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CO2 Meters

Air quality is taonga and is essential to human health and wellbeing. While outdoor air quality will always influence indoor air quality levels, the vast amount of our daily over-exposure to carbon dioxide (CO2) unwittingly occurs in poorly ventilated indoor environments.

The good news is that from Thursday 9 March you can borrow CO2 meters from the library to help you monitor your indoor air quality levels. Have a read below to find out more about this service.

How does the service work?

  • You can borrow one CO2 meter at a time for 10 days
  • CO2 meters can't be renewed
  • CO2 meters can be picked up in person or reserved online through the catalogue. To reserve, choose your preferred branch and when it's ready to collect, pick it up from a librarian at the library desk
  • Please return your CO2 monitor directly to a librarian to avoid damage in the returns chute

How much does it cost?

  • CO2 meters are free to borrow
  • For lost or damaged items, a replacement cost is charged:
    • $457 for Aranet4
    • $109 for Air Detector, plus $15 for USB charger cord and $15 for USB plug

Where can I find them?

We currently have six CO2 meters across the city, available from the following branches:

Find a CO2 meter on our catalogue

Why CO2 meters?

A CO2 monitor can help you:

  • Measure your indoor CO2 concentration, temperature and relative humidity levels
  • Obtain readings from around your home, office or classroom, under different usage levels and conditions, to determine ways to improve your air quality in the spaces you frequent the most.

The CO2 meters are easy to use and provide instant readings, to help you have more awareness around how healthy your indoor air is and where improvements might be needed.

Read our CO2 Monitor In-Depth FAQs for more information about why we offer these items

Important usage notes

  • The CO2 meters are for domestic home and office use only and are not suitable for use in industrial or commercial environments.
  • The CO2 meter should ideally be placed clear of any obstacles surrounding its sides, and approximately 2 meters away from windows, inhabitants, or open flames (ideally on a stable tabletop). Do not expose to extreme heat, cold, moisture or dust.
  • CO2 meters cannot indicate of the presence of COVID-19.

Have feedback about this service? CO2 Meter Survey

Have you used this service? Have feedback? We'd love to hear your experience – use the form below to get in touch:

Co2 Meter Survey — Feedback Form

In-depth FAQs — CO2 Meters

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Why is monitoring indoor air quality important?

Air quality is essential to human health and wellbeing. A person inhales around 14,000 litres of air a day, and the pollutants in the air can adversely affect not only our health, but the health of our environment.

Air quality is contaminated by a complex mixture of human made and natural sources that result in particulate matter and gaseous pollutants entering the body via breathing. The vast amount of our daily over-exposure to carbon dioxide (CO2) unwittingly occurs in poorly ventilated indoor environments.

What is CO2 and why is it a concern?

Carbon dioxide (CO2) is a gas consisting of one part carbon and two parts oxygen. It is a ubiquitous compound found in the air, formed by combustion processes, human exhalation, and a variety of other natural and man-made processes. CO2 is an odourless, colourless, and tasteless gas, and while it is harmless in small quantities too much exposure can result in negative health effects.

Increased levels of CO2 are directly correlated to low productivity and high sick leave in schools, offices, and home environments . CO2 is measured in parts per million (ppm) and can be used as an indicator of a room's ventilation requirements, as the main source of high CO2 levels indoors is occupants . When combined with a lack of airflow and everyday activities like gatherings, gas top cooking, home heating, and using a clothes dryer, significant and unhealthy accumulation of CO2 can occur.

Recommended safe levels and impacts

Standards New Zealand Te Mana Tautikanga o Aotearoa set safe indoor CO2 levels at below 1000ppm:

  • Tolerable exposure (1,000-1,400ppm) can cause a lack of focus, tiredness, impaired judgement and decision-making ability and fatigue
  • Higher exposure (above 1,400ppm) can cause increased heart rate, headaches, dizziness, nausea and cognitive dysfunction
  • Significant long-term health effects are not generally expected below 5000ppm

These health impacts also adversely affect vulnerable populations such as young, elderly, and people with pre-existing respiratory conditions.

Relative humidity and temperature measures

The CO2 meter also provides readings for relative humidity (measured in percentage %) and temperature (measured in degrees Celsius °C or Fahrenheit °F). Maintaining healthy indoor temperature and humidity levels is vital to our health and the integrity of our bodies and homes.

Cold, damp houses pose health risks in many ways and are a common housing problem across New Zealand. The World Health Organisation (WHO) recommends a minimum indoor temperature of 18°C, or 20°C for houses with elderly, ill people, or young children. Indoor temperatures below 16°C increase the risk of respiratory infections, and temperatures below 12°C put stress on the cardiovascular system .

Relative humidity is a measure of the amount of water vapour in the air in relation to the maximum amount of water vapour (moisture). When the temperature rises, the air can hold more water vapour, colder air cannot hold as much moisture. Humidity is a natural part of our atmosphere, and everyday activities such as washing dishes, showering, and breathing also can affect humidity levels.

  • Healthy indoor relative humidity levels are between 40%-60%
  • Lower humidity levels (below 40%) may mean the air becomes too dry and uncomfortable, exacerbating allergic skin conditions, causing dry eyes and irritated respiratory passages
  • Higher indoor humidity levels (above 60%) provide an excellent home for the growth of unwanted mould, bacteria, and dust mites, which also severely exacerbate allergies and other respiratory conditions such as asthma
  • Damp and mouldy conditions indoors increase the risk of bronchitis, respiratory tract infections, mould sensitisation, and respiratory toxin production

How do I read the numbers on the screen?


Carbon Dioxide (CO2) in parts per million (ppm)
Level Health effect Action
Good indoor air quality (displays green) Below 1000ppm Maintains your healthy levels. Use intermittent ventilation when reaching approximately 800ppm and higher.
Tolerable indoor air quality (displays yellow/orange) 1000 – 1400ppm Mild health effects, brain cognitive function decreases by 15%. Routinely ventilate, consider reducing capacity, or altering room usage.
Unhealthy indoor air quality (displays red) More than 1400ppm Moderate short term health effects, brain cognitive function decreases by 50%. Immediately and consistently ventilate, and/or run air filtration system.
  • Significant long-term health effects are not generally expected below 5000ppm.
  • The green, yellow/orange, red coloured bars/quadrants on the meter correlate to the ppm reading
  • When the Air Detector meter reads over 1000ppm it will alert with audio (loud beep) and visual (flashing screen) alarms to indicate that ventilation is required


Temperature (Degrees Celsius °C)
Range Risk
Good indoor air quality 18 - 24°C Safe, ideal range for general population
Tolerable indoor air quality 16 - 18°C and 25 - 30°C Minimal-risk indoor ranges for general population. May negatively affect vulnerable populations such as young children, elderly, and people with pre-existing respiratory conditions
Unhealthy indoor air quality Below 16°C Minimum recommended indoor range. Increased negative health risks for general population.

Both models can display the temperature in both °C or °F — the default setting is °C. To change this setting:

  • On the Air Detector — click the power button once (when the model is already turned on) to change the temperature reading from degrees Celsius (°C) to Fahrenheit (°F).
  • On the Aranet4 — the temperature setting is located underneath the batteries (see User Manual)

Relative Humidity

Relative Humidity - percentage (%)
Range Risk
Good indoor air quality 40-60% Ideal indoor relative humidity.
Tolerable indoor air quality 30% - 40% and 60% - 70% Tolerable indoor relative humidity, may affect people with allergies.
Unhealthy indoor air quality Below 30% Dry skin, itchy eyes, nasal passage and throat irritation, increased allergy symptoms, increased vulnerability to infection, dehydration
Above 70% Mould, dustmite & bacterial breeding increases, respiratory disease risks increase, increased allergy symptoms, dehydration

Battery life and charging our meters

Each model comes with a USB cord and wall adaptor for charging.

Air Detector

  • The fully charged battery will last approximately 6-8 hours if it is in continual use.
  • This model has an on/off button and can be used whilst it is plugged in charging if necessary.
  • The battery should be fully charged when you pick it up


  • The Aranet4 has a power efficient 'E-ink' screen with a long battery life.
  • There is no on/off button.

Please note: Even when the AA batteries are removed, the screen will still visually appear with the last recorded reading on it. This means that you need to check if the batteries are still installed when you return the device or check if the screen is refreshing its reading (occurs approximately every 2-3 mins).

Please check the battery icon on the home screen and replace with new AA batteries if flat or missing. Please responsibly recycle the old batteries.

Why do you offer two different models?

We are testing two different models of CO2 meters for a trial period and following customer feedback we will be evaluating the usage and accuracy of each model.

The CO2 Meter Information Pamphlet contains information relevant to both models. The user guides differ slightly, however both models are self-explanatory and simple to operate with the aid of the information pamphlet.

Is the CO2 Meter for household use only?

Yes, both models are only suitable for indoor, home use. Similar environments, such as a moderately sized office, or classroom would also be suitable locations.

The CO2 Meters are not for commercial or industrial use, and do not have the capability to perform accurate readings within these settings.

CO2 Meters should not be used in environments with excessive dust, moisture or temperature extremes. The operating temperature range is 0°C to ~45°C. Avoid exposure to rain and strong sunlight. Strong magnetic fields should also be avoided. Exposing the device to extreme conditions will inhibit (and potentially destroy) the CO2 Meters internal sensors, battery, and air inlets.

Where is the best location in the home to place the CO2 Meter?

Place the CO2 Meter on a stable surface (preferably a table or similar), approximately 2 meters away from windows, occupants, and heat sources. The Aranet4 can also hang on a wall hook/nail. The screen will display readings automatically once powered on/installed with batteries.

Can I connect to the Aranet4 with my smartphone?

The Aranet4 has smartphone capabilities, and can be connected via Bluetooth to an app, to provide remote updates on CO2 readings over time. For more details see the User Manual (requires downloading of a free app).

The Air Detector model does not have smartphone capabilities.

Does the CO2 Meter indicate for COVID-19?

No. Recently CO2 readings have been used as an indicator of the risk levels of airborne infection transmission and can be used as a precautionary measure for the community to ensure adequate fresh air is circulating in indoor spaces.

Please note that CO2 meters are not an indicator of the presence or absence of COVID-19, but are a useful tool to gauge how well-ventilated an occupied indoor space is.

Further Reading

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