Ventilation.

Ventilation is the process and practice of keeping indoor air in good conditions, because it helps protect your health and you home. There are two basic approaches to ventilating your home: 1)spot ventilation for localized pollution sources; and 2) general ventilation to dilute pollutants from sources that exist in many locations or more from place to place. General ventilation mixes fresh outdoor air with stale indoor air to lower the concentration of pollutants.. General ventilation can provided in two ways: exhaust – only and supply and exhaust. With exhaust-only ventilation, exhaust fans pull stale air out of your home while drawing fresh air in through cracks, windows, or fresh air intakes. With supply-and exhaust ventilation, exhaust fans pull stale air out of the house while intake fans blow in fresh air. Natural ventilation systems rely on pressure differences to move fresh air through buildings. Unlike true air-conditioning, natural ventilation is ineffective at reducing the humidity of incoming air. In homes not mechanically cooled the temperature can be controlled to some extent by the use of attic fans. These fans are usually ceiling mounted in a central hallway so that outside air is pulled through open windows and exhausted through the attic. Power ventilators have the advantage of providing good ventilation even when there is no wind. Whole-house ventilation systems are usually classified as:

v exhaust ventilation if the mechanical system forces inside air out of the home,

v supply ventilation if the mechanical system forces outside air into the home,

v balanced ventilation if the mechanical system forces equal quantities of air into and out of the home.

Exhaust ventilation system is composed of a single fan connected to a centrally located, single exhaust point in the house. One concern with exhaust ventilation systems is that they may draw pollutants, along with fresh air, into the house. Supply ventilation system has a fan and duct system that introduces fresh air into usually one, but preferably several rooms of the home that residents occupy most often. Balanced ventilation systems introduce and exhaust approximately equal quantities of fresh outside air and polluted inside air. Balanced ventilation systems are appropriate for all climates. Fresh air supply and exhaust vents can be installed in every room, but a typical balanced ventilation system is designed to supply fresh air to bedrooms and living rooms and exhaust air from rooms where moisture and pollutants are most often generated. A heat-recovery unit reduces the heating and cooling costs of ventilation by transferring heat from the warm inside air being exhausted to the fresh but cold outside air in the winter, and vice-versa in the summer.