In North America, there are ~140 million homes and 4 million public buildings. More than one fifth of theenergy use in Canada is used to condition air whether from the cold in much of Canada or providecooling and heating where summers are hot and humid and winters are cold. To reduce greenhousegases and improve housing affordability, this energy use needs to be reduced. In 1981, the Federal andProvincial governments understood that science was needed to inform building codes in relation tooccupant health. Ventilation standards used in North America were developed during the late 19thcentury from studies done mainly in schools. Modern studies of ventilation rate and health effects inpublic buildings indicate that relative risk for increased respiratory disease and absenteeism becomessignificant around 14 L/s per person. Most of this work has been done in public buildings. In Canada,there has been interest in ventilation questions for residential housing in relation to comfort, diseasetransmission and relationships of ventilation to dampness and pollutants mainly derived from vehicletraffic as well as endotoxin. Considering new homes with heat recovery ventilators, occupants reportedimprovement over 1 year in the symptoms of throat irritation, cough, fatigue, and irritability incomparison with control new home occupants. Homes that have low per person ventilation rates, and,those that are air leaky are prone to dampness with the associated increased risks of asthma andupper respiratory disease. In the most under-ventilated homes in Canada (in the far north), increasedinfectious disease has been observed in infants. Lastly, both gaseous and particulate air contaminantsinfiltrate homes. This is affected by ventilation and other aspects of system design and appears tomodulate allergic responses. New studies are needed on the effect of ventilation on health to preventnegative effects on population health consequent to changes in energy codes for residential homes.