A fan performance curve plots total pressure against air flow at a fixed speed, with power and efficiency curves overlaid. The fan does not choose a single output — it operates where its pressure curve crosses your system resistance curve. Reading that intersection correctly is the difference between a fan that runs efficiently and one that wastes energy or surges.
Always select so the operating point sits near the peak-efficiency region of the curve, not far out on either end. Check the power curve at that point to size the motor with margin, and confirm the point is to the right of any stall region. When you send us your duty flow and pressure, we plot it against the 4-72, GM, 9-26 or 6-30 curves and recommend the model whose best-efficiency point lands closest to your requirement.
