Required section size
A section for your flow rate and target velocity — without "recommended" numbers
Required section
You set the target velocity — no “recommended velocity” is filled in.
Free-area mode (v_free + k_open)
—м²
Minimum height at this width— мм → — мм
Minimum width at this height— мм → — мм
Enter the flow rate and target velocity. Example: Q=7200, v=3 → A≈0.667 m²; at W=1000 → H_min≈667 mm.
## Method
```text
A_req = Q / (3600 × v_target) [m²]
with W fixed: H_min = 1000 × A_req / W [mm] (rounded up)
with H fixed: W_min = 1000 × A_req / H [mm] (rounded up)
documented free-area mode (both values entered by you):
A_req = Q / (3600 × v_free_target × k_open)
```
## Worked example
Q = 7200 m³/h, v_target = 3 m/s → A_req ≈ 0.667 m². With W fixed at 1000 mm → H_min ≈ 666.7 mm → **667 mm** (rounded up). This is the geometric minimum, not an existing standard size: matching it against the manufacturer size ranges is a separate step.
## Limitations
- The target velocity is your design decision: the tool does not substitute "recommended velocities" and does not check allowability for a model.
- Rounding up gives the geometric minimum; the actual dimensions come from the manufacturer size ranges.
- The v_free + k_open mode works only when both values are entered.