Air path matters more than fan count
Fans need a sensible intake, discharge route and make-up air path. More fans can still underperform if ducting or room geometry blocks the flow.
Electrical calculator · ACH / fan / airflow
Air Changes per Hour Fan Calculator
Estimate airflow required for workshops, drying rooms, stores and warehouses by room volume and target air changes.
For fans, air movers and ventilation equipment selection.
Field notes
Field notes for ACH fan calculator
Practical checks to run before this calculator result turns into a site decision.
Ducting changes the real output
Long flexible duct, crushed bends and reducers can knock capacity down quickly. Use the result as a site sanity check, not a catalogue promise.
Avoid creating a new site hazard
Large fans and air movers add trailing leads, noise, dust movement and sometimes negative pressure. Plan power routes and access before switching on.
FAQ
ACH fan calculator FAQ
Short answers written for UK temporary electrical and HVAC planning work.
What is the ACH fan calculator used for?
Estimate airflow required for workshops, drying rooms, stores and warehouses by room volume and target air changes. It is mainly for temporary HVAC, drying, cooling and site-power planning, especially where a quick pre-check is needed before selecting equipment or changing a temporary setup.
Can this replace BS 7671 design, inspection or testing?
No. It is a competent-person planning aid only. Final decisions still need current BS 7671 requirements, manufacturer data, inspection, testing, risk assessment and the actual site conditions.
What should I verify before acting on the result?
Check room volume, duct length, static pressure, intake and exhaust position, make-up air and the supply available for continuous fan operation. If any assumption is uncertain, use the result as a prompt to investigate rather than as permission to energise.
What does an amber or red result usually mean?
It normally means the margin is weak, an assumption is missing, or the load should be split, staged, moved closer to the supply, reduced or reviewed by a competent electrician before use.
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