Restroom Exhaust Sizing Calculator

Design restroom ventilation confidently using dual methods calculate airflow from room volume and target ACH or from fixture counts choose the greater result then get suggested duct diameters and rectangular sizes includes unit toggle diversity sensible defaults and printable summary with estimated velocity checks leak allowance duty cycle options and code note reminders built

1) Space and Ventilation Targets
Common range 8–15 for many restrooms; verify local code.
Optional: impose a code minimum flow.
2) Fixture Method
Percent of fixtures expected on simultaneously.
3) Duct Sizing Targets
Typical exhaust 600–1200 fpm. Balance noise and pressure loss.
FAQs
1) Which method should I use—ACH or fixtures?

Both are shown. Use the governing (larger) value unless a specific code clause dictates otherwise for your project type.

2) What ACH is typical for restrooms?

Designs commonly fall in the 8–15 ACH range. Public spaces or odor‑sensitive areas may justify higher rates. Always check local requirements.

3) Are lavatories included in the fixture method?

Lavatories typically drive supply make‑up air more than exhaust. This tool focuses on exhaust drivers like toilets, urinals, and showers.

4) How do I choose a duct velocity?

Higher velocity reduces duct size but increases pressure drop and noise. 600–1200 fpm is a common range for small exhaust branches.

5) Does the safety allowance replace detailed loss calculations?

No. It is a buffer for leakage and uncertainty. Perform a full pressure loss calculation to size the fan.

6) Can I use this for residential bathrooms?

Yes for preliminary checks. Many dwelling bathrooms use a simple minimum rate per bath. Verify minimums for continuous vs intermittent operation.

7) How do I size make‑up air?

Provide a balanced approach so that exhaust flow is matched by transfer or supply air paths. Avoid excessive negative pressure that can affect doors and traps.

Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.