ᐅ How many cubic meters per hour do I need for good indoor air quality?

Hello everyone,

I have read a lot about controlled residential ventilation with heat recovery, but I still don’t fully understand the following:

How many cubic meters per hour (m³/h) of supply air are needed to ensure good, continuously fresh air in the various rooms, especially in the bedrooms throughout the entire night?

Here are my rooms with their typical usage and sizes. Maybe you have specific practical experience or calculation values:

Upstairs:
1. Parents’ bedroom (2 persons, 18 m² (194 ft²), 285 cm (9 ft 4 in) ceiling height)
2. Child’s bedroom (1 child, 18 m² (194 ft²), 285 cm (9 ft 4 in) ceiling height)
3. Study room (for 1 person, 10 m² (108 ft²), 285 cm (9 ft 4 in) ceiling height)

Downstairs:
4. Guest room (designed for 2 persons, 11 m² (118 ft²), 255 cm (8 ft 4 in) ceiling height)
5. Living room with an open L-shaped kitchen (ventilation should cover all 4 family members and possibly guests, total 55 m² (592 ft²), 255 cm (8 ft 4 in) ceiling height)

So far, I have read various recommendations ranging from 20 to 30 m³/h per person. But are these values intended for the respective person’s room?

Does that mean, for example, 2 x 30 m³/h = 60 m³/h for the parents’ bedroom?
And 4 x 30 m³/h = 120 m³/h for the living room?

Others calculate based on the room volume, but does this approach sufficiently consider the intensity of use?

What practical values or experiences do you have?

I want to ensure there is always good, fresh air in the bedrooms. The same applies to the children’s rooms as well as the “large” living room with the open kitchen. Especially in the living room, I am unsure what the appropriate air exchange rate in cubic meters per hour should be to adequately serve 4 adult family members plus occasional guests.

I hope you can help shed some light on this ;-)

Thanks in advance!

The minimum hygienic air exchange rate is 0.3 per hour. The design typically uses 0.5 per hour.
There is also a standard that bases the planning on the number of occupants, and 0.5 per hour works well there too. The rate only decreases when a relatively large space has few people.
What is the ventilated volume you have? Keep in mind that transfer areas are included in the calculation.

Thank you for your quick response 🙂, but unfortunately, I still don’t fully understand it...

Alex85 schrieb:
The minimum hygienic air exchange rate is 0.3/h. Planning is usually done with 0.5/h. There is also a standard for planning based on the number of occupants, and 0.5/h generally works well there as well. It only decreases when a relatively large room is used by only a few people.

I have read about this calculation too. However, my question is whether the actual room usage is sufficiently taken into account. Here is my thought process:

In the master bedroom, 2 adults sleep in 51.3 m³ of space (18 m² x 285 cm ceiling height). Assuming an air exchange rate of 0.3, this room would need to be ventilated with 15.39 m³/h (51.3 m³ x 0.3).

What I don’t know— and where I lack practical experience—is how much used air (in m³) 2 adults produce per hour. If the used air produced exceeds the fresh air supplied to the room, the indoor air quality will worsen hour by hour. And obviously, that should not happen.

Therefore, I find it difficult to determine the necessary air exchange based solely on an abstract air exchange rate. It may work well for large rooms with few occupants, but what about small rooms with many occupants? (For example, our guest room for 2 people, which is only 11 m².)

That is exactly the point where I don’t understand the calculations… The result should always be consistently “perfect, fresh” indoor air.

Alex85 schrieb:
What ventilated volume do you have? Keep in mind that air overflow areas should also be included in the calculation.

Overall, our house has a total volume of 501 m³.

I actually don’t understand the calculation based on room volume. Our children’s rooms each have about 27 m² (290 ft²) or 67 m³ (2,366 ft³) and basically only use passive ventilation through Velux window vents and "Regelair." That is completely sufficient and probably results in much lower air exchange rates than the suggested 0.3–0.5 air changes per hour.

How much air does a person “use” during the night?
You can estimate it. The average tidal volume is about 500ml (0.5 liters), more precisely 6ml per kilogram of body weight, and 12-15 breaths per minute, usually fewer during sleep.
But the more important question is how much water vapor does the person release into the air, how much O2 is consumed, and how much CO2 is produced. The breath is not taken completely from the room air, and oxygen is not removed 100% from the inhaled air.
Also, with fever, these calculations do not apply accurately.
So it’s better to rely on the calculations of an experienced ventilation specialist, or you might get caught up in a detail and never finish.
Best regards, Daniel

Daniel-Sp schrieb:
Better rely on the calculation of an experienced ventilation specialist, otherwise you’ll get lost in details and never finish.

I agree with that.

Christian NW schrieb:
Some base it on room volume, but is the usage intensity adequately taken into account here?

Usage intensity is actually the only factor you can exclude from this whole confusion—simply because the calculation is meant to work for the “maximum load.” That means, for example, in a double bedroom even during the hours when both shift workers are asleep at the same time, or in the living room with the entire family and possibly guests as well.

Basically, you breathe more heavily during physical activity (so the least while lying down and sleeping, less when sitting, and more when moving around, etc.). Digestion isn’t consistent in every hour either—so to simplify your calculation, just assume you’re not constantly eating heavy meals like broad beans and sour milk cheese with onion ;-)

Thermal airflows move air, so it’s not equally dense at all heights. Gases have different weights and can “gather” closer to the floor. Therefore, even your lying height influences the calculation. Now imagine your lungs as a pump that pushes your exhaled air into the room: your lung volume remains the same regardless of room size (and in that sense, its spring rate), so it “pumps” with relatively different strength.

Does this roughly illustrate the wisdom of the advice not to get too worked up over these details?

Just as there’s the “average man of 95 percent” and the “conventional retiree,” there is surely a standard homeowner profile according to building regulations that is close to your situation. Their measured values have likely been included in approximate values as well as computer simulations ;-)

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