Sensible Heat Airflow Calculator (Q = 1.21·V̇·ΔT)
Sensible kW an airflow carries — or the CFM needed to move a sensible load.
The most-used equation in air-side HVAC. The 1.21 is ρ×c_p of standard air (1.2 × 1.006). At altitude, derate by the density ratio.
Formula
Sensible Heat Airflow Calculator (Q = 1.21·V̇·ΔT) is a free sensible heat formula for HVAC designers, technicians and energy auditors — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About Sensible Heat Airflow Calculator (Q = 1.21·V̇·ΔT)
Sensible kW an airflow carries — or the CFM needed to move a sensible load. The calculation implements Q(W) = 1.21 × L/s × ΔT (US: BTU/h = 1.08 × CFM × ΔT°F) (ASHRAE Fundamentals — air-side equations). The most-used equation in air-side HVAC. The 1.21 is ρ×c_p of standard air (1.2 × 1.006). At altitude, derate by the density ratio.
How to use Sensible Heat Airflow Calculator (Q = 1.21·V̇·ΔT)
- 1Enter Airflow in L/s.
- 2Enter Air ΔT in °C.
- 3Read Sensible heat instantly — no submit button needed.
- 4Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Sensible Heat Airflow Calculator (Q = 1.21·V̇·ΔT)?
- ✓Implements the standard formula — Q(W) = 1.21 × L/s × ΔT (US: BTU/h = 1.08 × CFM × ΔT°F)
- ✓Reference cited on-page: ASHRAE Fundamentals — air-side equations
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Live worked example: the substitution recomputes from your numbers
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the Sensible Heat Airflow Calculator (Q = 1.21·V̇·ΔT) use?+
It computes Q(W) = 1.21 × L/s × ΔT (US: BTU/h = 1.08 × CFM × ΔT°F), per ASHRAE Fundamentals — air-side equations. The formula is displayed under the result along with a worked example substituted with your own inputs.
What should I keep in mind when using this calculator?+
The most-used equation in air-side HVAC. The 1.21 is ρ×c_p of standard air (1.2 × 1.006). At altitude, derate by the density ratio.
Is this based on ASHRAE methods?+
The calculations follow the standard ASHRAE/ISHRAE formulations cited under the result, simplified where industry practice does the same. For permit-grade design, confirm with the full code procedure.
Is the Sensible Heat Airflow Calculator (Q = 1.21·V̇·ΔT) free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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