How much fresh air does your room need? Check in 5 seconds
The bedroom feels "heavy" in the morning. Focus drops at the office in the afternoon. The bathroom mirror stays fogged for an hour after a shower. Same root cause: not enough fresh air relative to what is happening in the room.
Enter the room dimensions (length, width, height), the number of people, and pick the room type (bedroom, living room, office, kitchen, bathroom, workshop, gym, classroom). The calculator shows how many cubic meters of fresh air per hour should enter the room to keep a comfortable indoor climate.
We use the EN 16798-1 and ASHRAE 62.1 standards. Advanced mode lets you enter your own ACH value or change the per-person rate when you have specific guidance from a designer.
How to use it
- Pick the room type from the list: bedroom, living room, office, kitchen, bathroom, workshop, gym, classroom. Each type has its own suggested air-change rate and per-person flow rate based on the standards.
- Enter the room dimensions in meters: length, width, height. Default: a room of 4 × 3 × 2.7 m. You can also switch to direct volume input in cubic meters if you have it from a floor plan.
- Enter the number of people typically present in the room. Bedroom: usually 1-2. Office: depends on workstations. Classroom: 25-30.
- The result shows the required airflow in m³/h (cubic meters per hour), rounded to the nearest 10. Next to it you get a converter to l/s (liters per second), since some heat-recovery units use that unit.
- Below the result you see the calculation breakdown: how much comes from volume × air-change rate, and how much from people × per-person rate. The larger of the two wins.
- Switch on advanced mode (toggle at the top) to override the standard values: enter your own ACH or your own per-person flow rate. For kitchens and bathrooms an extra option appears to add local extraction (cooker hood, bathroom fan).
- The "Time to comfort drop" card shows how many hours without fresh air it takes for CO₂ to reach the level where focus typically drops. This is a rough guide to help you understand the scale, not medical advice.
When this is useful
Six typical situations where this calculator gives you a concrete number instead of a vague feeling:
- Planning a heat-recovery system at home. You are designing an apartment or a house and the installer asks about the unit capacity. You add up the airflows for every room (bedrooms, living, office, kitchen, bathrooms) and you know the size of unit to order. Without a calculator people guess or just "take the same one as the neighbor".
- Checking whether the cooker hood is big enough. You are buying a new hood, the spec says "600 m³/h". You check how much you actually need for your kitchen with two people cooking: the standard is 70 m³/h continuous extraction plus the volume air change. Now you know whether the hood is enough or you need a stronger one.
- Deciding whether the bathroom fan should be automatic. The bathroom mirror fogs for an hour after a shower. You check that at 6 air changes per hour the required flow is a few dozen cubic meters per hour. You know what fan to pick and whether to run it manually or with a humidity sensor.
- Setting up a home office. You work 8 hours in a 3 × 3 meter room. You check that for a single person you need about 30-50 m³/h, so cracking a window for trickle ventilation or installing a trickle vent is enough. No panic, no spending several thousand on a central system.
- Checking a meeting room / classroom / gym. You rent a room for a 20-person workshop. You check that 20 people × 30 m³/h means 600 m³/h of ventilation. Now you know whether the venue has real mechanical ventilation or "fresh air" just means "open the window".
- Telling building management that ventilation does not work. You live in an apartment block, the air feels stuffy. You enter the apartment's parameters, you get concrete numbers from the standard, and you take them to the building manager. A number beats "it feels off" every time.
For the rest of the energy picture: size the boiler / heat pump in the heating power calculator, and check current tariffs in the live electricity prices feed before sizing the HRV.