For years the weatherization industry calculated whole-house ventilation by ASHRAE standard 62-1989. This standard was mercifully simple compared to the new ASHRAE standard 62.2-2010. The BPI building analyst training still trains to the old 62-1989 standard. That standard says very little: Provide 0.35 natural air changes per hour but not less than 15 cfm per person. Kitchens need 100 cfm and bathrooms need 50 cfm of intermittent ventilation. Air sealers stopped air sealing when they reached the building tightness limit (BTL) or building airflow standard (BAS). They assumed that natural ventilation provides good acceptable air quality.
ASHRAE 62-1989 was mainly a standard for commercial buildings and the residential standard, just described, was a minute part. Building scientists calculated n-values to convert our blower-door values into natural air-change rates. They created a map and a table to establish our building tightness limit (BTL) or building airflow standard (BAS). Many weatherization agencies and home performance contractors still evaluate ventilation using 62-1989.
ASHRAE 62.2 is one of the most controversial ASHRAE standards ever developed. All new and most existing homes now require fans for whole-house and local ventilation. 62.2 is also complex and confusing, but I think it’s here to stay. Describing 62.2 in a few sentences is difficult but I’ll try anyway.
You determine whole-house ventilation fan’s capacity from a by taking 1% of floor area in square feet and add 7.5 CFM per bedroom. Then you figure local ventilation based on 100 cfm for kitchens and 50 for bathrooms with a credit of 20 cfm if the kitchen or bathroom has an opening window. You can add extra capacity to the whole-house ventilation fan to avoid installing a separate local ventilation fan. You can do a blower door test and apply a revised n-value to determine an “infiltration credit” which reduces the whole-house ventilation fan’s required capacity.
When you comply ASHRAE 62.2 on an existing home, the fan installation costs from $400 to $1000. This cost takes a significant chunk out of limited energy-conservation budgets. ASHRAE requires a lot of training too. Really, you should measure the ventilation fan airflow too.
Some air-sealers still believe that the old 62-1989-optimized natural air leakage provides adequate ventilation. Others reject this assumption and insist that homes be sealed to the maximum possible level and ventilated mechanically according to ASHRAE 62.2.
Air-sealing success depends on the home’s difficulty, the air-sealing budget, as well as the knowledge, grit, and persistence of the air sealers. Success varies from no measurable leakage to a very tight home. The heating-and-cooling energy savings tends to follow the air-sealing success. Although insulation is arguably as cost-effective as air-sealing, air leaks missed by the air sealers reduce insulation’s effectiveness.
Here at Saturn, we agree that effective air sealing is essential to saving heating and cooling energy. However, the ASHRAE 62.2 is too complex and needs to be simplified.