Blauberg ventilation units bring filtered outdoor air into a room and push stale air out, which is the one thing an exhaust fan and an air purifier do not both do. An exhaust fan removes air but draws replacement air from wherever it can. A purifier cleans the air already in the room but does not bring any in. This post sets out what each does in a closed bedroom, and what CO2 can and cannot tell you.
Morion Automation is the authorised Blauberg distributor in India, so we say where we have an interest. We keep to what the sources state, and we give no performance numbers for any unit, because the right unit depends on the room and has to be sized by an engineer.
What happens to the air in a closed bedroom?
People breathe out carbon dioxide, so in a small room with the door and windows closed and the air conditioner running, CO2 builds up as the night goes on. A closed room with no planned air supply has nowhere to send it. That is the case for ventilation: it replaces indoor air with outdoor air.
A small study published in 2016 in the journal Indoor Air looked at this in 14 single-occupancy student dormitory rooms. According to its abstract, measured sleep quality and the perceived freshness of the air were better when CO2 was lower, with average levels of about 660 ppm against about 2,585 ppm. It was a small sample in a particular setting. ASHRAE's policy brief, updated in June 2026, says the evidence for effects of CO2 on sleep patterns and well-being at commonly observed indoor concentrations is inconsistent. So we treat the study as an indication and not as a rule, and we make no claim about sleep or health for any product.
What does an exhaust fan do?
An exhaust fan removes air from a room. That lowers whatever is in that air, including CO2, but the air has to be replaced, and it will come from gaps, doors and other rooms, filtered or not. Outdoor air in many Indian cities carries fine particles, so unfiltered replacement air is a trade-off. A fan also takes the cooled air out of an air-conditioned room with it. Our earlier post on Blauberg and exhaust fans covers this.
What does an air purifier do?
A purifier pulls room air through a filter and returns it. It can reduce particles in that air. It does not bring in outdoor air, and so it does not lower CO2. ASHRAE, the American society for heating, refrigeration and air-conditioning engineers, says in its policy brief on indoor CO2 that CO2 concentration is unaffected by filtration and most other air-cleaning methods. A purifier and ventilation do different jobs.
What does an HRV or ERV do?
An HRV (heat recovery ventilator) or ERV (energy recovery ventilator) is a balanced ventilation unit. One fan draws filtered outdoor air in, another pushes stale air out, and the two streams pass through a core where energy is exchanged without the air mixing. The incoming air arrives closer to room temperature, so the air conditioner has less work to do. An ERV also transfers a share of the moisture.
Our ERV and HRV guide for India lists what to check: airflow, core type, filters, bypass, sound level and controls. Blauberg's home fresh-air series include the Komfort Ultra ME, Komfort EC SB and Komfort GRE EC. Ask us which suits your project and what is available.
| Brings in outdoor air | Filters it | Removes stale air | Lowers CO2 in the room | |
|---|---|---|---|---|
| Exhaust fan | Indirectly, through gaps | No | Yes | Yes, if air is replaced |
| Air purifier | No | Filters room air | No | No |
| HRV or ERV | Yes | Yes | Yes | Yes |
Can CO2 be used as a guide?
Many people buy a CO2 meter and read the number as a verdict. ASHRAE's position is more cautious: its ventilation standards do not include CO2 limits based on health and comfort, and it calls claims of a required threshold, typically 1,000 ppm, incorrect. CO2 is useful as an indicator of how much outdoor air a space is getting, and a rising number in a closed bedroom tells you the room is poorly ventilated. It does not tell you whether the air is clean. Particles and gases need their own measurements.
For a bedroom, the useful questions are: where does fresh air come from, is it filtered, and can the system run quietly all night. Ask the supplier for the sound level in dB(A) of the unit you are choosing.
How do you decide?
- Is the room closed and air-conditioned for long hours? Then a balanced unit with filtered air in suits it better than either a fan or a purifier alone.
- Is the problem dust and smoke from outside? A filter helps, but it only works on air that passes through it.
- Is there somewhere to put the unit and ducts? Ceiling or plant-room space, and access for filters.
- Do you want it to join the building system? Check which interfaces the unit offers and ask us which converter fits a KNX system.
Questions people ask
Does an air purifier lower CO2?
No. A purifier filters air that is already in the room. ASHRAE states that CO2 concentration is unaffected by filtration. Only bringing in outdoor air changes it.
Is an exhaust fan enough for a bedroom?
It removes air, but the replacement air arrives unfiltered and from wherever there is a gap. Whether that is acceptable depends on the air outside and the room.
What is a safe CO2 level in a bedroom?
ASHRAE's ventilation standards do not set a health-based CO2 limit, and we do not give one. Use a CO2 reading as a sign of how well the room is ventilated.
Planning fresh air for a home? Send us the plans and the city and we will suggest Blauberg units: talk to our team. The full guide is here.
Sources checked on 7 November 2026
- ASHRAE, Indoor carbon dioxide policy brief, for CO2 as a ventilation indicator and the effect of filtration.
- Strom-Tejsen et al., The effects of bedroom air quality on sleep and next-day performance, Indoor Air, 2016, for the dormitory study.
- Morion Automation, ERV and HRV in India, for how HRV and ERV units work.
Blauberg ventilation units bring filtered outdoor air into a room and push stale air out, which is the one thing an exhaust fan and an air purifier do not both do. An exhaust fan removes air but draws replacement air from wherever it can. A purifier cleans the air already in the room but does not bring any in. This post sets out what each does in a closed bedroom, and what CO2 can and cannot tell you.
Morion Automation is the authorised Blauberg distributor in India, so we say where we have an interest. We keep to what the sources state, and we give no performance numbers for any unit, because the right unit depends on the room and has to be sized by an engineer.
What happens to the air in a closed bedroom?
People breathe out carbon dioxide, so in a small room with the door and windows closed and the air conditioner running, CO2 builds up as the night goes on. A closed room with no planned air supply has nowhere to send it. That is the case for ventilation: it replaces indoor air with outdoor air.
A small study published in 2016 in the journal Indoor Air looked at this in 14 single-occupancy student dormitory rooms. According to its abstract, measured sleep quality and the perceived freshness of the air were better when CO2 was lower, with average levels of about 660 ppm against about 2,585 ppm. It was a small sample in a particular setting. ASHRAE's policy brief, updated in June 2026, says the evidence for effects of CO2 on sleep patterns and well-being at commonly observed indoor concentrations is inconsistent. So we treat the study as an indication and not as a rule, and we make no claim about sleep or health for any product.
What does an exhaust fan do?
An exhaust fan removes air from a room. That lowers whatever is in that air, including CO2, but the air has to be replaced, and it will come from gaps, doors and other rooms, filtered or not. Outdoor air in many Indian cities carries fine particles, so unfiltered replacement air is a trade-off. A fan also takes the cooled air out of an air-conditioned room with it. Our earlier post on Blauberg and exhaust fans covers this.
What does an air purifier do?
A purifier pulls room air through a filter and returns it. It can reduce particles in that air. It does not bring in outdoor air, and so it does not lower CO2. ASHRAE, the American society for heating, refrigeration and air-conditioning engineers, says in its policy brief on indoor CO2 that CO2 concentration is unaffected by filtration and most other air-cleaning methods. A purifier and ventilation do different jobs.
What does an HRV or ERV do?
An HRV (heat recovery ventilator) or ERV (energy recovery ventilator) is a balanced ventilation unit. One fan draws filtered outdoor air in, another pushes stale air out, and the two streams pass through a core where energy is exchanged without the air mixing. The incoming air arrives closer to room temperature, so the air conditioner has less work to do. An ERV also transfers a share of the moisture.
Our ERV and HRV guide for India lists what to check: airflow, core type, filters, bypass, sound level and controls. Blauberg's home fresh-air series include the Komfort Ultra ME, Komfort EC SB and Komfort GRE EC. Ask us which suits your project and what is available.
| Brings in outdoor air | Filters it | Removes stale air | Lowers CO2 in the room | |
|---|---|---|---|---|
| Exhaust fan | Indirectly, through gaps | No | Yes | Yes, if air is replaced |
| Air purifier | No | Filters room air | No | No |
| HRV or ERV | Yes | Yes | Yes | Yes |
Can CO2 be used as a guide?
Many people buy a CO2 meter and read the number as a verdict. ASHRAE's position is more cautious: its ventilation standards do not include CO2 limits based on health and comfort, and it calls claims of a required threshold, typically 1,000 ppm, incorrect. CO2 is useful as an indicator of how much outdoor air a space is getting, and a rising number in a closed bedroom tells you the room is poorly ventilated. It does not tell you whether the air is clean. Particles and gases need their own measurements.
For a bedroom, the useful questions are: where does fresh air come from, is it filtered, and can the system run quietly all night. Ask the supplier for the sound level in dB(A) of the unit you are choosing.
How do you decide?
- Is the room closed and air-conditioned for long hours? Then a balanced unit with filtered air in suits it better than either a fan or a purifier alone.
- Is the problem dust and smoke from outside? A filter helps, but it only works on air that passes through it.
- Is there somewhere to put the unit and ducts? Ceiling or plant-room space, and access for filters.
- Do you want it to join the building system? Check which interfaces the unit offers and ask us which converter fits a KNX system.
Questions people ask
Does an air purifier lower CO2?
No. A purifier filters air that is already in the room. ASHRAE states that CO2 concentration is unaffected by filtration. Only bringing in outdoor air changes it.
Is an exhaust fan enough for a bedroom?
It removes air, but the replacement air arrives unfiltered and from wherever there is a gap. Whether that is acceptable depends on the air outside and the room.
What is a safe CO2 level in a bedroom?
ASHRAE's ventilation standards do not set a health-based CO2 limit, and we do not give one. Use a CO2 reading as a sign of how well the room is ventilated.
Planning fresh air for a home? Send us the plans and the city and we will suggest Blauberg units: talk to our team. The full guide is here.
Sources checked on 7 November 2026
- ASHRAE, Indoor carbon dioxide policy brief, for CO2 as a ventilation indicator and the effect of filtration.
- Strom-Tejsen et al., The effects of bedroom air quality on sleep and next-day performance, Indoor Air, 2016, for the dormitory study.
- Morion Automation, ERV and HRV in India, for how HRV and ERV units work.
