Indoor Air Quality Monitoring: Best UK CO2 Guide 2026

Last updated: 13 July 2026

TL;DR: CO2 is the cheapest reliable proxy for ventilation, so indoor air quality monitoring in UK workplaces starts with a CO2 reading in every occupied room. Keep spaces below 800 ppm where you can, investigate anything that sits above 1,000 ppm, and act when readings pass 1,500 ppm. Battery-powered LoRaWAN sensors give every room a live reading for roughly the price of a single wired BMS point, with no cabling and no downtime.

Why is CO2 the best proxy for ventilation?

Occupants are the main source of CO2 indoors, and the gas mixes evenly and quickly, so its concentration tracks the balance between people and fresh air almost in real time. That makes CO2 a cheap, non-intrusive stand-in for measuring ventilation directly, which is slow, disruptive and expensive to do any other way.

Outdoor air holds a fairly stable background level of CO2, while every breath you exhale carries far more. If the fresh air supply keeps pace with the number of people in a room, the reading stays close to that outdoor baseline. If it does not, CO2 climbs within minutes of the room filling up.

The Health and Safety Executive builds its workplace ventilation checks on exactly this logic. Its guidance on using CO2 monitors notes that a reading of 1,000 ppm is equivalent to a fresh air rate of about 10 litres per second per person, and that the Approved Code of Practice expects supply rates of at least 5 to 8 litres per second per person.

Two caveats matter. HSE is clear that CO2 readings are a broad guide to ventilation, not proof of a safe atmosphere. And monitors mislead in rooms with air cleaning units, which remove contaminants but leave CO2 untouched, or where a process itself produces CO2, such as commercial kitchens and plant rooms.

What does UK law say about indoor air quality monitoring?

No UK regulation names indoor air quality monitoring explicitly. Regulation 6 of the Workplace (Health, Safety and Welfare) Regulations 1992 requires you to ventilate every enclosed workplace with a sufficient quantity of fresh or purified air, and continuous CO2 data is the most practical evidence that you actually meet that duty day after day.

HSE’s ventilation in the workplace guidance spells out that employer obligation and treats poor ventilation as a risk you must assess like any other. A one-off assessment tells you about one afternoon. Logged sensor data tells you about every teaching hour, every shift pattern and every season.

Do not confuse ventilation benchmarks with occupational exposure limits. HSE’s EH40 workplace exposure limits set CO2 at 5,000 ppm as an 8-hour average and 15,000 ppm over 15 minutes. Those are health limits for industrial settings, and a typical office should be operating at less than a tenth of them.

Schools have firmer numbers. The Department for Education spent 25 million pounds putting around 300,000 CO2 monitors into state-funded settings, and Building Bulletin 101 sets design and performance standards that CIBSE engineers work to on every school project.

What CO2 thresholds should offices and schools use?

Work to three bands. Below 800 ppm a space is well ventilated. Between 800 and 1,500 ppm ventilation is adequate but worth improving at the top of the range. Consistently above 1,500 ppm means ventilation is poor, and HSE says you should take action. Schools add BB101 daily averages of 1,000 ppm for mechanical systems and 1,500 ppm for natural ventilation.

The DfE guidance for education and childcare settings uses the same colour logic teachers now recognise: under 800 ppm your ventilation is good, 800 to 1,500 ppm is adequate, and over 1,500 ppm you should increase airflow by opening windows and doors. It also recommends non-dispersive infrared (NDIR) monitors and one sensor per classroom.

BB101 goes further for school buildings, as the CIBSE Journal’s analysis of the 2018 revision explains: mechanically ventilated teaching spaces must hold a daily average of 1,000 ppm, naturally ventilated ones 1,500 ppm, and no space should exceed 2,000 ppm for more than 20 consecutive minutes in a day.

How much does stuffy air cost in performance?

More than most facilities budgets admit. In Harvard’s controlled double-blind study, cognitive test scores fell 15 percent when CO2 was raised to around 945 ppm and 50 percent at around 1,400 ppm, both well inside the range UK meeting rooms reach by mid-afternoon. Ventilation quality moved measured thinking ability, not just comfort.

The full study, published in Environmental Health Perspectives, found that a 400 ppm increase in CO2 was associated with a 21 percent decrease in cognitive scores across all test domains, and that scores were 61 percent higher in green building conditions and 101 percent higher with enhanced ventilation, compared with a conventional office.

The stakes go beyond productivity. The World Health Organization attributes around 7 million premature deaths a year to the combined effects of ambient and household air pollution, which is why its guideline values now also shape how landlords and employers think about the air inside their buildings.

What should you measure beyond CO2?

Four things cover almost every workplace complaint: CO2 for ventilation, PM2.5 for fine particles, TVOC for chemical off-gassing, and temperature with relative humidity for comfort and mould risk. A single multi-parameter sensor captures all of them, so the marginal cost of measuring properly rather than partially is small.

PM2.5 deserves particular attention because the health evidence keeps tightening. The 2021 WHO air quality guidelines halved the recommended annual mean for PM2.5 from 10 to 5 micrograms per cubic metre and cut the 24-hour value from 25 to 15. Indoor sources include printers, cooking, construction dust and traffic ingress through windows and intakes.

TVOC picks up cleaning chemicals, new furniture and flooring adhesives, the classic culprits behind headaches in refurbished offices. Temperature and humidity round out the picture: persistent RH above 70 percent flags condensation and mould risk, while dry winter air below 40 percent drives complaints about eyes and throats.

On hardware, a Milesight AM103 covers CO2, temperature and humidity for straightforward classroom and office monitoring. The AM307 and AM308 add TVOC, light and occupancy sensing, with the AM308 including PM2.5 and PM10. For washrooms, the GS301 tracks ammonia and hydrogen sulphide instead.

How do LoRaWAN air quality sensors compare with a BMS retrofit?

A LoRaWAN sensor is battery powered and wireless, so it goes on the wall in minutes with no cabling, no ceiling work and no electrician. One gateway typically covers a whole building. A wired BMS retrofit needs new sensor points, containment, controls integration and commissioning, which is why per-room monitoring rarely survives the budget meeting.

The arithmetic is blunt. At the time of writing, an AM103 costs 142.15 pounds and the EM500-CO2, a 4-in-1 sensor built for harsher spaces such as kitchens and plant rooms, costs 179.56 pounds on our store. The multi-parameter AM308 is 291.79 pounds. Batteries last years, and readings arrive every few minutes over a network you own.

Because LoRaWAN signals travel hundreds of metres indoors and penetrate floors and walls, a 20-classroom school or a mid-size office usually needs exactly one gateway. There is no monthly SIM per sensor, and adding a room later is a five-minute job rather than a variation order.

The trade-off is direction: LoRaWAN monitoring tells your team when and where to act, but it does not drive dampers and fans itself. If you already run a capable BMS, sensor data can still feed it. If you do not, monitoring plus manual or scheduled ventilation changes captures most of the benefit at a fraction of the cost.

How do you deploy indoor air quality monitoring and when does it pay back?

Start with one sensor per regularly occupied room, mounted at seated head height, at least 50 cm from the nearest person and away from windows, doors and supply vents, following HSE and DfE placement advice. Stream readings to a dashboard with alerts at 1,000 and 1,500 ppm, then review a full occupied week before changing anything.

The first payback is time. Instead of investigating vague complaints about stuffy meeting rooms, your team opens a dashboard and sees which rooms breach 1,500 ppm, at what time, and how fast they recover. Ventilation spend then goes only where the data says it must, rather than across the whole estate.

The second payback is energy. Rooms that never approach 800 ppm are being over-ventilated, and every litre of that surplus air is heated in winter. Trimming it is one of the quickest wins to surface, and pairing air quality data with energy monitoring shows exactly what each adjustment saves.

The third is evidence. Logged CO2 history answers tenant disputes, school governor questions and HSE inspections with data rather than assurances. Our smart buildings solution page shows how the sensors, gateway and dashboard fit together in a typical deployment.

Frequently asked questions

What is a good CO2 level in an office or classroom?

Below 800 ppm indicates good ventilation, according to both HSE and DfE guidance. Between 800 and 1,500 ppm is adequate, and consistent readings above 1,500 ppm mean ventilation is poor and needs action. For schools, BB101 sets daily averages of 1,000 ppm for mechanical ventilation and 1,500 ppm for natural ventilation.

Is indoor air quality monitoring a legal requirement in the UK?

Not by name. But Regulation 6 of the Workplace (Health, Safety and Welfare) Regulations 1992 obliges employers to supply sufficient fresh or purified air in every enclosed workplace, and HSE guidance points to CO2 monitors as the practical way to check. Continuous indoor air quality monitoring is how you evidence compliance, not the duty itself.

Where should CO2 monitors be placed in a room?

At seated head height, at least 50 cm away from people so exhaled breath does not skew readings, and away from windows, doors and air supply openings. In larger spaces, use several monitors. HSE also advises taking frequent readings across the occupied day and working from the average, not single peaks.

How many air quality sensors does a building need?

DfE guidance treats one sensor per classroom as sufficient, and the same logic works for offices: one per meeting room and one per open-plan zone. Prioritise densely occupied, poorly ventilated spaces first. Because LoRaWAN devices are wireless and battery powered, you can start with ten rooms and scale later without rewiring.

Do CO2 sensors need recalibrating?

Occasionally, yes. DfE guidance recommends NDIR sensors and periodic calibration in line with the manufacturer’s instructions. Most modern NDIR devices, including the Milesight units we stock, support automatic baseline calibration that re-zeroes against fresh outdoor air, so routine maintenance is usually limited to battery changes every few years.

Where do you start?

Pick your five worst rooms, fit a CO2 or multi-parameter sensor in each, and let two weeks of data make the case for the rest of the estate. Browse our air quality sensors or request a quote and we will spec the full indoor air quality monitoring stack, sensors, gateway and dashboard, for your building.