Controls · Sensors
A measured home is a comfortable home.
Sensors are the quiet measurement layer underneath everything in the Controls domain. Temperature, humidity, CO₂ and VOC readings turn vague impressions of stuffiness or chill into something the heating, cooling or ventilation system can actually respond to.
No measurement layer; the house is running on impressions
A house running on impressions; the bedroom feels stale, the bathroom might be damp, and no one has any of the readings that would end the guessing.
What to measure, and why.
Temperature alone is what most thermostats report. It is the least informative of the four. Relative humidity tells you whether condensation and mould are likely; CO₂ tells you whether the air is being refreshed; VOC readings flag furniture, cleaning products or cooking events that the eye misses. Together they describe the comfort of a room far better than degrees do.
A CO₂ reading above 1,200 parts per million in a bedroom overnight is usually a ventilation problem rather than a tiredness one; a humidity reading above 65 per cent in a bathroom sustained through the day is the early warning of a mould problem still weeks away from being visible.
Three sensors: bedroom, bathroom, living area
Same house, three sensors placed where the questions actually live; the bathroom humidity spikes and the bedroom CO₂ trend now describe the ventilation problem in numbers.
Placement, honestly.
A bedroom, a bathroom and a living area is usually enough to understand the building.
Bedroom
- Strength
- Rooms sealed for eight hours at a time; CO₂ becomes the decisive reading for whether ventilation is doing its job.
- Trade-off
- Sensor lights can annoy light sleepers; pick a model with a night-off mode.
- Best for
- Any household where anyone regularly wakes up with a headache or a stuffy feeling.
Bathroom
- Strength
- Humidity spike after showers, and how quickly it recovers, is the single best test of extractor effectiveness.
- Trade-off
- Bathroom electronics need proper IP ratings and thoughtful siting.
- Best for
- Households with black-mould history or a suspicion the extract fan is underpowered.
Living area
- Strength
- One sensor tells you whether the whole-house ventilation strategy is working through the day.
- Trade-off
- Aggregates household activity; harder to attribute events to specific causes.
- Best for
- Baseline reading for any home starting a comfort or air-quality investigation.
Verdict
Sensors, honestly assessed.
Fit three sensors (bedroom, bathroom, living area) for around £90 total, run them for a week, and only then decide whether the ventilation, heating or cooling response needs to change.
For trend purposes, the readings from cheap sensors are trustworthy; absolute calibration drifts a little, but relative change over a week is the useful signal. A five-day trend on humidity and CO₂ typically ends most household ventilation arguments within a fortnight.
Do not put a sensor in every room; three is enough to describe the building. The point of sensors is to feed decisions, not to become the decision.
What it gives you
- Turns vague impressions into readings the system can respond to.
- Cheap; £25 to £45 per sensor for competent PM2.5 / CO₂ / humidity units.
- Makes the case for or against ventilation upgrades measurable rather than argued.
What it costs you
- Absolute accuracy drifts; recalibration is not always practical.
- Data without action is just wallpaper.
- Bathroom units need proper ingress protection.
Why we think thisOpenClose
Reasoning
CO₂ thresholds for bedroom air quality come from CIBSE TM40 and WHO indoor air quality guidance; the 1,200 ppm bedroom overnight figure is the widely-cited threshold at which sleep quality and cognitive performance measurably degrade. Humidity thresholds for mould risk come from BS 5250 and BRE indoor moisture research.
Cost bands reflect UK retail pricing for Aranet, Airthings, Amazon Smart Air Quality Monitor and comparable units in 2026; £25 to £45 for a competent single-parameter sensor, £70 to £180 for a multi-parameter unit that also reads PM2.5.
Assumptions
- Sensors are placed at head height in the space the reading is meant to describe, not on a windowsill or above a radiator.
- The household is willing to act on the readings rather than merely collect them.
- The house is not being deliberately over-ventilated in a way that skews the baseline.
Sources
- CIBSE TM40 Health and wellbeing in building services — CIBSE
- WHO indoor air quality guidelines — World Health Organization
- BS 5250 Management of moisture in buildings — BSI
If this were our house
If this were our house with a suspected damp or ventilation problem and no readings, we would put three sensors in for one week before spending anything else.
- 1Fit a CO₂ + humidity sensor in the worst-affected bedroom at head height, away from a wall and a radiator.
- 2Fit a humidity sensor in the bathroom and record the spike and recovery after each shower for a week.
- 3Fit a baseline sensor in the living area for a whole-house comparison; only after seven days of trend data decide whether ventilation, heating or shading actually needs changing.
A house with active water ingress, penetrating damp or rising damp needs a building surveyor first; sensors describe air, not walls.