Indoor humidity in winter is a greatly neglected and often little-known part of airconditioning; yet its importance cannot be underestimated, for, at least to some degree, health and comfort depend upon it.
In summer we have learned to cool and dehumidify the air; in winter we heat it, but very rarely do we adjust the humidity. Why this omission? Undoubtedly it is partly because of widespread ignorance of the value of humidification. There is also a widespread antipathy toward humidification stemming from the association with the hot, steaming summer days. On a so-called dry, clear, brisk summer day, the kind we all like so much, the humidity ranges somewhere around 50%, which is ideal for the human body. Much drier than this is not so pleasant. The Sahara Desert, which is certainly too dry, averages 23% humidity. Many of our unhumidified homes in cold weather are even drier.
HITSCHLER WJ. Humidification Indoors in Winter. AMA Arch Otolaryngol. 1960;72(1):43–47. doi:10.1001/archotol.1960.00740010047008