Why Is My Indoor CO2 So High? Common Causes & Temtop C1+ Troubleshooting Guide Malaysia

Why Is My Indoor CO2 So High? Common Causes & Temtop C1+ Troubleshooting Guide Malaysia

You switch on your CO₂ monitor.

The reading looks normal.

Thirty minutes later, it is higher.

An hour later, it has increased again.

The natural question is:

“Why is my indoor CO₂ so high?”

In many occupied indoor spaces, increasing carbon dioxide (CO₂) can be related to a straightforward combination:

People are generating CO₂ while the room is not exchanging air quickly enough to keep the concentration near its starting level.

But occupancy is not the only factor worth checking.

Room size, ventilation, measurement position, HVAC operation and other CO₂ sources can all affect the result.

The Temtop C1+ CO2 Monitor can help users investigate these patterns by measuring CO₂, temperature and relative humidity and recording changes over time.

Quick Answer: Why Does Indoor CO₂ Increase?

Common reasons include:

More people entering the room

Doors and windows remaining closed

Limited outdoor-air ventilation

Small room volume

Long occupancy periods

Changes in HVAC or ventilation operation

Poor monitor placement

Nearby combustion or process-related CO₂ sources

Often, several factors occur simultaneously.

The most useful approach is not to panic over one reading.

Investigate the pattern.

Cause 1: People Are Inside the Room

Humans continuously generate CO₂ through respiration.

One person inside a large room may have a relatively small effect.

Now place:

10 people

20 people

or

30 people

inside an enclosed space.

CO₂ generation increases.

This is why CO₂ commonly changes in:

Meeting rooms

Classrooms

Training rooms

Restaurants

Gyms

Clinics

and other high-occupancy spaces.

Cause 2: The Room Has Been Occupied for a Long Time

Duration matters.

Consider a small home office.

9:00 AM

One person enters.

9:15 AM

Little time has passed.

11:00 AM

The room has been continuously occupied for two hours.

1:00 PM

Four hours have passed.

The CO₂ reading at 9:15 AM may therefore tell a very different story from the reading several hours later.

Do not judge a room only from the first few minutes of occupancy.

Cause 3: Doors and Windows Are Closed

This is particularly relevant in Malaysia.

People often close windows because of:

Air conditioning

Outdoor heat

Humidity

Rain

Noise

Traffic pollution

Security

or

Haze.

Closed windows are not automatically a problem—the building may have a mechanical outdoor-air ventilation system.

But if outdoor-air exchange is limited, occupant-generated CO₂ can accumulate.

Cause 4: Air Conditioning Is Running, But CO₂ Still Rises

This often surprises users.

They think:

“The air conditioner is ON, so why is CO₂ increasing?”

Because:

Cooling and ventilation are different functions.

An air conditioner can make the room colder.

That does not automatically mean occupant-generated CO₂ is being removed at the required rate.

The actual result depends on the building and HVAC system.

Therefore:

Cold air ≠ proof of low CO₂.

Measure CO₂ directly.

Cause 5: The Room Is Small

Room volume matters.

Compare:

Room A

Large open office with five people.

Room B

Small meeting room with five people.

The same number of occupants does not necessarily produce the same CO₂ pattern.

Room volume, ventilation and airflow all influence the result.

This is why small enclosed spaces often deserve particular attention.

Cause 6: Occupancy Suddenly Increased

CO₂ can change quickly when occupancy changes.

Imagine a conference room:

8:45 AM → Empty

9:00 AM → 5 people

9:15 AM → 20 people

9:30 AM → 30 people

If ventilation conditions remain unchanged while occupancy rises sharply, the CO₂ trend may change.

Historical data can help connect these events.

Cause 7: The Ventilation System Is Not Operating the Same Way

A room may behave differently at different times.

For example:

Ventilation schedule changes

Equipment is switched off after certain hours

A fan stops operating

Doors that normally remain open are closed

Building operating mode changes

If CO₂ is unexpectedly higher on certain days or at certain times, investigate what else changed.

Cause 8: The Monitor Is Too Close to You

Before concluding that the entire room has very high CO₂, check the monitor position.

If the C1+ is:

directly beside your face

next to your pillow

immediately in front of your desk

or

in the path of your exhaled breath,

local breathing can influence the reading.

Move it to a more representative location and compare.

Cause 9: The Monitor Is in a Poor Airflow Location

Placement near:

Doors

Windows

Air-conditioning outlets

Ventilation supplies

can produce readings influenced by local airflow.

The objective for general room monitoring is usually to measure a representative occupied-zone condition.

A strange reading can sometimes be a placement problem rather than a room-wide problem.

Cause 10: There May Be Another CO₂ Source

Occupants are not the only possible CO₂ source.

Depending on the environment, combustion and certain processes can generate CO₂.

Possible examples can include:

Cooking

Fuel-burning equipment

Combustion appliances

Industrial processes

If the reading seems inconsistent with occupancy, investigate whether another source may be present.

Do not automatically assume every CO₂ increase is caused by people.

Why Does CO₂ Increase at Night?

Bedrooms are a common example.

Two people enter the room.

The windows close.

The door closes.

The air conditioner operates.

They sleep for seven or eight hours.

During that period, both occupants continue generating CO₂ through respiration.

If air exchange is limited, the overnight CO₂ trend may gradually increase.

This is why overnight historical monitoring is more informative than checking only before bedtime.

Why Is My Bedroom CO₂ High in the Morning?

The morning reading reflects what happened during several hours of occupancy.

Ask:

How many people slept in the room?

Were doors/windows closed?

What was the starting CO₂?

Did CO₂ rise gradually or suddenly?

Did it stabilise?

What happened when the door opened in the morning?

The shape of the graph can provide clues.

Why Is Office CO₂ High in the Afternoon?

Office occupancy often accumulates over many hours.

A morning reading may be relatively low.

By afternoon:

More employees may be present

Meeting rooms may have been used repeatedly

Doors/windows may remain closed

and

ventilation conditions may differ.

Compare morning and afternoon historical data rather than relying on one measurement.

Why Does Meeting-Room CO₂ Rise So Quickly?

Meeting rooms often combine:

Small-to-medium room volume

High occupant density

Closed doors

and

Continuous occupancy.

A room containing two people may behave differently when twelve people enter.

This makes meeting rooms one of the clearest applications for occupancy-related CO₂ monitoring.

Why Does CO₂ Drop When I Open the Door?

Opening the door changes airflow between the room and adjacent space.

If the adjacent air has a lower CO₂ concentration, mixing can reduce the room concentration.

The amount and speed of change depend on the actual airflow and concentration difference.

This response can provide useful information—but opening a door is not a complete professional ventilation assessment.

Why Does CO₂ Drop When I Open a Window?

An open window can increase outdoor-air exchange under suitable conditions.

If outdoor CO₂ is lower than indoor CO₂, indoor concentration may decrease as air is exchanged.

But Malaysian users should also consider outdoor conditions such as:

Haze

PM2.5

Traffic pollution

Rain

Heat

and

Humidity.

Reducing CO₂ should not mean ignoring other environmental factors.

Why Does CO₂ Rise Again After I Close the Window?

If occupants remain inside and continue generating CO₂ while outdoor-air exchange decreases, the concentration may begin increasing again.

This creates a useful experiment:

Window closed → observe trend

Window open → observe trend

Window closed again → observe trend

The C1+ historical graph can make these changes easy to compare.

Why Does My CO₂ Reading Jump When I Breathe on the Monitor?

Because exhaled breath contains much more CO₂ than typical indoor air.

This is expected behaviour.

It also demonstrates why you should not test a CO₂ monitor by continuously breathing directly onto it and then interpret that number as room CO₂.

Measure the room, not your breath.

Is 1000 ppm CO₂ “Too High”?

Do not treat 1,000 ppm as a universal safe/dangerous threshold.

Interpretation depends on context, including:

Background CO₂

Occupancy

Room size

Ventilation

Duration

Measurement position

Applicable ventilation requirements

and

the trend.

A single ppm number without context can be misleading.

Is 1500 ppm or 2000 ppm Dangerous?

A consumer CO₂ monitor should not be used to make simplistic medical or regulatory conclusions from one reading.

If you observe persistently elevated CO₂, investigate:

Measurement placement

Occupancy

Ventilation conditions

Possible sources

and

applicable building/workplace requirements.

For professional, regulatory or health-related decisions, obtain appropriate professional guidance.

The C1+ provides measurement data—it does not replace a formal ventilation or occupational-health assessment.

Temtop C1+ Specifications

The Temtop C1+ measures:

CO₂

Temperature

Relative Humidity

CO₂ measurement range:

400–5000 ppm

Specified CO₂ accuracy:

±(40 ppm + 5%) from 400–2500 ppm

The C1+ also supports Bluetooth connectivity and historical data monitoring.

This makes it useful for troubleshooting because users can investigate when the CO₂ changed rather than simply seeing the current number.

Use the Historical Graph Like a Detective

Suppose your C1+ shows an unexpected increase.

Look at the timeline.

Ask:

What time did CO₂ begin increasing?

Then compare that time with:

People entering

Door closing

Window closing

Meeting beginning

Air-conditioning or ventilation changes

Cooking beginning

Exercise class starting

You are looking for relationships.

That is much more useful than staring at the current number.

A Simple Troubleshooting Test

Step 1 — Check Placement

Move the monitor away from direct breathing and strong local airflow.

Step 2 — Establish Background

Observe the room before heavy occupancy.

Step 3 — Record Occupancy

Note how many people enter.

Step 4 — Watch the Trend

Does CO₂ increase gradually?

Step 5 — Change One Variable

Where appropriate, change one ventilation-related condition.

Step 6 — Observe Response

Does the trend change?

Step 7 — Repeat

A repeated pattern is more informative than one isolated event.

Don't Change Five Things at Once

Suppose CO₂ appears high and you simultaneously:

Open the door

Open two windows

Switch on a fan

Change the air conditioner

Move the monitor

The reading may change—but you will not know why.

A better troubleshooting method is:

Change one variable at a time.

Then observe the response.

This is basic measurement discipline.

Is My Temtop C1+ Wrong?

Do not assume instrument failure immediately.

First check:

Placement

Direct breathing

Room occupancy

Doors/windows

HVAC operation

Nearby CO₂ sources

Whether the reading changes logically when conditions change

If readings remain implausible or inconsistent after basic checks, then further instrument verification may be appropriate.

Performance Mode for Troubleshooting

For detailed investigation, the C1+ Performance Mode provides a:

1-minute sampling interval

with approximately:

30 days of specified battery operation.

This is useful when observing changes after:

Opening a door

Opening a window

People entering

People leaving

or

Changing room conditions.

For longer-term monitoring, ECO Mode provides a:

10-minute sampling interval

with approximately:

70 days of specified battery operation.

CO₂ Is Not CO

Another important troubleshooting point:

CO₂ = Carbon dioxide

CO = Carbon monoxide

They are different gases.

The Temtop C1+ should not be used as a carbon-monoxide detector.

If CO is the concern, use an appropriate CO detection instrument.

CO₂ Is Not PM2.5

A room can have elevated CO₂ and low PM2.5.

Another room can have relatively low CO₂ and elevated PM2.5.

Therefore:

CO₂ → occupancy / ventilation-related information

PM2.5 → fine particulate information

During Malaysia's haze periods, understanding both can become important.

Frequently Asked Questions

Why does my indoor CO₂ keep rising?

Occupants continuously generate CO₂. If the room does not dilute it at the same rate through air exchange, concentration can increase.

Why is CO₂ high even with air conditioning?

Cooling does not automatically mean sufficient outdoor-air ventilation.

Why is my bedroom CO₂ higher in the morning?

Several hours of continuous overnight occupancy can create a different CO₂ condition from the beginning of the night.

Why does my CO₂ monitor spike when I sit beside it?

Direct exhaled breath may be influencing the sensor.

Why does CO₂ fall when I open a window?

Outdoor-air exchange may dilute indoor CO₂ if outdoor concentration is lower.

Does an air purifier reduce CO₂?

A typical recirculating particulate air purifier should not be assumed to remove occupant-generated CO₂.

Does high CO₂ mean my air conditioner is faulty?

Not necessarily. Air-conditioning performance and ventilation performance should not automatically be treated as the same thing.

Should I panic when the CO₂ number increases?

No. Check the context, placement and trend. Persistent or concerning conditions can then be investigated appropriately.

High CO₂ Is a Question—Use the Data to Find the Answer

When a CO₂ monitor shows an unexpected number, don't stop at:

“The CO₂ is high.”

Ask:

Why?

When did it start increasing?

Who entered the room?

How long has the room been occupied?

Are the doors and windows closed?

What is the ventilation doing?

Is the monitor correctly positioned?

Is there another CO₂ source?

The Temtop C1+ CO2 Monitor becomes much more useful when treated as an investigation tool rather than simply a number display.

Monitor the trend.

Change one variable.

Observe the response.

Repeat the test.

That is how CO₂ data becomes actionable information.

Contact MTM Precision

MTM Precision Sdn. Bhd.

For Temtop C1+ CO₂ Monitor, indoor CO₂ troubleshooting and ventilation monitoring solutions in Malaysia, contact MTM Precision.

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

Serving customers across Selangor, Kuala Lumpur, Johor, Penang, Perak, Negeri Sembilan, Melaka, Pahang, Kedah, Perlis, Terengganu, Sarawak and Sabah, Malaysia.