Last Updated on October 25, 2026 by Umar Farooq
How to log humidity at home: put one hygrometer in the room you are worried about, record relative humidity and temperature at least four times a day for seven days, and write down what was happening each time (shower, cooking, laundry, windows). A logging sensor does the writing for you; a notebook does it for free.
A single reading tells you what the air is doing this minute, which is about as useful as judging a diet by one weigh-in. The pattern across a week is the part that tells you whether you have a ventilation habit, a damp room or a building fault.
Pick the logger you will actually look at
Two options, and neither needs to be clever.
- A logging hygrometer or a smart sensor with history. It stores readings itself, usually every few minutes to an hour, and shows you a graph. The advantage is the 3 a.m. readings you would never take by hand. This is where the overnight rise shows up.
- A plain hygrometer and a notebook. Fine, if you read it at fixed times and write the number down straight away. The risk is gaps: miss the shower spike and you miss the evidence.
I am not going to name a model. Any sensor that records temperature and relative humidity, and keeps its history, does this job, and how accurate hygrometers really are matters less than you might fear, because you are reading a trend, not a decimal. The EPA’s brief guide describes a humidity meter as an inexpensive instrument sold at many hardware stores. That is all you need.
If you are still choosing a spot, where to put a hygrometer covers placement properly. The one rule that matters here: once it is in position, do not move it for the week, or you are comparing two different rooms and calling it a trend.
How to log humidity at home with or without a logger
Whichever you use, the routine is the same.
- Let it settle for an hour, then start. A sensor carried in from a cold car is not telling the truth yet.
- Leave it in one spot for seven days. Seven is my judgement, not a standard: it gets you through a weekend, when routines differ, and through at least one wash day.
- Log the same fields every time. The ones below are all you need.
- Include the dull days. A week where you ran the extractor fan and aired the room religiously will tell you what your best case looks like. That is also useful.
If you have no logger, read at fixed times: when you get up, around midday, early evening and just before bed, plus once after anything obviously steamy.
| Field | Why it earns its place |
|---|---|
| Date and time | Lets you match a peak to a routine |
| Room | A logger in the bedroom says nothing about the kitchen |
| Relative humidity (RH, %) | The headline number |
| Temperature (°C / °F) | The same moisture reads very differently at 12 °C and 21 °C |
| What happened | Shower, cooking, drying washing, window open, heating on, people home |
That last column is the one people skip, and it is the one that turns a graph into an answer. A spike with nothing written next to it is a mystery. A spike labelled “shower, door shut” is a diagnosis. If you are curious why temperature belongs in the log, how humidity is measured explains why RH moves when the temperature does.
Read the shape before you read the number
When the week is up, look at the graph (or your notebook column) for four shapes. The diagram above shows all four on a made-up day, so treat it as a legend, not as a result.
Daily peaks. A sharp spike after a shower or cooking that falls back within a few hours is normal. Moisture went in and ventilation took it out. This is not a problem, and a lot of people buy a dehumidifier to cure it when a longer fan run would do.
An overnight rise. If humidity creeps up through the night in a closed bedroom and drops once the door and window open, the source is breathing and no ventilation. Your decision is about airflow, not equipment.
A persistent high in one room. If one room sits above the rest all day and every day, something is feeding it or it is cold. Compare it with your other readings before you decide which.
A high daytime floor. This is the one I watch. If the lowest point of the day never gets below about 60%, the spikes hardly matter, because the house never dries out between them. The EPA says to keep indoor humidity below 60 percent, ideally 30 to 50 percent, and a persistent baseline above that line is what a logger is best at catching. For what those targets mean room by room, see what indoor humidity should be.
Humidity problem or building problem?
This is the question a log can help with, and it is worth being clear about where it stops.
A cold-wall reading is the clearest case. If you put a second sensor against a cold external wall and it reads far higher than the room, the wall surface is cold enough to wet itself. That points to condensation and insulation, not to the air being too damp overall.
A building-conservation guide makes the same distinction in a bigger setting: a general moisture level suggests high humidity throughout the building, while localised high readings are more likely linked to a building defect. Their example is a timber end set into a damp wall, but the logic carries over to a house. One wet spot while the rest of the room is dry looks like a leak, a bridged damp-proof course or a failed seal, not a ventilation habit.
A logger cannot prove a leak. It can only tell you that the pattern does not look like ordinary household moisture. Confirm with a visual check and, if needed, a damp meter or a surveyor.
My rule of thumb, which is judgement rather than a published threshold: if the whole room’s baseline is high and falls when you ventilate, treat it as humidity. If one spot stays wet whatever you do, go and look for water.
What each pattern tells you to do
| What the log shows | Likely meaning | Sensible next step |
|---|---|---|
| Spikes that fall within hours | Normal activity | Run the fan longer; open a window after |
| Overnight climb in a shut bedroom | Moisture from sleeping, little air change | Trickle vent or crack a window |
| High all day in every room | Whole-house moisture | Ventilate more; consider a dehumidifier |
| One room high, others fine | Local source or cold surfaces | Find the source; check the cold wall |
| Always wet in one spot, ventilation changes nothing | Possible leak | Inspect for water ingress |
Use the log to ventilate at the right times. If outdoor air is drier than indoor air, a window is the cheapest dehumidifier going; the log shows you which hours that works. If the baseline stays high after you have ventilated properly, that is when a dehumidifier earns its place, and the log is the evidence for it. Keep logging after you change something: the second week’s graph is the only honest test of whether it worked.
It also helps with houses you are not in. A logger left running in a vacant property shows damp building up while you are away, which is why how to stop damp in an empty house recommends one.
FAQ
How long should I log humidity for?
Seven days is a good minimum for a first look, because it covers a weekend and a laundry day. I chose that number myself rather than quoting a standard. If readings sit near the 60% line, keep going for a second week or a different season.
How often should I record humidity readings?
A logging sensor every 10 to 60 minutes is plenty. By hand, four fixed times a day plus one after steamy activities will show the main peaks, though you will miss the overnight detail.
What should I write down besides the humidity percentage?
Temperature, room, time and what was happening: showers, cooking, drying clothes, windows open, heating on. The event notes are what let you match a peak to a cause.
Do I need a smart sensor or an app to log humidity?
No. A smart sensor saves effort and records overnight, but a basic hygrometer and a notebook produce a usable log if you are consistent about the times.
Can a humidity log tell me if I have a leak?
Not on its own. A log can show that one spot behaves differently from the rest of the room, which is worth investigating, but a leak needs a visual check or a damp meter to confirm.
Is a spike after a shower a problem?
Not if it falls back within a few hours. The worry is a baseline that never comes down between spikes.
