From a local news article:
"You have to strike a peaceful balance between what feels good (40 to 60 percent relative humidity) and what is best for the house (20 to 40 percent). You want to add enough moisture for some comfort without causing excessive condensation on windows, in the attic and wall interiors. Monitoring window condensation is a quick check."
We have a humidifier which goes with the furnace, but spouse had a bleeding nose so we increased it. Yesterday, as the temp. tank from 20 to -9, with a windchill of -35 and a major snow storm, all of a sudden I noticed that all the windows were soaked in moisture. We lowered the humidifier and started toweling the windows. We also left open all the drapes and the shades.
The humidity in our bedroom is still 38 which is way too high.
On the other hand, we installed a gas insert in the fireplace, so have not been using the furnace much and I wonder whether the lack of dry air have kept humidity up.
The local paper recently has published a guideline which, until recently, was exactly what we had
Moisture rules
December 3, 2008
MOISTURE RULES
To protect your home's structure, if the outside temperature is:
• 20 to 40 degrees, indoor humidity should be no more than 40 percent.
• 10 to 20 degrees, indoor humidity should be no more than 35 percent.
• 0 to 10 degrees, indoor humidity should be no more than 30 percent.
• Minus-10 degrees to 0, indoor humidity should be no more than 25 percent.
• Minus-20 to minus-10, indoor humidity should be no more than 20 percent.
• Lower than minus-20, indoor humidity should be no more than 15 percent.
http://www.startribune.com/lifestyle/35476744.html