Size your vent grilles for gardens and greenhouses. Enter airflow targets and preferred face speed. Get instant area, quantity, and velocity results clearly now.
| Scenario | Airflow | Target velocity | Grille size | Free area | Suggested quantity |
|---|---|---|---|---|---|
| Small grow tent exhaust | 200 CFM | 300 ft/min | 10 in × 6 in | 65% | 2 |
| Greenhouse intake with screen | 450 CFM | 250 ft/min | 14 in × 10 in | 55% | 2 |
| Indoor garden exhaust | 700 CFM | 400 ft/min | 16 in × 12 in | 60% | 2 |
| Metric micro-green rack | 500 m³/h | 1.8 m/s | 25 cm × 20 cm | 65% | 2 |
| Large greenhouse bay | 1800 m³/h | 2.2 m/s | 40 cm × 30 cm | 60% | 3 |
Vent openings should match fan delivery, not just duct size. Use measured airflow when possible, because filters, bends, and carbon can reduce flow. For grow tents, aim for steady exchange without harsh drafts on leaves. Greenhouses often need larger inlets to avoid negative pressure that pulls unfiltered air through gaps. When intake and exhaust are balanced, humidity control is smoother and odor control works better. Record readings at different fan speeds for better calibration. Small adjustments can improve comfort and energy use noticeably today.
Face velocity is the air speed through the effective open area. Lower velocities generally mean lower noise, less whistling, and gentler movement across foliage. Higher velocities can be acceptable on exhaust points, but can stress seedlings at intake locations. A common design range is moderate and consistent, then validate by checking fan static pressure and temperature stability during lights-on cycles.
Free area is the percentage of a grille that is truly open after louvers, frame, and insect mesh. Fine screens reduce free area and add pressure loss, so the effective opening may be much smaller than the nominal size. If pests are a concern, select a larger grille or increase quantity, then keep velocity moderate. This reduces clogging risk from dust and pollen.
The required net free area comes from airflow divided by target velocity. The calculator also reports net area per grille, total net area provided, and the achieved face velocity using your selected grille count. If achieved velocity exceeds your target, airflow is being forced through too little open area. Increasing grille size, using a higher free-area model, or adding another grille typically fixes it.
Place intake grilles away from direct spray, soil splash, and fertilizer mist. Keep at least a short straight run behind the grille to limit turbulence and noise. Seal around frames so air uses the intended opening. Inspect screens weekly in dusty seasons and wash gently before buildup hardens. After cleaning, recheck temperatures and humidity to confirm performance remains stable.
Free area is the truly open portion of the grille face after louvers, frame, and mesh. Use the manufacturer value when available, or reduce your estimate when adding insect screen.
Lower velocity reduces noise, whistling, and direct drafts. It also lowers pressure drop across screens, helping fans maintain airflow and keeping plant microclimates more stable.
Increase net free area by choosing a larger grille, selecting a higher free-area model, increasing grille quantity, or improving screen openness. Any of these reduces airflow speed through the opening.
Fine mesh lowers effective free area and increases resistance, so airflow may drop from the fan’s rated value. Compensate with larger grilles, more grilles, or a slightly lower velocity target.
Not always. Intake often benefits from larger net area to keep drafts gentle and reduce dust pull-through. Exhaust can run slightly higher velocity, but avoid excessive restriction that strains the fan.
Use the units you can verify: fan flow from the label or measurement, velocity you prefer, and physical grille dimensions you will install. The calculator converts internally for consistent results.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.