Data shows that improving indoor ventilation can reduce the risk of virus transmission, and is recommended by the CDC. But to what level of ventilation is ‘acceptable’ or ‘safe’. How much should it be increased by? In this article, we’ll cover the recommended ventilation rates for offices, homes, schools and hospitals.
Recommended Room Ventilation Rates
In the US, ASHRAE sets the minimum outdoor air ventilation rates for buildings in the ASNI/ASHRAE Standard 62.1 and 62.2 guidelines. These standards specify how much outdoor air should be brought into a room every hour, and is based on occupancy and room size.
The ASHRAE 62.1 (“Ventilation and Acceptable Indoor Air Quality in Residential Buildings”) recommends homes receive no less than 0.35 air changes per hour of outdoor air to ensure adequate indoor air.
For other spaces like offices, shops, and schools, the ASHRAE 62.1 standard doesn’t give a fixed number. Instead, airflow rates based on the size of a room, its use (e.g. school, office, sports arena) and the number of people inside are provided. These can be used to calculate exact airflow requirements for a certain space.
The table below provides a summary for common building types, based on typical room sizes and occupancy rates.
As the ASHRAE 62.1 makes clear, there’s no ‘one size fits all’ ventilation rate for every situation, but the table above gives an approximate guideline which can be used for outdoor air ventilation into a room. If you’re calculating ventilation rates for your own space, you should refer to the ASHRAE 62.1, however the following rules may be helpful as starting points.
Doubling Room Occupancy Means Doubling Ventilation Rate
Ventilation rates are calculated on a per-person basis. If the number of occupants in a room doubles, the required ventilation rate doubles. This rule can be useful for office spaces as the occupancy level changes.
Bigger Spaces Require More Outdoor Air
This rule is simple. Ignoring the number of people in a room, a room that’s 100sqm requires twice as much outdoor air as a room that’s 50sqm.
Reminder: The ASHRAE Ventilation Rates Are Only A Guideline
The ASHRAE Standard is a useful guideline for ventilation rates in homes, offices and other locations. However, there may be some situations where the recommended ventilation rate here is too low. The ASHRAE Standard outlines two of these situations:
- Areas with smokers. In areas with smokers or environmental tobacco smoke, the required ventilation will be higher.
- Areas with sources of harmful emissions. If an area has a high level of harmful emissions such as VOCs, then you may need to increase ventilation further or use an air purifier.
Recommended Ventilation Rates When Dealing with Viruses
The ASHRAE guidelines give general ventilation rates to maintain a comfortable indoor environment. What they don’t cover are situations where a high number of viruses are present. That could be hospitals, or in the context of COVID-19, offices, schools or restaurants with infected people.
For these scenarios, we need to look to the ANSI/ASHRAE/ASHE Standard 170-2017 or the CDC for guidelines. The ASHRAE 170-2017 states a recommended number of outdoor air changes per hour of 2, with the total air changes required varying from 6-12 (depending on the location in the hospital).
|Hospital Area||Minimum Outdoor ACH||Minimum Total ACH|
|Critical and Intensive Care||2||6|
|Airborne Infection Isolation Room||2||12|
Similarly, the CDC recommends 6-12 air changes per hour for airborne infection isolation rooms (AIIB).
If dealing with viruses or other airborne infections, it is therefore recommended to have a higher ventilation rate, in the proximity of 6-12 air changes per hour.
Paddy is the CEO of Smart Air, running operations from Beijing. He has a Masters in aeronautical engineering from Bristol University, UK having specialised in aerodynamics. An advocate for open data, free information and transparent business, he spends his spare time promoting honest business and social enterprise.