Laboratory animal facility ventilation rates and ventilation system designs are greatly influenced by the recommendations given in the "Guide for the Care and Use of Laboratory Animals" (ILAR, 1985). The guide dictates high ventilation rates of 10-15 air changes per hour (ACH) in hopes of providing a good air environment for both the human workers and the caged animals. The workers want an environment with tolerable levels of odor, dust, and allergens, and the high ventilation levels of 10-15 ACH can be traced back to the desire to provide an odor free environment for the workers. The well-being and experimental response of the laboratory animals depends greatly on the air quality and thermal environment. However, the high room ventilation rates do not ensure that cages are receiving adequate ventilation to provide a good micro-environment for the animals.