Carbon Dioxide Monitoring

Find out how well ventilated your home is

Why borrow a CO2 monitor?

CO2 monitors display and record carbon dioxide levels (CO2), temperature and relative humidity (% RH). We breath out CO2 and humidity all of the time, and lots household activities produce moisture too, like showering, cooking and drying clothes.  But too much or too little CO2 or humidity usually indicate poor ventilation, which may cause a range of problems problems. For example:

  • Excess CO2 can cause drowsiness and discomfort, making it harder to concentrate
  • Excess humidity can cause condensation and mould growth, damaging our homes and exacerbating respiratory conditions and allergies
  • Low levels of CO2 and humidity may indicate a house is losing more air than needed, requiring more energy to heat the home

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

It’s possible to reduce draughts and control ventilation with window trickle vents, by opening windows and running extractor fans, as needed. If you have one, you can also use a ventilation system like an MVHR.

CO2 monitor loan scheme

CCF has two CO2 monitors available on free loan with booking online.  The availability of each monitor is shown in the booking calendars.
See the resources below for useful information.   CO2 Monitor loans are free, but donations to Cambridge Carbon Footprint are welcome. 

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.

CO2 readings in a bedroom over 2 nights

What are the safe levels of CO2?

Envisense guidance on CO2 levels in the home

* This rising CO2 level 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 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

Indoor CO2 levels and COVID-19 transmission risk

Raised CO2 levels can also indicate a higher risk of COVID-19 transmission as a result of poor ventilation. More people in a smaller space that has poor ventilation, especially if they’re active and breathing hard, all increase the risk.

UK Government has sent 300,000 CO2 Monitors to all schools to monitor for this risk.

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, if you have a home appliance or fire burning gas, wood, etc, especially without a flue.