Room details
Formula used
The calculator sizes airflow using air changes per hour (ACH) and room volume. First, compute room volume. Then compute required flow:
- Flow (m3/h) = Volume (m3) × ACH
- Flow (CFM) = Flow (m3/h) ÷ 1.699
Next, apply an adjustment multiplier to cover real-world losses: Multiplier = (1 + safety%) × layout factor × (1 + aging%).
Per-unit airflow is the total airflow divided by the number of purifiers. Coverage is estimated from airflow, ceiling height, and your ACH target.
How to use this calculator
- Select your unit system and enter length, width, and height.
- Choose a target ACH based on dust, smoke, or odor levels.
- Set how many purifiers you want to run in the space.
- Add safety and aging margins if conditions are harsh.
- Click Calculate, then compare per-unit airflow to purifier ratings.
Example data table
| Space | Dimensions | Target ACH | Purifiers | Recommended total airflow |
|---|---|---|---|---|
| Seedling shelf corner | 2.0 × 1.5 × 2.4 m | 6 | 1 | ~ 52 m3/h |
| Potting shed | 3.0 × 3.0 × 2.4 m | 5 | 1 | ~ 108 m3/h |
| Small grow room | 2.4 × 2.4 × 2.4 m | 8 | 2 | ~ 110 m3/h |
| Workshop bay | 12 × 10 × 8 ft | 6 | 2 | ~ 407 CFM |
| Garage greenhouse area | 20 × 12 × 9 ft | 5 | 2 | ~ 530 CFM |
Why sizing matters
Gardening sheds, potting rooms, and indoor grow spaces release dust from soil, coco, perlite, and amendments. If capacity is low, particles settle on leaves, lights, and sensors, and odors linger after mixing nutrients. If capacity is excessive, energy use rises and drafts can dry seedlings. Sizing from volume and air changes per hour gives a repeatable target.
ACH and airflow ratings
Air changes per hour (ACH) describes how many room volumes pass through the purifier each hour. The calculator multiplies room volume by your selected ACH and converts the result into m3/h and CFM. Match the per‑unit airflow to purifier ratings to compare models. Typical targets are 4–6 ACH for light use, 6–8 for dusty work, and 8–10 for smoke or sensitivity.
Real-world adjustment factors
Real spaces behave differently than empty boxes. Benches, shelves, tents, and corners create dead zones and short‑circuit paths where clean air leaves before mixing. The safety margin adds reserve for door opening and leakage. The layout factor raises airflow when obstacles block circulation. The filter aging margin accounts for reduced flow as media loads with dust, helping performance stay near the target between cleanings.
Placement and operating strategy
Place the intake near the dust source and keep the outlet aimed across space, not into a wall. Avoid blowing onto plants to reduce dehydration and transpiration. Two smaller units can improve mixing and reduce noise by running at lower speeds. Operate at the calculated setting during active tasks, then step down once the space clears. Increase margins if you open doors often.
Maintenance and verification
Performance depends on clean filters and unobstructed grills. Vacuum or wash prefilters on a schedule and replace main filters when pressure rises or odors return. After setup, verify improvements within a few hours at the chosen speed. If dust persists, raise ACH, adjust placement, or add another unit. Recalculate whenever you change room size, add shelving, seal leaks, or move stations.
FAQs
What ACH should I choose for a potting shed?
Start with 5 ACH for general dust. Use 6–8 ACH if you mix dry soil, sand, or perlite often. For smoke or strong odors, consider 8–10 ACH.
Is CADR the same as CFM?
CADR is a performance rating tied to particle removal and is commonly reported in CFM. If a unit lists CADR and airflow, use CADR as the safer sizing number.
Why does the calculator include a filter aging margin?
As filters load, airflow drops and the fan works harder. Adding an aging margin helps ensure you still meet your target airflow between filter changes, especially in dusty gardening areas.
Should I size for the whole room or just a grow tent?
If the purifier is inside the tent, size for the tent volume. If the purifier is outside and cleans surrounding air, size for the room volume that supplies the tent.
Can I use two smaller purifiers instead of one large unit?
Yes. Two units can improve circulation and reduce dead zones. They also often run quieter at lower speeds while delivering the same combined airflow shown in the results.
How often should I recalculate purifier size?
Recalculate when you change dimensions, add shelving, seal leaks, or switch activities. It is also smart after seasonal changes if doors stay open more often.