Is the Exhaust Fan Sizing Calculator free to use?

Yes. The Exhaust Fan Sizing Calculator is a free browser-based planning calculator from I Love MEP.

Can the Exhaust Fan Sizing Calculator be used for final engineering design?

No. The result is for planning, tender review, and coordination support. Final design must be checked by a qualified engineer against project specifications, authority requirements, and applicable standards.

Does the PDF report replace approved design calculations?

No. The PDF report records inputs, assumptions, warnings, and planning results. It should be reviewed before any construction, procurement, or authority submission decision.

Exhaust Fan Sizing Calculator

A ventilation planning calculator for sizing exhaust fans by air changes or equipment/fixture-based exhaust demand. Includes formulas, sample data, warnings, related tools, and a downloadable MEP report.

Last updated: July 27, 2026

Inputs

Forms are empty on load. Use sample data to preview the workflow or enter your own project values.

Learn more

Formula logic, use cases, assumptions, and limits for this tool.

How this tool helps

Use this to choose a practical exhaust fan capacity where both room-volume ventilation and fixture/equipment exhaust demand matter.

Assumptions and limits

This tool provides a planning-level result. It does not replace detailed engineering design, approved software, manufacturer data, authority requirements, or project specifications.

Typical use cases

Early estimation and tender support.
BOQ sanity checking and technical review.
Site discussion before final engineering verification.
Comparison of alternatives using consistent assumptions.

Result interpretation

Read the recommendation, warning, and confidence sections together. A result without warnings is still not an approval; it only means the entered values did not trigger built-in planning alerts.

Input definitions and typical values

These notes explain what each input means and which values usually produce a more reliable planning result.

Code / standard profile

Selects the planning profile used for conservative defaults. Use the project authority or client standard where known; otherwise use the closest regional profile. Options: GCC project planning, ASHRAE planning, CIBSE planning.

Room length m

Measured length of the route, room, pipe, duct, or cable run. Use the actual equivalent length including bends, fittings, or route offsets where applicable.

Room width m

Measured width of the room, duct, tray, or equipment zone. Use internal clear dimensions when calculating area, velocity, or capacity.

Room height m

Clear internal height or equipment height. Typical occupied rooms are 2.7-3.2 m; warehouses, atria, and plant rooms can be much higher.

Required air changes ACH

Air changes per hour. Offices may be low single digits; toilets, kitchens, exhaust rooms, and plant rooms often need higher ACH by code and use.

Fixtures or equipment count units

Count of fixtures, devices, outlets, or equipment items included in the demand check.

Exhaust per unit CFM/unit

Exhaust airflow assigned per fixture or equipment item. Use authority, manufacturer, or room-use guidance where available.

Fan selection margin %

Design safety margin. 5-15% is common for planning; excessive margin can oversize equipment, cables, pumps, or tanks.

Practical verification checklist

Confirm the selected standard profile is suitable for the project location and authority.
Replace sample values with project drawings, schedules, equipment data, or measured site values.
Review warnings, methodology, and PDF report before using the result outside early planning.
Verify final decisions against official standards, manufacturer data, consultant specifications, and local approvals.

Standards references for verification

For final design checks, verify calculator assumptions against the project documents and official standards bodies such as ASHRAE, NFPA, IEC, IET BS 7671, ICC, and CIBSE.

Calculation methodology

Compares room-volume ACH exhaust with fixture/equipment exhaust and applies the larger value plus margin.

Inputs are treated as planning assumptions. The calculator shows warnings when entered values fall outside practical thresholds or selected standard-profile limits.

View full methodology notes

Version history

v1.3.6-prelaunch: Added methodology, standard profile support, version notes, and direct PDF report download.
v1.3.5: Calculator page added with sample data, warnings, and print-ready report layout.

Stage 2 roadmap: optional saved projects, dashboards, and shared calculation history without forcing login for free use.

Trust and verification

Every result includes assumptions, warning logic, and a downloadable report. Final engineering decisions still need qualified review, local authority approval, manufacturer data, and project specifications.

Worked example

Use the sample data button to load a realistic scenario, then download the PDF report to review inputs, results, methodology, warnings, and disclaimers in one place.