What is the recommended humidity level for a home?
Ideal humidity level for comfort and health is between 40-50%. Lower levels especially in the winter can contribute to a sense of discomfort or chill even at warmer indoor temperatures. Higher levels may result in a clammy damp feeling and foster mold formation.
The humidity level in colder climates can be much lower than 50% in the winter time. The mucous linings of the nose and the shape of your lips can give you an indication that it is too dry. Also, cuticles of your fingers will start to crack if you are in a dry home.
Here is a good guideline based on outside air temperatures.
Outside Temperature Indoor Relative Humidity
Above 50 °F Not over 50%
Above 20 °F Not over 40%
Between 10º & 20ºF Not over 35%
Between 0º & 10ºF Not over 30%
Between -10º & 0ºF Not over 25%
Between -20º & --10ºF Not over 20%
-20ºF or below Not over 15%
If you try to put more moisture into the air, the cold windows will probably start to condense the water back out. You will see water forming a fog on the windows, especially those that face the wind. This is not a good condition since the water will tend to destroy wooden windows and mould can start forming on them. If left for a few days, the water can get into the insulation in the walls and reduce it's effectiveness.