"The red areas demonstrate that this house is losing most of its heat through the windows. Generally, heat loss occurs in three ways: infiltration, natural ventilation, and mechanical ventilation.
“Infiltration” occurs when outdoor air flows into the house through openings, joints, and cracks in walls, floors, and ceilings, and around windows and doors.
In “natural ventilation”, air moves through open windows and doors.
“Mechanical ventilation” systems circulate fresh air using ducts and fans, rather than relying on airflow through small holes or cracks in a home's walls, roof, or windows.
Air movement associated with infiltration and natural ventilation is caused by air temperature differences between the indoors and outdoors, and by the wind.
The air exchange rate, which is the rate at which outdoor air replaces indoor air, can be low and pollutant levels can increase when there is little infiltration, natural ventilation, or mechanical ventilation." from Milguard = Full story >