Carbon Dioxide Monitoring

Find out how well ventilated your home is

Why borrow a CO2 monitor?

These CO2 monitors display and record carbon dioxide levels in ppm (parts per million).
We breath out CO2 and if it accumulates in a room due to poor ventilation, that can cause drowsiness and discomfort, making it harder to concentrate.
High CO2 levels also indicate an increased risk of airborne infection between people in the room, as used in schools, etc during Covid.

Most people aren’t good at noticing when the air is stuffy, so CO2 monitors are a useful tool  to see how well ventilated our homes are and take action if needed.

In winter low levels of CO2 may indicate a house is losing more air than needed, wasting heat.   You can have too much ventilation as well as too little!  


These monitors also display and record Temperature and Relative Humidity (%RH). 
Humidity meters are low-cost and you may want to buy one to use long-term.
High humidity, eg: >70%, may cause condensation on cold surfaces, which can lead to mould or rotting timber, damaging our homes and exacerbating respiratory conditions and allergies.  

It’s usually caused by household activities, like showering, cooking and drying clothes indoors.  Excess humidity can usually be controlled by putting less moisture into the house, using extractor fans in the kitchen and bathroom and good general ventilation with window trickle vents and opening windows, as needed. 
If high humidity, dampness or mould persist, you may have water leaking into the house from missing roof tiles, blocked gutters, etc. 

Book a CO2 Monitor Loan

We have 3 CO2 monitors available to borrow by anyone. Cameras are hosted by volunteers in Cambridge City, Histon and Great Cambourne.


Bookings will available from 15th December ’23 to 12th April ’24.

How to use a CO2 monitor

We recommend using one to check the ventilation during normal use, in rooms where you spend most time – probably living rooms and overnight in bedrooms. Maybe check how long it takes for the bathroom to return to good humidity (ideally 60% RH or less) after a shower.

The logging function is good for overnight tests, recording hourly measurements. Then connect the monitor to a computer via USB; it appears as a disk drive, containing a CSV file of recent readings. 

If indoor CO2 remains less than 800ppm and it’s cold outside, you may be wasting heat from draughts or too much ventilation.

What are the safe levels of CO2?

Envisense guidance on CO2 levels in the home

* This rising CO2 level, now 420ppm, is the main cause of climate change. 

UK Health and Safety Executive guidance 

5,000 ppm** CO2 as the long-term (8-hr) workplace exposure limit.
HSE Guidance on using CO2 Monitors  advises actions for these CO2 levels:

1500ppm   Take action to improve ventilation where CO2 readings are consistently higher than 1500ppm

800ppm or less is likely to indicate that a space is well ventilated.
Where there is continuous talking or singing, or high levels of physical activity, provide ventilation sufficient to keep CO2 levels below 800ppm

**ppm = parts per million

CO Alarm

Don’t confuse this Carbon Dioxide (CO2) Monitor with Carbon Monoxide (CO) Alarms. Carbon Monoxide is the seriously poisonous gas made by incomplete combustion. It’s good to have one to warn you of dangerous CO levels in any room where you have a home appliance or fire burning gas, wood, etc, especially without a flue.