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Gaseous contaminants may be controlled through continually operated exhaust fans or heat recovery ventilators (HRV) and energy recovery ventilators (ERV), both of which bring in fresh air from the outside, dilute contaminants and exhaust them.

Any number of high quality and widely available exhaust fans can be used for continuous use. Two very important aspects of fans designed for continuous operation are that they are quieter and more energy efficient than fans designed for intermittent use. The sound level of a product which will run continuously is much more important than it is for an intermittent exhaust fan.

By recovering the energy to heat in the winter and cool in the summer, an HRV can provide clean fresh air continuously while helping to keep energy costs low. An ERV will also recover moisture from the exhaust stream.

An ERV is the best solution if the annual cost of operation is a consideration, although it may take several years to pay back its higher initial installation cost. Because the ERV has an energy transfer (enthalpic) core, excessively low humidity is less likely to be a problem, thereby reducing the need for a separate humidifier and its considerable energy cost. HRVs and ERVs also provide balanced ventilation that avoids problems associated with the home’s pressurization or depressurization.

The use of a dedicated exhaust fan, HRV or ERV to provide low-level general, effective ventilation at an energy efficient rate must be supported with intermittent bath and kitchen ventilation for source control.

Continuous ventilation equipment must run whenever the house is occupied, especially during spring and fall. Windows may be opened, but unless there is a breeze to ensure ventilation, it is easiest and best to just let the unit run, even if windows are open. Incidental (or accidental) ventilation is driven by natural forces and they are least effective when the temperature difference between indoors and outdoors is the smallest. That is when mechanical ventilation is needed the most.