Coronavirus · Clean Air · Planner

Air purifier ACH planner

Turn room size, existing ventilation, and purifier CADR into equivalent air changes per hour, lingering-aerosol clearance timing, and a practical answer to the question people actually have: is this setup big enough?

Room and purifier inputs

Results update instantly. Use the button only if you want a shareable URL.

What this page is for

Translate room size and purifier spec sheets into a number people can compare: equivalent ACH.
Check whether one purifier is obviously undersized for a classroom, office bay, or large bedroom.
See how fast lingering aerosols fall after the source leaves, instead of treating airflow as an abstract label.
Estimate how many more matching units would close the gap to your chosen target.

Default example: 4.83 equivalent ACH in a room of 9000.0 ft3, with 1 extra matching unit needed to hit 6.0 ACH.

Read the launch note for this clean-air tool.

Clean-air summary

Clearance timing after the source leaves

Interpretation

How to read equivalent ACH

Range	What it usually means
Below 3 ACH	Usually weak for long shared-air occupancy unless the room is sparsely used or naturally very breezy.
4 to 6 ACH	A common planning band for classrooms, offices, and general shared-air risk reduction.
8+ ACH	Strong clean-air delivery, often useful when occupancy is dense or a room turns over fast between groups.

Scope and limits

This is a room-air planning tool, not a medical risk guarantee.
CADR values are rough real-world planning inputs; noise limits, filter condition, and fan speed still matter.
Clearance timing assumes the source stops adding aerosols. Occupied-room exposure is a different problem from post-event flush-out.
Use it to sanity-check purifier sizing fast, then refine from your actual room and hardware constraints.

Common questions

Short answers for adjacent search queries and first-use questions.

What ACH is usually considered decent for a classroom or shared room?

A common planning band is roughly 4 to 6 equivalent ACH for general shared-air risk reduction, while denser rooms or faster turnover often justify aiming higher.

Does CADR convert directly into ACH?

Not by itself. ACH depends on room volume and the clean-air delivery rate. The same purifier can be strong in a bedroom and weak in a classroom if the room size changes.

What does clearance time on this page mean?

It is the estimated decay time after the source stops adding aerosols. It helps with flush-out thinking, not with guaranteeing safety while people are still sharing the room.