High CO2 in an Air-Conditioned Office: What Does It Mean Malaysia
High CO2 in an Air-Conditioned Office: What Does It Mean Malaysia
Your office is air-conditioned.
The temperature feels comfortable.
The doors and windows are closed.
But the CO₂ reading keeps increasing.
What does this mean?
One important point is that air-conditioning and ventilation are not necessarily the same thing.
An air-conditioning system can cool indoor air effectively while an occupied room may still require investigation of its ventilation conditions.
For Malaysian offices, meeting rooms and commercial buildings, monitoring CO₂ alongside other indoor environmental parameters can provide useful information.
The TENMARS TM-380 Multi IAQ Monitor measures:
CO₂
PM2.5
PM10
Temperature
Relative humidity
This makes it useful for investigating indoor environments where the problem may involve more than temperature alone.
Why Does CO₂ Increase Indoors?
People continuously produce carbon dioxide through respiration.
As more people occupy an enclosed room, CO₂ can increase.
The actual concentration at a particular time can be influenced by factors such as:
Number of occupants
Room size
Ventilation
Outdoor air exchange
Duration of occupancy
Building operation
This is why CO₂ can change significantly throughout a working day.
Why Can CO₂ Be High When the Air-Conditioning Is On?
A common misunderstanding is:
“The air-conditioning is running, so the room must be well ventilated.”
Not necessarily.
Cooling and ventilation perform different functions.
An air-conditioning system may cool or recirculate indoor air while outdoor-air ventilation depends on the design and operation of the building system.
Therefore, a room can have:
Comfortable temperature + increasing CO₂
at the same time.
Example: A Typical Meeting Room
Imagine a meeting room before a meeting begins.
Only one person is inside.
The CO₂ reading is relatively low.
Then ten people enter and close the door.
The meeting continues for one hour.
Although the air-conditioning keeps the temperature comfortable, CO₂ may gradually increase if ventilation is insufficient relative to occupancy.
This is why meeting rooms are useful locations for CO₂ monitoring.
Why Meeting Rooms Can Be Different from Open Offices
An open office may have:
Larger floor area
More air movement
Lower occupant density
Different ventilation characteristics
A small meeting room may have:
Smaller volume
Closed doors
High temporary occupancy
Long meetings
Therefore, a CO₂ measurement taken in the open office should not automatically be assumed to represent the meeting room.
Portable measurement allows individual rooms to be investigated.
What Does a High CO₂ Reading Tell You?
An elevated CO₂ reading in an occupied room can provide useful information for investigating ventilation relative to occupancy.
However, one reading alone does not automatically identify the exact cause.
Further investigation may need to consider:
Occupancy
Ventilation system operation
Outdoor-air supply
Room usage
HVAC schedules
Building conditions
For professional troubleshooting, measurements should be interpreted in the context of the actual site.
Measure Before, During and After Occupancy
Instead of taking only one reading, try observing how CO₂ changes.
Before Occupancy
Measure the room before people enter.
During Occupancy
Observe the reading as the room becomes occupied.
After Occupancy
Continue monitoring after people leave.
This can reveal a pattern that is much more informative than one spot measurement.
Example Measurement Sequence
A facility team could investigate a meeting room at:
9:00 AM — Empty room
9:15 AM — Meeting begins
9:45 AM — Room occupied for 30 minutes
10:15 AM — Meeting ends
10:45 AM — Room empty again
Comparing these periods can help show how occupancy and ventilation influence CO₂ conditions.
Why Data Recording Helps
Indoor conditions are dynamic.
The problem may occur only:
During afternoon meetings
When a training room is full
During certain HVAC operating periods
When doors remain closed for long periods
The TENMARS TM-380 supports manual and automatic recording, making it useful for observing changes over time.
Does Opening a Door Solve the Problem?
Opening a door may change air movement and CO₂ conditions, but it should not automatically be treated as a complete ventilation solution.
The actual response depends on:
Building design
Adjacent space
Ventilation system
Outdoor conditions
Occupancy
Measurements before and after changes can provide useful information, while the appropriate corrective action should be determined according to the building and HVAC system.
Malaysia Haze Makes the Situation More Complicated
During haze, building operators may want to reduce the entry of outdoor particulate pollution.
This may involve keeping windows and doors closed.
But occupied rooms still need appropriate ventilation.
This creates a practical balance between:
Reducing outdoor particle entry
and
Maintaining indoor ventilation.
This is one reason a multi-parameter monitor can be useful.
Why Measure PM2.5 Together with CO₂?
Imagine a meeting room during haze.
Windows are closed.
An air purifier is operating.
You could observe:
PM2.5 decreasing
while
CO₂ increasing.
If you measure only PM2.5, the room may appear to be improving.
If you measure only CO₂, you will not know the particulate condition.
The two parameters provide different information.
Another Scenario: Low CO₂ but High PM2.5
The opposite can also happen.
A room may receive sufficient outdoor air to keep CO₂ relatively low.
But if outdoor particulate pollution is elevated and filtration is insufficient for the conditions, PM2.5 could still be high.
Therefore:
Low CO₂ does not automatically mean low PM2.5.
Why PM10 Is Useful
The TENMARS TM-380 also measures PM10.
This can be useful when an office or commercial building is affected by:
Construction
Renovation
Dust
Cleaning activities
Outdoor particle infiltration
This gives facility teams another parameter for particulate investigations.
Temperature Is Still Important
Temperature provides important information about thermal comfort and HVAC operation.
But the key lesson is:
A comfortable temperature does not prove that ventilation conditions are satisfactory.
CO₂ should be measured directly when ventilation relative to occupancy is the issue being investigated.
Relative Humidity Adds More Context
The TM-380 also measures relative humidity.
This allows facility teams to observe:
CO₂ + PM2.5 + PM10 + Temperature + Humidity
during the same inspection.
This can be useful when occupants report general discomfort rather than one clearly defined problem.
Where Should CO₂ Be Checked?
Potential office measurement locations include:
Open office areas
Meeting rooms
Conference rooms
Training rooms
Enclosed offices
Reception areas
Measurements should be taken according to the purpose of the investigation and appropriate measurement practice.
Compare Different Rooms
One useful approach is to compare several spaces during similar occupancy conditions.
For example:
Open Office → Small Meeting Room → Large Conference Room → Training Room
If one room consistently behaves differently, facility teams have a clearer location for further investigation.
Who Should Investigate High Office CO₂?
Depending on the building and issue, further investigation may involve:
Facility managers
HVAC contractors
Building maintenance teams
M&E personnel
Environmental professionals
Safety personnel
A portable CO₂/IAQ instrument provides measurement data that can support the troubleshooting process.
TENMARS TM-380 for Office CO₂ Monitoring Malaysia
The TENMARS TM-380 uses an NDIR sensor for CO₂ measurement and combines this with:
PM2.5
PM10
Temperature
Relative humidity
It also supports manual and automatic recording, making it useful for observing how indoor conditions change with occupancy and time.
For Malaysian offices, meeting rooms, commercial buildings and facility management applications, it provides a practical way to investigate whether a comfortable air-conditioned room may still have other indoor environmental conditions requiring attention.
Contact MTM Precision
MTM Precision Sdn. Bhd.
Showroom & Service Centre
No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia
🌐 Website: www.mtmpre.com.my
📧 Email: mtmpre@yahoo.com
📱 WhatsApp: +6016-660 7346
Contact MTM Precision for TENMARS TM-380 Multi IAQ Monitor enquiries in Malaysia.
13 Aug 2026
