III · Humidity · Seasonal guide · 7 min
What should indoor humidity be in winter?
A seasonal guide to dry air, damp air and the condensation between them.
By Colpo d’Aria Editorial · Published September 24, 2026 · Last reviewed October 1, 2026
The short answer
Aim for roughly 30% to 50% relative humidity. In very cold weather, stay toward the lower end—around 30% to 40%—so moisture does not condense on windows and cold walls.
Why winter changes everything
Cold outdoor air holds little moisture. When it is heated indoors, its relative humidity falls sharply, which is why heated homes often read 15% to 25%. At the same time, cold windows and exterior walls give indoor moisture a place to condense.
Signs the air is too dry
- Static shocks and cracked lips or skin
- Dry, irritated nose and throat, especially on waking
- Gaps in wood floors or furniture joints
- Readings consistently below 30%
Signs the air is too damp
- Water beading on the inside of windows each morning
- Musty odor in closets or corners
- Dark spots on window frames, ceilings or behind furniture
- Readings consistently above 50% to 60%
A guide by outdoor temperature
Many heating professionals reduce the indoor target as it gets colder to protect windows and walls. Treat this as a starting point, not a rule.
| Outdoor temperature | Suggested indoor RH |
|---|---|
| Above 20°F (−7°C) | Up to 40–45% |
| 0°F to 20°F (−18°C to −7°C) | 30–35% |
| Below 0°F (−18°C) | 25–30% |
When condensation calls for ventilation or humidity changes
- Occasional fog after cooking or a shower that clears within an hour: normal; run the exhaust fan longer.
- Daily condensation on most windows: humidity is too high for your windows—lower the humidifier setting and ventilate more.
- Condensation only on one window or wall: suspect a cold spot or air leak; address the surface.
- Mold growth or wet sills: fix the moisture source and increase exhaust ventilation now.
How to adjust
Measure for several days with a hygrometer before changing anything. If air is too dry, reduce excess infiltration first, then add moisture with a clean, well-maintained evaporative humidifier. If it is too damp, exhaust moisture at the source—kitchen, bath, laundry—before reaching for a dehumidifier.