TryBuildCalcWhole-House CFM Calculator (Larger System, Sensible-Emphasis Airflow)
Estimate your whole-house airflow instantly.
🕒 Last updated: September 15, 2026
Inputs
ℹ️The selected equipment's nominal cooling capacity. This is a planning cross-check, not a substitute for the blower table.
ℹ️Lower airflow favors dehumidification; higher airflow favors sensible cooling. Manufacturer data governs.
Calculated Design Airflow
2,250 CFM
Equipment Tons to CFM
Equipment Capacity
5 tons
Selected Target
450 CFM/ton
350–450 Safe Band
1,750–2,250 CFM
Assumptions Used
Uses a selected CFM-per-ton planning target, not a substitute for the matched equipment's own blower performance table. 400 CFM/ton is ACCA's cited baseline balancing sensible and latent capacity at standard conditions (80°F/50% RH); the 350–450 CFM/ton band is bounded by real failure modes on standard coils — below it, coil icing; above it, moisture blow-off before drainage. 500 CFM/ton sits outside that band and needs the specific matched equipment's own manufacturer data before use.
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete HVAC Airflow / Room CFM Calculator.
Whole-house airflow sizing
A larger whole-house system (often 4-5+ tons) in a dry climate can favor the higher end of the safe CFM/ton band, since dehumidification matters less and additional sensible capacity is more valuable.
This page defaults to a 5-ton system at 450 CFM/ton — edit the inputs above to match your actual equipment and climate.
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 |
|---|---|
| Equipment capacity | 5 tons |
| Target airflow per ton | 450 CFM/ton |
Step-by-Step Calculation
| Step | Calculation | Result |
|---|---|---|
| Design CFM | 5 × 450 | 2,250 CFM |
| Minimum safe CFM (350/ton) | 5 × 350 | 1,750 CFM |
| Maximum safe CFM (450/ton) | 5 × 450 | 2,250 CFM |
Therefore, a 5-ton system at 450 CFM/ton needs 2,250 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.