LP gas or any heating system , electric, Ng, oil, does not add humidity
on it own , if it does its emitting Co and you would be sick.
Humidifiers add humidity, cooking, showering, etc. Windows condense
because it is the coldest area of the house, poor designs have little
insulation value. Dual pane does not mean high insulation, CDF is
condensing factor, a rating Pella scores poorly on compared to Anderson.
You have not determined humidity is high and its not just poor glass or
a humidifier or tight house. If windows are sealed shut as you seem to
indicate than how do you open the casements. Start with a calibrated
analog humidisat, one you set-calibrate yourself, or a good digital and
see where you are. If you have a humidifier , turn it down till