Sensible Heat & Airflow Calculator
Work with the core air-side equation Q = 1.08 × CFM × ΔT: enter two values to get the third, with metric conversions and typical target airflows.
Last updated: 2026-09-15
How the calculation works
- The 1.08 factor bundles air density (0.075 lb/ft³) and specific heat (0.24 BTU/lb·°F) with the 60 min/h conversion.
- Leave one field blank to solve for it: airflow needed, heat delivered, or the resulting ΔT.
- The tonnage equivalent connects the answer to equipment sizing.
Formula
Q = 1.08 × CFM × ΔT Metric: Q(kW) = 1.2 × m³/s × ΔT(°C)
| Symbol | Meaning | Unit |
|---|---|---|
Q | Sensible heat transfer | BTU/h |
CFM | Airflow | ft³/min |
ΔT | Air temperature change | °F |
Worked example
Interpreting the result
This equation is the air-side heartbeat of HVAC: given equipment capacity and airflow it fixes the supply-to-return temperature split. Low airflow (clogged filter, weak blower) shows up as high ΔT, frozen coils in cooling, and heat exchanger stress in heating. Designers use 350–450 CFM per ton for cooling.
Assumptions
- Standard air at sea level — high altitude needs a corrected factor (1.08 × density ratio).
- Sensible heat only; latent (moisture) heat needs a separate wet-coil calculation.
Limitations
- Wet-coil (cooling with dehumidification) conditions need the total heat formula including latent load.
- High-altitude installations must correct for air density.
Frequently asked questions
What CFM per ton should I have?
350 CFM/ton in humid climates (better dehumidification), 400 in moderate, up to 450 in dry climates. Outside that range, check airflow and charge.
Why is my ΔT too high?
Usually low airflow — dirty filter, failing blower, or blocked returns. In heating, an over-fired furnace shows the same symptom.