A practical method for circulating air is necessary. An ERV provides moisture control, indoor air quality, and energy recovery. The ERV brings fresh, outside air into the house while pumping stale, indoor air outdoors. The ERV transfers energy by passing both air sources very closely together in separate networks of ducts. The air doesn't mix, but the temperatures do.
Some models have a pollution sensor built into the switch to immediately prompt an air exchange.
Although it is very energy inefficient, a small supply of fresh air enters the home. This is not the case with recently built homes. Insulating products like house wraps that protect outside sheathing, high quality fiberglass insulation and energy efficient windows all create a tight seal. The house has no fresh air exchange at all. At the same time, moisture decays building materials.