Return Grille Sizing Calculator
Free area and nominal size a return-air grille needs to stay quiet.
Undersized returns are the classic cause of whistling doors and starved blowers — most systems need MORE return area than supply.
Formula
Return Grille Sizing Calculator is a free return grille size 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 Return Grille Sizing Calculator
Free area and nominal size a return-air grille needs to stay quiet. The calculation implements A = Q/(V × free-area) (ACCA Manual D; grille manufacturer data). Undersized returns are the classic cause of whistling doors and starved blowers — most systems need MORE return area than supply.
How to use Return Grille Sizing Calculator
- 1Enter Return airflow in L/s.
- 2Enter Target face velocity in m/s (Returns: ≤ 2 m/s (400 fpm) for quiet).
- 3Enter Grille free-area ratio in %.
- 4Read Required core area, Square grille side instantly — no submit button needed.
- 5Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Return Grille Sizing Calculator?
- ✓Implements the standard formula — A = Q/(V × free-area)
- ✓Reference cited on-page: ACCA Manual D; grille manufacturer data
- ✓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 Return Grille Sizing Calculator use?+
It computes A = Q/(V × free-area), per ACCA Manual D; grille manufacturer data. 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?+
Undersized returns are the classic cause of whistling doors and starved blowers — most systems need MORE return area than supply.
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 Return Grille Sizing Calculator 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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