ENERGY RECOVERY VENTILATION
As houses become more and more airtight, it will become more and more common to see energy-recovery ventilators in homes. Air-tightness is a result of improved building practices and products, like air barriers, better seals on windows and doors, panelized construction, air-sealing procedures, and sealed-combustion furnaces and water heaters.

People like the benefits of air-tightness in their homes, including improved energy efficiency, fewer uncomfortable drafts, and the exclusion of noise and dust from the outside. What is lost, however, is the natural infiltration that used to carry away the indoor pollutants: carbon dioxide, formaldehyde, cool-weather moisture, cooking odors, and other gases coming from building materials and cleaning compounds.

In old houses, natural infiltration was so effective in removing these pollutants that often, more water was carried away than was generated in the home by the breathing, washing, and cooking of the occupants (thus the need for additional humidification in older homes). Nowadays, that water isn't removed from the new, tighter houses, unless a ventilation system is in use, so windows can be damaged by the moisture build-up. With "run-away humidity" insulation loses its effectiveness, and in severe cases, structural damage can occur.

Even though we do not know everything about pollutants in homes yet, there is real concern. Formaldehyde originating in various board products and insulations caused significant problems in the building products industry. Changes in product formulations to try and reduce the amount of formaldehyde because of possible health concerns have only been partially successful. There are other pollutants that may be of concern. A common one is carbon dioxide, which in excess concentrations can cause lethargy and lack of alertness. We all generate carbon dioxide by breathing, but it can be very effectively controlled by air-to-air heat exchangers. A ventilation system provides better indoor air quality.