Sites vary, but most mention a median range of between 30-40% humidity.
During extremely cold weather, your home loses humidity to the
outdoors and may drop as low as 5%. By comparison, typical humidity in
the Sahara Desert is about 25%! Generally, one does not want to have a
home humidity any lower than 30%. Optimal comfort is considered to be
achieved at 40-55% humidity. Nosebleeds also occur in hot dry climates
with low humidity, or when there is a change in the seasons.
Indoor relative humidities should be kept above 30% to reduce the
likelihood of the occupant’s nasal passages drying out,
Humans can be comfortable within a wide range of humidities depending
on the temperature—from thirty to seventy percent—but ideally
between 50% and 60%. Very low humidity can create discomfort,
respiratory problems, and aggravate allergies in some individuals. In
the winter, it is advisable to maintain relative humidity at 30
percent or above. Extremely low (below 20%) relative humidities
may also cause eye irritation.
Keep the heat low [60°F (16°C) to 64°F (18°C)] in sleeping areas