Sizing air purifiers for science labs and libraries, not just classrooms

Key takeaways

• Science labs often have different ventilation setups than standard classrooms, which changes how an air purifier should be sized.
• Libraries see longer individual dwell times than a timetabled classroom, even with lower average headcount at any one moment.
• Apply the CADR formula separately to each room type using its own floor area and realistic occupancy.
• Coordinating sizing across a department or wing avoids inconsistent, room-by-room guesswork.
• A department-wide survey is worth requesting when a school has many different room types to size at once.

Why a science lab's ventilation setup differs from a classroom

Many science labs are built with dedicated extraction points, fume cupboards or additional exhaust ventilation to handle fumes from experiments, which a standard classroom simply does not have. This existing ventilation setup changes the baseline air quality picture before an air purifier is even considered.

A lab also tends to have a more varied occupancy pattern than a timetabled classroom, sometimes empty, sometimes full for a double period of practical work. Fixed lab furniture, benches, sinks and storage cupboards can also affect how freely air circulates compared with an open classroom layout.

Treating a lab as just a classroom with different furniture risks missing these differences. Its existing extraction, occupancy pattern and layout all factor into how an air purifier should be sized and placed within the room.

Library dwell times versus a standard timetabled classroom

A standard classroom follows a timetable, with students moving in and out as periods change throughout the day. A library often works differently, with students settling in for extended independent study or free periods, sometimes staying well beyond a single class period's length.

Average headcount in a library at any given moment might be lower than a full classroom, but the individual dwell time per student is frequently longer. Someone reading or studying at the same desk for an extended stretch shares that immediate air space for longer than a student moving between timetabled classes.

This combination, lower average density but longer individual exposure, is a different profile from a standard classroom and argues for its own sizing calculation rather than reusing the classroom figure across the board.

Applying the CADR formula to each room type separately

The underlying sizing method stays consistent: required clean-air delivery rate, in cubic metres per hour, equals floor area in square metres multiplied by ceiling height in metres multiplied by a target air changes per hour figure. What changes between room types is the floor area, ceiling height, which can vary meaningfully in a lab with high benches or a library with tall shelving, and the appropriate air changes per hour target.

Offices and similar higher-occupancy spaces are generally sized around four to five air changes per hour, and a busy classroom, lab or library often fits within this same range rather than the lower home target. Run each room's actual dimensions through our size calculator individually, since a lab and a library rarely share the same floor area or ceiling height even within the same building.

Coordinating sizing across a whole department or wing

Once individual rooms are sized, it helps to look at the results across a whole department or wing rather than treating each room as an isolated purchase decision. A science wing with several labs of similar size might standardise on one recommended unit, while a library, being a different shape and use pattern entirely, gets its own separate recommendation.

This coordinated approach also simplifies procurement and servicing later, since a school managing a consistent small set of unit types across similar rooms has an easier time than one managing a dozen different models bought individually over several years.

Keep a simple record of each room's floor area, target air changes per hour and recommended unit, so future facilities decisions build on documented figures rather than starting from scratch each time.

Getting a department-wide survey

For a school with several distinct room types to size, a department-wide survey generally produces a more reliable outcome than working from floor plans and specification sheets alone. A survey accounts for real ceiling height variation, existing extraction in labs, and actual furniture layout in libraries, all of which affect how well a given unit's airflow performs in practice.

This is particularly useful when a parent board or school leadership is asking about air quality standards across the whole campus, since a documented, room-by-room survey gives a consistent answer rather than a set of individually justified guesses.

Request a free room-by-room Air Report and we will work through your labs, library and any other rooms you want included as part of the same visit.

Next step

Run each room's dimensions through our free Air Purifier Size Calculator, then request a department-wide survey to confirm the full picture.

Frequently asked

Does a science lab need different air purifier sizing from a classroom?

Yes, science labs often have existing extraction or fume cupboard ventilation that a standard classroom does not, along with fixed furniture and a more variable occupancy pattern. These differences change the baseline air quality picture and should factor into how a lab's air purifier is sized and placed, rather than reusing a standard classroom figure.

Do libraries need different sizing given longer dwell times?

Often yes, since students in a library frequently stay at the same desk for longer stretches than a timetabled class period, even though average headcount at any given moment may be lower. This combination of lower density but longer individual dwell time argues for sizing the library separately from a standard classroom.

Can sizing be coordinated across a whole department at once?

Yes, once individual rooms are sized using the clean-air delivery rate formula, reviewing the results together across a department or wing often reveals where similar rooms can standardise on the same unit. This simplifies both procurement and future servicing compared with treating each room as an isolated decision.

Related reading

• How Many Air Purifiers Does Your Office Need?