TryBuildCalcSensible Heat CFM Calculator (Q = 1.08 × CFM × ΔT)
Convert sensible load to CFM instantly.
🕒 Last updated: September 15, 2026
Inputs
ℹ️Sensible load only — do not use total cooling load, since latent moisture removal isn't part of this equation.
ℹ️Absolute difference: room minus supply air for cooling, or supply minus room for heating.
Calculated Design Airflow
1,200 CFM
Sensible Load to CFM
Sensible Load
25,920 BTU/hr
Temperature Difference
20°F
Airflow per 1,000 BTU/hr
46.3 CFM
Assumptions Used
Uses the standard-air sensible heat relationship Q = 1.08 × CFM × ΔT, where 1.08 combines standard air density (0.075 lb/ft³), specific heat (0.24 BTU/lb·°F), and minutes per hour. This assumes standard air density and does not self-correct for altitude. Enter sensible load only — the equation excludes latent (moisture-removal) cooling entirely, so using a total cooling load here overstates the required airflow. The displayed CFM is rounded up, never to nearest, so it never understates the calculated requirement.
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete HVAC Airflow / Room CFM Calculator.
Sensible heat to CFM sizing
CFM = Sensible Load (BTU/hr) ÷ (1.08 × ΔT) is the standard relationship between a sensible heat load and the airflow needed to carry it, where 1.08 is standard air's specific heat capacity per unit volume per hour.
This page defaults to a 25,920 BTU/hr sensible load at a 20°F design split — edit the inputs above to match your own load calculation.
HVAC Airflow Formulas
Each mode uses its own independent formula — pick the one that matches what you already know, not the one that seems simplest.
Sensible Load to CFM
CFM = Sensible Load (BTU/hr) ÷ (1.08 × ΔT °F)
ΔT = absolute supply-to-room temperature difference
The 1.08 factor is standard air's specific heat capacity per unit volume per hour (60 min/hr × 0.075 lb/ft³ standard air density × 0.24 BTU/lb·°F) — a textbook ACCA/ASHRAE relationship, not a rule of thumb. It assumes standard air density and does not self-correct for altitude or unusual conditions. Use sensible load only; the equation has no term for latent (moisture-removal) heat. The displayed CFM is rounded up, never to nearest, so it never understates the calculated requirement.
Equipment Capacity to CFM
Target CFM = Cooling Tons × Selected CFM/ton
Safe planning band = Tons × 350 to 450 CFM/ton
400 CFM/ton is ACCA's own cited baseline, balancing sensible and latent capacity at standard conditions (80°F/50% RH). The 350–450 CFM/ton band is bounded by real coil failure modes, not an arbitrary range: below it, the coil risks icing; above it, condensed moisture risks blowing off the coil before it drains. This is a preliminary planning target — the matched equipment's own blower performance table at its actual installed external static pressure governs the final airflow.
Room-by-Room Allocation
Cooling Factor = System Cooling CFM ÷ Total Cooling Sensible Load
Room Cooling CFM = Cooling Factor × Room Cooling Sensible Load
Heating Factor = System Heating CFM ÷ Total Heating Load
Room Heating CFM = Heating Factor × Room Heating Load
Room Design CFM = larger of Room Cooling CFM or Room Heating CFM
This is a proportional split of a known system airflow — not an independent calculation of what each room needs on its own. Room and total loads must come from the same load calculation, or the resulting percentages don't represent anything real. The larger of the two seasonal values becomes each room's branch target, since the same duct and register have to serve both seasons.
Worked Example
This example walks through your current inputs above, using the same steps as the Formula section.
Input Values Used
| Input | Value |
|---|---|
| Sensible load | 25,920 BTU/hr |
| Temperature difference | 20°F |
Step-by-Step Calculation
| Step | Calculation | Result |
|---|---|---|
| Denominator (1.08 × ΔT) | 1.08 × 20 | 21.6 |
| Design CFM (exact) | 25,920 ÷ 21.6 | 1,200 CFM |
| Design CFM (rounded up) | ceil(1,200) | 1,200 CFM |
Therefore, a 25,920 BTU/hr sensible load at a 20°F split needs 1,200 CFM.
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Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.