To investigate the cause of dryness in the air, go over your posts in the past about sweating windows and wet basements. Tie them together as a field of study about warm air heated houses and hot water heated houses, especially new construction in the past five years. Look at the psychometric charts and investigate the relative humidity of 70F air and 120F air. Investigate the differential pressure produced from room to room and the resulting increaesed air change rates due to different pressures in areas of a building due the air-moving fans - and the dry air introduced in winter to make up the loss from ducts. ASHRAE has done so. A fixed opinion may change.