If you still have too much condensation even after reducing moisture production, or if indoor air quality is poor, you will have to increase the rate of ventilation or air change.

Ventilation systems work under two main categories: balanced and unbalanced. Unbalanced is most common where exhaust fans are used and replacement air comes from air leakage. This can result in reduced house pressures and limited success in ventilating the house properly. Balanced ventilation incorporates a system where exhausted air is replaced with a dedicated source of incoming air. This helps keep house pressures close to neutral and helps to ventilate the house more evenly.

Ventilation can be increased by

• installing ENERGY STAR® certified fans. It is worth buying quieter models designed for continuous use. Noisy fans tend not to be used much because they are annoying.

A somewhat effective ventilation technique involves having a contractor install a fresh-air duct with a damper to the return-air plenum of a forced-air system. The forced air system should be interlocked to appropriate exhaust fans to avoid pressurizing the house and pushing moisture into the building envelope. Outdoor air is drawn in by the suction of the furnace fan, mixed with house air and preheated by the furnace. The contractor should ensure that the cold ventilation air does not adversely affect the furnace in any way.

Open the damper in the outdoor-air duct just enough to prevent window condensation. It will have to be adjusted periodically through the seasons. Alternatively, a motorized damper with a humidistat control can open the damper only when the house becomes too humid.

Some ventilation systems are designed with a central exhaust fan with several ducts pulling air from the kitchen and bathrooms. Better yet, incorporate a heat recovery ventilator that typically recovers 70 percent of the heat from the exhaust air and transfers the heat to the incoming air. Central ventilation systems should be designed, specified and installed by a professional.