Rückluftkanal-Rechner — Formel
## Return Air Sizing
**Grille Area = CFM / (Velocity x Free Area %)**
Return grilles must be large enough to avoid creating excessive negative pressure. The free area percentage accounts for the grille bars or louvers that block part of the opening. Keep return grille velocity below 400 ft/min for quiet operation.
**Grille Area = CFM / (Velocity x Free Area %)**
Return grilles must be large enough to avoid creating excessive negative pressure. The free area percentage accounts for the grille bars or louvers that block part of the opening. Keep return grille velocity below 400 ft/min for quiet operation.
Lösungsbeispiel
1,000 CFM system, 400 ft/min max grille velocity, 75% free area.
- Effective velocity = 400 x 0.75 = 300 ft/min
- Grille area = 1000 / 300 = 3.33 sq ft = 480 sq in
- Could use two 16x16 in grilles (512 sq in total)
- Return duct = 2 x sqrt(1000/400/pi) x 12 = 21.4 in