Understanding indoor humidity

Humidity is one of the few indoor air readings you can actually feel: a damp room feels clammy, and a dry one feels crisp and slightly harsh. But "feeling humid" and knowing the actual number are different things, and the number is what tells you whether it's worth doing anything about it.

What the percentage actually means

Indoor humidity is usually shown as relative humidity (%RH) — how much moisture the air is holding compared to the maximum it could hold at that temperature. It's relative because warm air can hold more moisture than cold air, which is why the same amount of moisture can feel humid in a warm room and less so once that room cools down.

For most homes, a comfortable range sits roughly between 30% and 60% RH. Below that, the air starts to feel dry. Above it, the air feels damp and close, and mould and dust mites can thrive more easily.

What actually moves the number

• Cooking and showering release a large amount of moisture into the air very quickly.
• Drying laundry indoors is one of the most common causes of persistently high humidity in a home.
• The weather and season set a baseline — humid summer air outside pushes indoor humidity up too, while cold winter air holds very little moisture, which is part of why heated homes often run dry in winter.
• Ventilation is the main lever you have. Extractor fans, opening a window after a shower, and simply airing a room out all move humidity back toward a comfortable range.
• Number of occupants and pets — more bodies breathing and moving through a space adds moisture over time, particularly in smaller rooms.

Bringing humidity back into range

If it's running high

• Run the extractor fan during and after cooking or showering, and leave it on for a few minutes afterwards
• Avoid drying laundry indoors where possible, or ventilate well if you must
• Consider a dehumidifier for consistently damp rooms, particularly bedrooms and bathrooms with limited ventilation
• Wipe down condensation on windows rather than letting it sit

If it's running low

• A humidifier can help in small, frequently heated rooms during winter
• Houseplants make a marginal difference at best; they're not a substitute for a humidifier if the air is genuinely dry
• Reducing heating slightly, where comfortable, can help, since warmer air holding the same moisture reads as lower relative humidity

Why it's worth tracking, not just guessing

Because comfortable humidity is a range rather than a single target, the useful habit isn't checking it once — it's noticing the pattern. A bathroom that regularly climbs above 70% after a shower and takes an hour to recover tells you the extractor fan needs a longer run time, or isn't powerful enough. A bedroom that sits consistently below 30% in winter tells you a small humidifier might be worth trying. The Atmosense Core CO₂ shows humidity alongside temperature and CO₂, and the app keeps a history, so you can see how it moves through the day rather than relying on a single damp morning or a static-shock evening to notice something's off.