CO2 Meters | Air Quality Monitors | Carbon Dioxide Detectors

We sell a narrow range and we would rather you bought the right thing once. This is the short version of what a carbon dioxide reading tells you, what it does not, and how to pick between the two monitors.

What a CO2 monitor actually measures

Carbon dioxide in parts per million, plus temperature and humidity. Indoors, CO2 is mostly a headcount problem: people breathe it out all day, so when fresh air stops replacing the air in a room the level climbs. That makes it the simplest stand in for ventilation, which is otherwise invisible.

Reading the number

Outdoor air sits around 400 to 420 ppm, so that is the floor and no indoor room reads below it. A room with air genuinely moving through it usually stays under 800 ppm. Once a reading sits above roughly 1000 to 1500 ppm, the room is largely recycling the air already in it.

Those are ventilation benchmarks and not health limits. A high reading means the room needs more fresh air. It does not mean anything harmful has been detected, and a CO2 monitor is not a safety device.

The two minute test worth doing first

Note the reading, open a window, and watch what happens. Some rooms drop hundreds of ppm in a couple of minutes, which means ventilation is fine and the room just needed it. Others barely move, which tells you the airflow is not where you assumed. That single test is worth more than any absolute number, because it tells you whether the fix you were planning will work in that room.

Which of the two monitors

The measurements are identical, so it comes down to who needs to read it. The compact CO2 meter is palm sized at 108 g, reads 400 to 5000 ppm, refreshes every second and has an audible alarm, which suits one person checking several rooms or watching a bedroom or a desk.

The jumbo monitor is the wall mounted version with a large format screen. Buy that where a room full of people needs to see the number, because a reading on a wall gets acted on by whoever is nearest the window and a reading on a desk gets checked once a week.

How many you need

Count separately ventilated rooms rather than floor area. A room with its own door, windows and vents behaves differently from the one beside it, so one monitor describes its own space and little else. Two rooms sharing one open plan airflow can share a monitor; two closed rooms cannot.

Where to put it

Head height, away from a window and away from a doorway, and not where someone breathes directly onto it. A monitor on a windowsill measures the incoming air, reads reassuringly low, and tells you nothing about the room.

What these will not do

They do not detect carbon monoxide, which is a different gas needing its own alarm, and if you have any fuel burning appliance you should fit one regardless. They do not measure particulates such as PM2.5, or volatile organic compounds. Neither publishes an accuracy tolerance, so we do not quote one, and no calibration certificates are available.

Our ozone machines are also not air purifiers in the filter sense. Ozone is a respiratory irritant, so a space is treated while empty and aired out before it is used again.

Questions before you order

If you are not sure which monitor suits your room, or whether we sell the right instrument for your problem at all, ask first. If what you actually need is a particulate or VOC meter we will tell you, because that is cheaper for both of us than a return.