Outdoor Unit Grille Sizing
Air-cooled condenser · niche / enclosed installation
How this works:The outdoor unit fan moves a fixed airflow (Q) through its condenser coil. When installed against a grille, this same airflow must also be drawn through the remaining grille area. The discharge zone is set by the unit faceprint, while the intake zone is sized by your target velocity and the grille's free-area coefficient (η).
Areas in:Velocity:
⚡
Condenser CapacityPRIMARY INPUT
Nominal cooling capacity at rated conditions (≈35 °C outdoor). From the nameplate or selection software.
Cooling capacity
9.50 TR33.4 kW114000 BTU/hr
💨
Condenser Airflow (Q)
Volume flow rate through the coil. Estimated from capacity, or taken directly from the catalog.
Calculation method
9500 CFM16141 m³/h4.483 m³/s
📐
Discharge Face Area
Frontal area of the unit pressed against the grille. Enter the unit size, type the area directly, or estimate it from the cooling load.
Input method
→ Estimated discharge area = 1.760 m² (18.94 ft²)
Area = 9.280e-4 × (114000 BTU/hr)^0.6482
Statistical estimate from 36 real outdoor units (R²≈0.85) — verify against the datasheet for final design.
🔲
Intake Grille Parameters
The remaining grille area drawing fresh air into the niche. Only part of a louvred/perforated panel is actually open.
Free area coefficient η
Louvres 30°
Design intake velocity
≡ 553 fpm
💡 Discharge face velocity = 2.55 m/s. Matching intake velocity to it balances resistance between both grille zones.
Resultsm²
Airflow
Volume flow Q
16141 m³/h
9500 CFM · 4.483 m³/s · 1000 CFM/TR
Discharge zone — unit face
Discharge face area
1.76 m²
Unit footprint W × H — fan-forced
Velocity through face
2.55 m/s
Fan-forced — higher values tolerated
Intake zone — remaining grille
Required free area
1.60 m²
Q ÷ V_intake — open area only (η not applied)
Required gross grille area
2.90 m²
Free area ÷ η (0.55) — size this panel
Intake velocity through free area
2.81 m/s
High — check noise
Total
Total grille area
4.66 m²
Discharge 1.76 m² + Intake 2.90 m²
Grille layout — niche cross-section
Intake grille
2.90 m² gross · 1.60 m² free (η 0.55)
2.90 m² gross · 1.60 m² free (η 0.55)
Baffle
Physical separation — prevents recirculation
Physical separation — prevents recirculation
Discharge face
1.76 m² · 2.55 m/s fan-forced
1.76 m² · 2.55 m/s fan-forced
Total grille
4.66 m²
Calculation trace
Capacity & airflow
Capacity = 9.50 TR = 33.4 kW
Q = 9.50 TR × 1000 CFM/TR = 9500 CFM = 16141 m³/h = 4.483 m³/s
Discharge face
A_discharge = 1.7596 m²
V_discharge = 4.483 ÷ 1.7596 = 2.55 m/s
Intake grille
A_free = 4.483 ÷ 2.81 m/s = 1.5956 m²
A_gross = 1.5956 ÷ η 0.55 = 2.9010 m²
Total grille
A_total = 1.7596 + 2.9010 = 4.6606 m² (50.17 ft²)
VixeldorfAll calculations are engineering estimates. The 1000 CFM/TR rule applies to hot climates (Israel, Middle East). For production drawings, verify with manufacturer catalog airflow. A physical baffle separating intake and discharge zones is mandatory in niche installations to prevent hot-air recirculation.