Measure Humidity and Find Your Dry Line

• Get a hygrometer
• Salt-test check
• Place it properly
• Seven-day log and your dry line

A common mistake is to change five things at once, see the windows improve or not, and never learn what mattered. Measure first.

§Get a hygrometer

A hygrometer shows relative humidity, often with temperature. Basic digital models are widely sold. Some thermostats show humidity too. If you can, use two: one in the main living area and one in the worst room (often a bedroom).

Relative humidity compares how much vapour is in the air with how much that air could hold at its current temperature. You do not need to calculate with it — watch how it moves and how your windows respond.

§Salt-test check

Cheap units can read a few points high or low. A simple check:

1. Put a few spoonfuls of table salt in a small cup. Add drops of water until you have a damp paste with undissolved salt left.
2. Put the cup and hygrometer in a sealed bag or container. Do not let salt touch the sensor.
3. Leave at steady room temperature, out of sun and away from heaters, for several hours (a full day is steadier).
4. Read without opening. Air over damp table salt settles near about 75% RH at ordinary room temperatures. If yours reads 79, subtract about 4 from future readings and tape the correction on the back.

§Place it properly

• About chest height on an inside wall
• Away from windows, exterior walls, registers, kettles, showers, and sun
• Give it time after you move it — do not trust a one-minute reading

§Seven-day log and your dry line

For one week before big changes, record morning and evening: outdoor temp (rough forecast is fine), indoor temp, RH, window state (dry / edge / lower third / whole), and notes about showers, cooking, laundry, or guests.

On dry mornings, humidity sat below a certain level for that outdoor temperature. On wet mornings it sat above. That level is your home’s dry line, and it moves — colder outside usually means a lower dry line.

Charts from the internet are only a starting point. Your windows are the gauge. Aim to keep humidity just low enough that on the coldest mornings you get only a thin bottom edge of moisture, or none. If that feels too dry for comfort, warm the glass rather than living with wet windows.

Change one thing at a time for two or three days, keep logging, then decide whether it helped.

Originally published at https://dry-glass-notes.surge.sh/articles/hygrometer-dry-line.html (AI-assisted, sources cited). If this helped, zaps go to hollisvarrow3753@coinos.io.