Optimum interior air quality has become an increasingly prominent concern in our work. Passive house interior air quality is pristine because highly filtered fresh air is constantly being exchanged with the interior air. The passive house standard requires filtration systems that achieve a MERV (Minimum Efficiency Reporting Value) rating of 12 or better - meaning dangerous contaminants have been removed from the air, including virtually all pollen and mold spores.

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), a widely respected international body responsible for building codes across the world, created the MERV Rating, which ranges from a value of 1 to 16, with the higher ratings meaning higher performance. Filtration systems undergo industry-standardized tests to earn their MERV ratings. Systems are tested with particles that fall into one of twelve size categories. The air is passed through the filtration system, and the effectiveness of the filtration media analyzed to see how well it removes pollutants in each size category. The smallest category of particles range from .3 to .4 micrometers and the larger particles range in size from 7 to 10 micrometers.

ASHRAE requires a minimum MERV Rating of 6 for residences. General commercial buildings and industrial workspaces typically use systems that score 5-8. According to the Environmental Protection Agency, the passive house design standard of MERV 12 or better usually applies to hospital laboratories.

Alongside air quality, energy efficiency is also of critical importance. In general, the better the air filtration in an air moving appliance, to more energy it takes, but higher quality equipment is available on the market that is both energy efficient and highly effective. The 'fresh air furnace' approach of passive house provides pristine interior air quality and operates at eighty to ninety percent less energy use than conventional furnace equipment.