NCC Part J — Fan Efficiency Calculator

Minimum fan efficiency at full load · J6D5(2)

Deemed-to-Satisfy

What this checks

Fans, ductwork and duct components forming part of an air-conditioning or mechanical ventilation system must comply with NCC 2022 Section J. This tool returns the minimum fan efficiency at the full-load operating point required under the Deemed-to-Satisfy provision J6D5(2). Enter the system static pressure, installation arrangement, fan type and motor input power.

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Inputs

System static pressure (Pa)

Index-run static pressure at the full-load duty point. Allow for dirty filters and, for an AHU/FCU, the unit's internal pressure losses.

Installation type

Type A
Free inlet · Free outlet Type B
Free inlet · Ducted outlet Type C
Ducted inlet · Free outlet Type D
Ducted inlet · Ducted outlet

Type A/C return static efficiency; type B/D return total efficiency.

Fan type

Fan motor input power, P (kW)

Electrical input power of the fan at the duty point (from manufacturer selection). Only used when static pressure > 200 Pa.

Optional — compliance check

Selected fan's efficiency at duty point (%)

Enter the static (type A/C) or total (type B/D) efficiency of your selected fan to test it against the requirement.

Required minimum efficiency

Minimum required static efficiency

49.5%

η min at full-load operating point

Basis: J6D5(2)(c) · > 200 Pa

Installation typeA · Free inlet · Free outlet

Efficiency basisSTATIC (cat AC)

Fan typeCentrifugal backward-curved

System static pressure400 Pa

Motor input power, P2.82 kW (<10 kW)

Grade N · coeff a · coeff b64 · 4.56 · 10.5

η min = 0.85 × ( a·ln(P) − b + N ) / 100 = 0.85 × ( 4.56·ln(2.82) − 10.5 + 64 ) = 0.85 × ( 4.728 − 10.5 + 64 ) = 49.5 %

Method & references

Systems ≤ 200 Pa — η min = 13 × ln(p) − 30, where p is the system static pressure (Pa). The result is a single static/total efficiency independent of fan type and power. [J6D5(2)(a)]
Systems > 200 Pa — η min = 0.85 × (a × ln(P) − b + N) / 100, where P is the fan motor input power (kW); N from Table J6D5a; a from Table J6D5b; b from Table J6D5c. The 0.85 factor is the NCC 2022 allowance. [J6D5(2)(c)]
Applicability — under J6D5(2)(e) the provision does not apply to fans that need to be explosion-proof. J6D5(5) further exempts: fans in unducted A/C systems < 1000 L/s, smoke-spill fans (unless also used for A/C or ventilation), process-related components, and kitchen exhaust systems. Note that NCC 2022 J6D5 does not set a lower power cut-off; the underlying regression is, however, validated only over roughly 0.125–500 kW motor input power.
Alternative compliance — a fan that fails the component check may still comply via J6D5(1)(b) where the whole system's fan motor power per unit of flow (W per L/s) is lower than a system meeting J6D5(2)–(5) together.
Coefficient and grade values are reproduced from NCC 2022 Volume One Tables J6D5a/b/c (numerically identical to NCC 2019 Tables J5.4a/b/c); the method aligns with EU Commission Regulation No. 327/2011.

This calculator provides guidance and an estimate to help determine fan efficiency requirements. It is not evidence of NCC compliance. Designers must verify all inputs and outputs against the current NCC, the relevant referenced Standards and manufacturer selection data, and apply their own engineering judgement.