Protect seedlings with controlled inward air flow. Tune fans, filters, and vents for stable pressure. Export reports instantly and keep your grow area clean.
| ΔP (Pa) | Leakage area (m²) | Safety factor (%) | Required exhaust (CFM) |
|---|---|---|---|
| 5 | 0.020 | 15 | 91 |
| 8 | 0.015 | 20 | 91 |
| 12 | 0.010 | 10 | 68 |
This calculator models air entering through combined cracks and openings as an orifice. The flow required to maintain a negative pressure is:
A safety factor increases the airflow to account for filter loading, duct losses, and wind-driven leakage changes.
In greenhouses and indoor gardens, negative pressure keeps air moving from clean zones to dirty zones, so pests, spores, and odors are less likely to escape. It also stabilizes intake locations, improving temperature uniformity, CO₂ delivery, and the effectiveness of sticky traps and screening. For propagation areas, inward airflow helps protect tender seedlings from drafts carrying pathogens.
Most plant rooms operate with modest differentials, often 2–15 Pa, because higher values can increase infiltration velocity and dry media near cracks. Use the lowest pressure that still maintains inward door drift, reliable smoke-pencil direction, and consistent filter loading. Separate goals: containment favors higher ΔP, while plant comfort favors stable, gentle airflow.
The calculator links pressure difference to leakage flow using a discharge coefficient and air density. Treat leaks as an equivalent opening area: larger cracks need more fan flow to hold the same ΔP. Seal obvious gaps first; every reduction in leak area lowers required fan power and noise. If doors open frequently, plan for a temporary pressure dip and recovery time.
If air must be scrubbed, place exhaust filters upstream of fans when possible to reduce bypass and prevent fan contamination. Keep intake routes short and protected, and avoid competing exhaust sources like heaters or dehumidifiers that can change the balance. Record filter pressure drop separately from room ΔP, and schedule replacements when airflow falls or odor breakthrough appears.
Verify performance with a manometer at a representative point, away from direct fan jets. If ΔP fluctuates, check loose panels, stuck louvers, blocked prefilters, or wind effects at vents. When humidity rises, confirm exhaust flow, then adjust intake area or fan speed gradually to protect plants and prevent leaf-edge burn. Log readings at lights-on and lights-off, because temperature swings change air density and fan curves. After changes, remeasure, update your baseline, and train staff to close doors promptly every shift.
It means the room air pressure is slightly lower than adjacent spaces, so air flows inward through openings. This supports containment and controlled ventilation when exhaust flow exceeds intake.
Use a differential manometer with one tube inside the room and one outside. Measure away from fans and doors, then average several readings over a minute to smooth pulses.
It is a single opening area that would leak the same airflow as all cracks and gaps combined at a given pressure. It helps translate sealing improvements into airflow and fan-size changes.
For sharp-edged openings, 0.60–0.70 is common. If your leaks are irregular, start with 0.65 and compare predicted airflow with a measured exhaust flow, then adjust Cd to match reality.
Leakage flow depends on density: cooler, denser air needs slightly less volumetric flow to achieve the same pressure. High altitude and warm rooms reduce density, so fans may need more volume.
Seal large leaks, add a dedicated intake path, and use variable fan speed to hold a small stable setpoint. Avoid over-exhausting during dry periods, and monitor substrate moisture near doors and cracks.
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.