What should relative humidity be at or less than in winter?

Maintaining relative humidity at or below 40% during winter is important for several reasons. As temperatures drop, the capacity of air to hold moisture decreases. If the humidity level rises above 40%, it can contribute to condensation on windows and walls, which can lead to moisture-related issues such as mold growth and damage to building materials.

Furthermore, maintaining a relative humidity level around or below 40% helps to improve indoor air quality and comfort. High humidity levels can make the air feel colder than it is, increasing the need for heating and making energy consumption more costly. Conversely, low humidity levels help to prevent the discomfort associated with overly moist air, such as sticky conditions and temperature unevenness.

This recommended humidity range also aligns well with the comfort levels of occupants, helping to create a healthy indoor environment while minimizing potential damage to both the structure and furnishings of a home. Thus, keeping relative humidity at or below 40% is considered best practice during the winter months.