Air sealing work seals openings in the building enclosure that may have previously been relied on for natural or passive ventilation in the home. Inadequate ventilation can lead to indoor air quality concerns and moisture problems, and therefore a properly functioning and sized mechanical ventilation system is necessary. Further information can be found in numerous resources on ventilation system design including Chapter 18 of the new Canadian Home Builders' Association Builders' Manual, and TECA's Quality First Ventilation Guidelines (see Resources at the end of this Guide).