Air Exchange Rate Calculator

Useful calculators

About Air Exchange Rate Calculation

The results are approximate. Before use, verify the calculations against the applicable standards and consult a specialist. The developer is not responsible for the consequences of use without project verification.

The air exchange rate calculator determines the airflow required to ventilate a room based on room volume, the number of air changes per hour or occupancy. The calculation provides a preliminary estimate of the ventilation airflow needed in residential, public and work spaces. Results are given in m³/h and L/s.

Guidelines and recommendations

Calculation based on room volume

Room volume. First, the floor area is multiplied by the room height. Area is entered in m² and height in m, giving the room volume in m³.

V = S × H

Here V is the room volume in m³, S is the area in m² and H is the height in m.

Air change rate. This indicates the volume of air that must pass through the ventilation system in one hour relative to the room volume. For example, a rate of 1 1/h corresponds to an airflow equal to one room volume per hour, while 2 1/h corresponds to two room volumes.

Q_v = V × n

Here Q_v is the airflow in m³/h, V is the room volume in m³ and n is the air change rate in 1/h.

Example. A room with a floor area of 30 m² and a height of 2.8 m has a volume of 84 m³. At an air change rate of 1 1/h, the required airflow is 84 m³/h. Increasing the rate to 2 1/h raises the airflow to 168 m³/h.

Calculation based on occupancy

Airflow per person. The required volume of outdoor air supplied per hour is specified for each person. The total airflow is calculated by multiplying this value by the number of people simultaneously occupying the room.

Q_p = N × q_p

Here Q_p is the total airflow in m³/h, N is the number of people and q_p is the outdoor airflow per person in m³/h.

Default value. The default is 30 m³/h per person. This is a guideline, not a universal regulatory requirement. Depending on the room use and indoor air quality requirements, values of 20, 30, 40 or 60 m³/h per person, or other values, may be used.

Example. If 5 people occupy a room simultaneously and each requires 30 m³/h, the total airflow is 150 m³/h.

Selecting the design airflow

Calculation using one criterion. When only the air change rate or only the number of people is used, the final airflow equals the result of that calculation.

Calculation using two criteria. Both airflows are calculated independently. The higher value is taken as the final airflow because it satisfies both specified requirements.

Q_calc = max(Q_v, Q_p)

Here Q_calc is the design airflow, Q_v is the airflow based on air change rate and Q_p is the airflow based on occupancy.

Comparison example. If the air-change calculation gives 84 m³/h and the occupancy calculation gives 150 m³/h, the final airflow is 150 m³/h. The results are not added together because the two criteria are treated as independent requirements for the same airflow.

Unit conversion and rounding

Airflow conversion. To convert m³/h to litres per second, divide the value in m³/h by 3.6. For example, 150 m³/h corresponds to 41.67 L/s.

Q_l/s = Q_calc / 3.6

Rounding. Airflow and room volume are displayed to two decimal places. Unnecessary trailing zeros are removed. Intermediate calculations are performed without this rounding.

Practical guidelines

Air change rate. For basic ventilation in residential rooms, guideline values of 0.5-1 1/h are often used. In rooms with increased moisture, odours or other pollutants, values of 2-6 1/h or higher may be used. These ranges are not universal regulatory requirements because the necessary air exchange depends on room use and the nature of pollutants.

Number of people. The calculation uses the number of people usually present in the room at the same time. Where occupancy varies, use the expected maximum number of people during the design period.

Calculation assumptions

The air in the room is assumed to be uniformly mixed. Airflow is determined for the entire room volume without dividing it into separate zones.
The calculation assumes steady-state conditions with a constant airflow over one hour.
The floor area and height determine the geometric room volume. No additional volume adjustment factors are applied.
The same airflow per person is assumed for everyone in the room.
No additional safety factors or corrections are applied to the calculated airflow. The calculation multiplier is 1.0.
In the occupancy-based calculation, 0 people gives an airflow of 0 m³/h. If the air change rate is also considered, the final result is the higher of the two airflows.

European standards as references

EN 16798-1:2019. “Energy performance of buildings. Ventilation for buildings. Part 1: Indoor environmental input parameters for design and assessment of energy performance of buildings addressing indoor air quality, thermal environment, lighting and acoustics.” The standard sets out approaches for selecting indoor air quality parameters and indoor environmental categories.

EN 16798-3:2025. “Energy performance of buildings. Ventilation for buildings. Part 3: For non-residential buildings. Performance requirements for ventilation and room-conditioning systems.” The standard addresses requirements for ventilation systems in non-residential buildings and parameters considered in their design.

ISO 17772-1:2017. “Energy performance of buildings. Indoor environmental quality. Part 1: Indoor environmental input parameters for the design and assessment of energy performance of buildings.” The standard provides indoor environmental quality criteria, including air parameters for occupied spaces.

These documents provide references for selecting the initial ventilation requirements. The calculator uses the user-specified air change rate and airflow per person. It does not automatically apply regulatory values for specific room categories.

FAQs

Why do air exchange calculations based on volume and occupancy give different results?

The two methods account for different factors. The air-change calculation depends on room volume and the required frequency of air renewal, while the occupancy calculation depends on the number of people present and the airflow required per person. Therefore, the results can differ substantially even for the same room.

How can I choose an appropriate air change rate?

Choose the air change rate according to room use, intensity of use and indoor air quality requirements. A range of 0.5-1 1/h is often considered for residential rooms, but it is not a universal requirement. If moisture or pollutant emissions are higher, the required air change rate may be significantly higher.

Why does increasing room height increase the required airflow?

At the same floor area, a taller room has a larger volume. If the air change rate remains unchanged, airflow increases in proportion to room height. For example, increasing the height from 2.5 to 3 m raises the airflow calculated from the air change rate by 20%.

What airflow per person should I use?

The value depends on room use, occupant activity and the required indoor air quality. For a preliminary estimate, 30 m³/h per person may be used, while other values, such as 20, 40 or 60 m³/h, can also be considered. For a calculation based on standards, select the airflow according to the applicable requirements and indoor environmental category.

Why is the higher airflow selected instead of adding the two results?

Both methods determine airflow for the same room, but use different criteria. Adding the results could overestimate the ventilation requirement by counting the same air exchange twice. Taking the maximum satisfies both specified criteria without simply adding them together.