temperature conditions.
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.
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).
| Result | Value |
|---|---|
| ΔT | 10 °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.
Next step and related links
Related calculators
- Duct Velocity CheckHVAC Design
- ACH CalculatorHVAC Design
- Duct SizingHVAC Design
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