As changing technology improves the methods and materials involved in residential building, studies are indicating the need for a home ventilation system. New homes are currently being built that greatly improve energy efficiency by sealing these homes off from the outside. The same is happening to older homes. New windows and doors help to improve the energy efficiency of these homes. The negative side effect of all this is that homes can no longer breathe in a manner that allows stale, damp, contaminated air out and a good supply of fresh air in. This lack of airflow through the home is being linked to severe health concerns and a general deterioration of the value of the home.