Minimizing air leakage or infiltration is one of the most effective ways of reducing heating and cooling costs. In terms of energy efficiency, the less air that leaks into and out of a home, the better. However, a very tight home can have too little air leakage to provide good indoor air quality. Household products like aerosol sprays and cleaning solutions, cooking fumes, and moisture generated by showering and other activities can all be trapped inside the home and cause air quality problems. If any combustion-type appliances are present, additional air is required to ensure their proper operation. Balancing the needs for reduced energy consumption with those for indoor air quality is critical.

One way of balancing energy consumption with fresh air requirements is through controlled ventilation. Unlike uncontrolled infiltration of air, controlled ventilation can eliminate indoor pollutants and provide sufficient indoor air quality without a substantial "energy penalty." Obviously, any air which either leaks in from the outside or is brought in intentionally will have to be heated in the winter and cooled in the summer (if the home is air conditioned). But uncontrolled infiltration occurs 24 hours a day, while controlled ventilation methods can be utilized only as needed. There are two basic types of controlled ventilation; spot ventilation and whole-house ventilation.

There are certain areas within a typical home that require more ventilation than others.

Kitchens are a major source of cooking fumes, emissions from various household products, and moisture from cooking, dishwashing and other activities. Range hood vents which exhaust these contaminants to the outside can be used intermittently as the need arises. In order to be effective, the range hood should exhaust to the outside recirculating hoods filter out grease but do nothing to remove indoor pollutants.

Bathrooms are another area where odors and moisture create a need for higher levels of ventilation. All bathrooms, especially those with showers or Jacuzzis, should have a vent fan to exhaust excess moisture outside. Wiring the fan controls to the light switch ensures that the fan will operate when the bathroom is in use, but can cause the fan to run when not needed. The use of a timer to control the circuit is one way of preventing excessive use.

Laundries are another typical high-moisture area. All clothes dryers should be vented directly to the outdoors. Any attempt to "reclaim" the heat from the dryer may result in unacceptably high indoor moisture levels.

In all cases, the vents should terminate outside, and not in an attic or other unconditioned area where moisture can condense and cause damage. All vents should have a backdraft damper to minimize the infiltration of outdoor air when the vent is not being used.

In extremely tight houses, it is sometimes necessary to provide some degree of ventilation for the entire home. There are several ways of doing this. One is to introduce a certain amount of outdoor "make-up" air to the return side of the heating duct system. While this does increase the amount of fresh air in the home, the incoming air must be heated to the desired indoor temperature. This increases the load on the heating system.

An alternative to this method is the use of an air-to-air heat exchanger. This device can exhaust stale indoor air while bringing in fresh outdoor air, and transfer a large part (60%-80%) of the heat in the outgoing air to the incoming air. This reduces the additional load on the heating system by more than half.