This house suffered from inadequate ventilation in some rooms, which was so noticeable during the winter months that the air conditioner was often used to reduce humidity and the sense of "stuffiness." A whole-house heat-recovery ventilation system was added, with a priority on ventilating these stuffy rooms, to very good effect.
This all-electric house was built extremely air-tight -- most of the ventilation air we found was coming down the chimney flue! We recommended a ventilation system, but the homeowners declined the expense. Similarly, a majority of their electricity consumption was due to the hot tub, but they were not willing to shut it down for part of the year.