A practical guide to reading duty points, margins and fan curves — the method the selector on this site uses.
1. Define the duty point, not the maximum values
A fan is specified by one operating point: the airflow the system needs and the static pressure the system opposes at that airflow (coils, filters, ducts, louvres). Catalogue “maximum airflow” is measured at zero pressure and “maximum static pressure” at zero airflow — the two never occur together, so they can only pre-screen candidates. The selector on this site interpolates each model's measured P-Q curve at your airflow and checks that the available pressure is above the required value.
2. Keep a 10–25% pressure margin
Filters load up, coils foul, ducts are rarely as clean as the drawing. A model that just meets the point today stalls in six months. Too much margin is also a cost: the fan runs off its best-efficiency region, draws more power and makes more noise. The selector scores every result on this window and flags margins below 8% as tight.
3. Prefer a model with speed grades in reserve
Multi-speed AC fans and 0–10 V / PWM controlled EC fans have several curves. Meeting the point on a lower grade means you can step up later without changing the fan. The results table shows the grade used and how many higher grades remain.
4. Choose the motor platform for the control need
EC when the airflow varies with load, must be modulated by a BMS, or energy consumption matters — typically about 30% lower consumption than an equivalent AC fan at part load, higher under strongly variable duty (confirm against the load profile). AC for constant duty at the lowest first cost. DC for low-voltage, battery or electronics cooling applications.
5. Verify before ordering
Check the dimensional drawing against the installation space, the inlet conditions (an obstructed inlet costs pressure), the operating temperature range, and the certification required for the market. Then request a quotation with the duty point attached — our engineers confirm the selection and, where needed, propose a better fit.