Ventilation CFM Calculator
Calculate the exhaust fan size needed to properly ventilate your grow room
Room & Equipment Setup
Enter your grow room dimensions and lighting details
Room Volume: 112 cubic feet
15°C (cool)25°C (warm)35°C (hot)
Ventilation Requirements
For 1x 600W HPS in a 4×4×7ft space
Minimum CFM Required
170
without carbon filter
With Carbon Filter
213
+25% for filter resistance
Recommended Fan
4-inch inline fan
1.5 air exchanges/min
Heat Output
Your 600W HPS setup produces approximately 420 watts (1433 BTU/hr) of heat that must be removed.
Fan CFM by Duct Size
Smaller ducts restrict airflow. If using a smaller duct, you need a higher-rated fan:
| Duct Size | Airflow Efficiency | Fan Rating Needed |
|---|---|---|
| 4-inch | ~50% | 340 CFM fan |
| 6-inch | ~75% | 227 CFM fan |
| 8-inch (recommended) | ~100% | 170 CFM fan |
HPS Heat Management Tips
- • Air-cooled hoods can reduce room heat by 30-40%
- • Place ballast outside the grow space if possible
- • Consider running lights at night when ambient temps are lower
- • Ensure intake is from a cool source (not the same room)
- • LED alternatives produce 50-60% less heat for equivalent output
General Guidelines
- • Aim for 1-3 complete air exchanges per minute
- • Always buy a fan rated higher than minimum—you can use a speed controller
- • Ensure passive intake is 2-4x the size of exhaust opening
- • Negative pressure (exhaust > intake) helps control odors