ABSTRACT
Modern codes require ventilation, either natural or mechanical, but natural ventilation is quite limited and mechanical ventilation is used in most situations, except single-family dwellings. Convection is far less efficient than radiation because air has a low heat transfer coefficient, but it is used commonly in Heating, Ventilating, and Air-Conditioning (HVAC) systems because it has advantages (primarily for cooling) despite its weak overall efficiency. Unfortunately, cooling cannot be done effectively on a large scale using conduction or radiation, so it is necessary to use convection to blow cool air into occupied spaces. The International Building Code has strict rules for minimum opening sizes (relative to room sizes) and it limits natural ventilation to spaces directly adjacent to exterior walls (sort of-there are ways to provide natural ventilation to interior rooms too, although tricky to pull off). In order to heat, or cool, a building, it is necessary to maintain a temperature difference between outdoors and indoors.
