The Code Factor
Beyond the inherent health needs associated with mechanical ventilation, evolving energy code has forced the need for whole-house mechanical ventilation. For climate zones 3-8, 2009 IECC required building tightness of < 7 ACH @ 50 pascals. With the 2012 IECC standard this tightness requirement has increased to ≤ 3 ACH @ 50 pascals.
The ventilation implications of such tightness are self evident but are also explained through IRC Section R303.4 which states that whole-house mechanical ventilation is required when the air infiltration for a dwelling unit is < 5 ACH @ 50 pascals. Although IECC does not specifically reference ASHRAE, the commonly accepted requirements for residential ventilation are found in ASHRAE 62.2. Therefore, as the adoption of the 2012 IECC becomes more widespread, and ASHRAE 62.2 remains the industry standard, whole-house mechanical ventilation will become standard for all residential buildings in climate zones 3-8. This has broad implications for the HVAC industry, especially in climates deemed hot and humid that rely predominately on energy recovery ventilation (ERV) systems.
Moving forward, successful integration of 2012 IECC and ASHRAE 2013 will require education for building industry professionals and homeowners/building occupants. If not understood correctly, the relationship between home tightness and home ventilation can be perplexing. Why bring air inside if the goal is building tightness?
In truth, building tightness and ventilation are complimentary and both are necessary to achieve energy efficiency and healthy, indoor air. The relationship of building tightness and mechanical ventilation provide occupant control of indoor air and comfort. The variability of outdoor conditions, such as hot, cold, or polluted air, are controlled through mechanically operated ventilation systems that can be used when outdoor air conditions are good and not used when they are undesirable (i.e. high ozone days). Additionally, the use of mechanical ventilation supports energy efficiency because conditioned air has less likelihood of seeping out of the building – reducing total energy costs.