Why Is My CO2 Monitor Reading High? Malaysia

Why Is My CO2 Monitor Reading High? Malaysia

You place a CO2 monitor in your bedroom, office or meeting room.

At first, the reading looks normal.

After several people enter the room, the number begins increasing.

Or perhaps you wake up in the morning and notice that the overnight CO2 reading was much higher than expected.

Does this mean the CO2 monitor is faulty?

Not necessarily.

A high CO2 reading can be related to occupancy, ventilation, room size, monitor placement and how the space is being used.

Before assuming there is a problem with the instrument, investigate the environment systematically.

1. Check How Many People Are in the Room

People continuously exhale carbon dioxide.

Therefore, occupancy is one of the first things to check.

A room containing:

One person

may behave differently from the same room containing:

Two people.

Five people.

Ten people.

Thirty students.

As occupancy increases, more CO2 is produced.

Whether it accumulates depends partly on how effectively fresh air is exchanged.

2. Check How Long the Room Has Been Occupied

Time matters.

Imagine two people enter a bedroom.

After five minutes, the CO2 reading may not look dramatically different.

But they remain inside for:

One hour.

Three hours.

Six hours.

Eight hours.

If fresh-air exchange is limited, the CO2 trend may continue changing throughout the occupancy period.

This is why bedrooms often produce interesting overnight CO2 data.

3. Check Whether the Windows Are Closed

Many Malaysian homes use air conditioning with windows closed.

Closing windows can reduce one pathway for natural air exchange.

If people remain inside and the room does not receive sufficient fresh air through other means, CO2 may increase.

However, do not automatically assume that every room with closed windows will have the same CO2 condition.

Buildings have different:

Ventilation systems.

Air leakage.

Fresh-air arrangements.

HVAC designs.

Room sizes.

The correct approach is to measure the actual space.

4. Check Whether the Door Is Closed

A bedroom with:

Window closed + door closed

may behave differently from the same bedroom with:

Window closed + door open.

Likewise, a meeting room with the door continuously closed may show a different pattern from one where people frequently enter and leave.

If you are investigating high CO2, record the door condition as part of the test.

5. Don't Assume Air Conditioning Means Fresh Air

This is one of the most common causes of confusion.

The room is cold.

The air conditioner is running.

Therefore, people assume the room must be well ventilated.

But cooling and fresh-air ventilation are different functions.

Many common room air conditioners primarily cool and recirculate indoor air.

The room can therefore remain comfortable while CO2 changes because of occupancy.

6. Check Whether the Monitor Is Too Close to Your Face

Before investigating the building, check the monitor itself.

Where is it located?

If the CO2 monitor is:

Beside your pillow.

Immediately in front of your face.

Directly beside your workstation.

Very close to a meeting participant.

then exhaled breath may influence the reading.

Your breath contains much more CO2 than typical room air.

For general room monitoring, move the instrument to a more representative location according to the manufacturer's guidance.

7. Don't Breathe Directly on the Sensor

This sounds obvious, but it is a useful troubleshooting check.

People sometimes pick up the monitor, look closely at the display and breathe directly toward it.

The reading then increases.

They assume:

“The sensor is unstable.”

But the monitor may simply be detecting the local CO2 from exhaled breath.

Place it back in a representative location and allow it to respond to the surrounding room air.

8. Check Whether the Room Is Small

Room volume matters.

A small enclosed bedroom with two occupants can behave differently from a large open living area with the same two occupants.

Likewise:

A small meeting room with ten people

is different from:

A large conference room with ten people.

When investigating high CO2, consider both occupancy and room size.

9. Check the Ventilation Conditions

Ask:

Is there a fresh-air system?

Is mechanical ventilation operating?

Are outdoor-air dampers or ventilation systems working as intended?

Is the room relying mainly on natural ventilation?

Has the ventilation operating schedule changed?

For commercial buildings, these questions may require investigation by facility or HVAC personnel.

The CO2 monitor can reveal a pattern, but diagnosing the ventilation system itself may require professional assessment.

10. Look at the Trend, Not Just One Number

One high reading is less informative than understanding the complete pattern.

Ask:

What was the reading before people entered?

When did it start increasing?

How quickly did it increase?

Did it stabilise?

What happened when the door opened?

What happened when everyone left?

Did the reading decrease afterward?

Does the same pattern repeat every day?

Trend data can provide much more useful information than one screenshot.

Example: High CO2 in a Bedroom

Suppose your bedroom monitor shows a rising CO2 trend overnight.

Before assuming the instrument is faulty, check:

Number of sleepers.

Bedroom size.

Door position.

Window position.

Air-conditioning operation.

Monitor placement.

Fresh-air ventilation.

Then compare another night under slightly different conditions where practical.

Changing one condition at a time makes the result easier to understand.

Example: High CO2 in a Meeting Room

A meeting room looks normal when empty.

Ten employees enter.

The door closes.

After an hour, CO2 has increased significantly compared with the empty-room condition.

Everyone leaves.

The reading gradually decreases.

If this pattern repeats during multiple meetings, occupancy and ventilation conditions deserve attention.

This is very different from a sensor that displays an unusual value regardless of whether the room is empty or occupied.

Example: High CO2 in a Classroom

A classroom may have low occupancy before school begins.

Students arrive.

Lessons start.

Doors and windows may remain closed because air conditioning is operating.

CO2 begins changing.

During break, students leave.

The reading changes again.

This repeated relationship between occupancy and CO2 can provide useful information for school facility management.

What If the CO2 Reading Is High Even When the Room Is Empty?

This deserves further investigation.

Check whether:

The monitor has recently been moved.

Someone has just been close to the sensor.

The room was recently occupied.

The monitor needs more time to respond to the new environment.

The placement is unusual.

The instrument is being used according to its instructions.

If readings remain questionable, compare the device under known or better-controlled conditions and consult the manufacturer's operating guidance.

Where instrument performance is in doubt, technical checking may be appropriate.

Why Does the Reading Drop When I Open the Door?

Opening a door can change air exchange between the room and surrounding space.

If the surrounding air has lower CO2, the room reading may begin decreasing.

The rate of change depends on actual airflow and building conditions.

This can be useful information when investigating how the room behaves.

However, opening a door once is not a complete ventilation assessment.

Use repeated observations where appropriate.

Why Does the Reading Drop When Everyone Leaves?

When occupants leave, one major source of indoor CO2 generation is removed.

If ventilation continues, the accumulated CO2 may gradually be diluted.

This creates a common pattern:

People enter → CO2 increases

People leave → CO2 decreases

If you repeatedly observe this relationship, it provides useful evidence about the role of occupancy.

Why Is CO2 Higher in the Morning?

For bedrooms, the answer may be related to overnight occupancy.

The room has been occupied continuously for many hours.

Windows and doors may have remained closed.

By morning, the CO2 condition can therefore be different from the condition before bedtime.

This is exactly why overnight historical monitoring is more informative than checking the bedroom only during the afternoon when nobody is inside.

Does an Air Purifier Fix High CO2?

Do not assume so.

A typical particulate air purifier is mainly intended to remove airborne particles.

It may reduce:

PM2.5.

Dust.

Smoke particles.

Other filterable particulate matter.

CO2 is a gas associated strongly with occupancy and ventilation.

Therefore, a room can simultaneously have:

Low PM2.5

and:

Increasing CO2

The air purifier may be working correctly even though the CO2 reading remains high.

What About Haze?

Haze makes indoor air management more complicated.

When outdoor PM2.5 is elevated, people may:

Close windows.

Close doors.

Operate air conditioning.

Operate air purifiers.

These actions may help manage particulate entry under suitable conditions.

However, if several people remain inside an enclosed room, CO2 should be considered separately.

This is one reason monitoring both PM2.5 and CO2 can be useful in Malaysia.

Could the CO2 Monitor Be Wrong?

Instrument problems are possible, but do not make this your first assumption.

Start with basic checks:

Is the monitor positioned correctly?

Has it had enough time to respond?

Is someone breathing directly near it?

Does the reading change logically with occupancy?

Does it decrease after the room becomes empty or ventilation conditions change?

Are you following the manufacturer's instructions?

If the readings remain inconsistent or unreasonable, further instrument checking may be warranted.

Don't Compare Two CO2 Monitors Carelessly

Suppose you have two monitors.

Monitor A is beside the window.

Monitor B is beside a person.

They show different readings.

That does not automatically prove one instrument is wrong.

For a meaningful comparison, place them under similar conditions and allow appropriate response time.

Sensor specifications, response characteristics and calibration can also differ between instruments.

Why Temtop M10+ Helps with Troubleshooting

The Temtop M10+ provides more than CO2 monitoring.

It can monitor parameters including:

CO2

PM2.5

TVOC

AQI

Temperature

Humidity

This helps users see whether several indoor conditions are changing together.

For example:

CO2 increases while PM2.5 stays low.

PM2.5 falls after an air purifier starts.

Temperature falls after the air conditioner starts.

Humidity changes throughout the night.

TVOC changes after new furniture is introduced.

This broader information can help users better understand what is happening inside the room.

A Simple Troubleshooting Checklist

If your CO2 monitor shows a high reading, check:

Occupancy — How many people are inside?

Duration — How long have they been there?

Room size — Is the room small and enclosed?

Windows — Open or closed?

Door — Open or closed?

Ventilation — Is fresh air being supplied?

Air conditioning — Is it mainly cooling and recirculating air?

Monitor location — Is it beside someone's face?

Trend — Is the reading increasing gradually?

Recovery — Does it decrease after occupants leave?

This checklist can resolve many common misunderstandings before concluding that the instrument itself has a problem.

When Is a Professional Assessment Needed?

A general-purpose indoor air quality monitor is useful for:

Screening.

Trend monitoring.

Comparing rooms.

Observing occupancy patterns.

Investigating everyday indoor environmental questions.

It does not automatically replace a formal indoor air quality or ventilation assessment.

For workplaces, commercial buildings or situations requiring regulatory or professional evaluation, appropriate procedures, instruments and qualified professionals may be required.

Why Is My CO2 Monitor Reading High?

A high CO2 reading does not automatically mean the monitor is faulty.

Possible explanations include:

More occupants

Long occupancy duration

Closed room conditions

Insufficient fresh-air exchange for the occupancy

Small room volume

Monitor too close to exhaled breath

Placement near an unusual local environment

Start with the room and the measurement setup.

Then examine the trend.

A useful troubleshooting approach is:

Check placement → Check occupancy → Check ventilation conditions → Observe the trend → Change one condition → Compare again

For Malaysian users who want to monitor CO2 together with PM2.5, TVOC, temperature and humidity, the Temtop M10+ provides a convenient way to observe multiple aspects of the indoor environment.

Contact MTM Precision

MTM Precision Sdn. Bhd. (744811-A)

Showroom & Service Centre

No. 29-1 & 29-2, Jalan Bandar 18,

Pusat Bandar Puchong,

47160 Puchong, Selangor, Malaysia

Telephone: +603-8080 7172

WhatsApp: +6016-660 7346

Email: mtmpre@yahoo.com / enquiry@mtmpre.com.my

Website: www.mtmpre.com.my

Contact MTM Precision for Temtop M10+ CO2 Monitor Malaysia, quotation and assistance selecting indoor air quality monitoring equipment for homes, bedrooms, offices, meeting rooms and classrooms.