HCHO (Formaldehyde) Readings Are Low or Zero

It's completely normal for HCHO (Formaldehyde) readings to remain very low or even display 0.000 mg/m³ for extended periods.

Unlike pollutants such as PM2.5 or CO₂, formaldehyde is not continuously present in most indoor environments. If no measurable formaldehyde is detected, Airmonitor Plus will simply display a very low or zero reading.

In most cases, this indicates good indoor air quality, not a fault with the monitor.

What Is Formaldehyde?

Formaldehyde (HCHO) is a colourless gas that can be released from a variety of household products and building materials.

Common sources include:

• New furniture
• Composite wood products
• Flooring
• Paints and varnishes
• Adhesives
• Building materials
• Some fabrics and textiles

Levels are often highest in newly built, recently renovated or newly furnished homes.

Why Is My Reading Always Zero?

Many homes have extremely low formaldehyde concentrations.

If no measurable formaldehyde is present, Airmonitor Plus will correctly display a reading close to 0.000 mg/m³.

This is generally a positive sign and indicates that your indoor air contains very little formaldehyde.

How Can I Check the Sensor Is Working?

If you'd like to confirm that the HCHO sensor is responding, move Airmonitor Plus into an environment where formaldehyde levels may be temporarily higher.

For example:

• A recently painted room.
• A room containing new furniture.
• An area where strong adhesives or solvents have recently been used.

Allow several minutes for the sensor to respond after moving the monitor.

Important: Do not deliberately expose Airmonitor Plus to concentrated chemicals or hazardous fumes, as this may damage the sensors or create an unsafe environment.

Can HCHO and TVOC Increase Together?

Yes.

Many products that release volatile organic compounds (TVOCs) may also release small amounts of formaldehyde.

For this reason, it's common to see both readings increase after:

• Decorating.
• Bringing new furniture into a room.
• Using certain cleaning products.
• Renovation work.

Frequently Asked Questions

Is a zero reading normal?

Yes. In many homes, formaldehyde levels are extremely low, so a reading close to zero is completely normal and usually indicates clean indoor air.

Does a zero reading mean the sensor isn't working?

No. A low or zero reading simply means that no measurable formaldehyde has been detected. It does not indicate a fault with the sensor.

How quickly does the sensor respond?

The HCHO sensor continuously monitors the surrounding air. If formaldehyde levels change, the reading will gradually update as fresh air passes through the monitor.

My TVOC reading changes but HCHO stays at zero. Is that normal?

Yes. TVOCs represent a wide range of gases, whereas HCHO measures only formaldehyde. Many everyday products release VOCs without releasing measurable amounts of formaldehyde, so it's normal for the two readings to behave differently.

When should I contact Breathe Tech Support?

If your HCHO reading never changes, even after several weeks of normal use and in environments where formaldehyde is likely to be present, please contact Breathe Tech Support. We'll be happy to help you check that your monitor is operating correctly.