Successful production requires uniformity in many areas including ventilation. Air velocity and turbulence are two important ventilation factors. The interactions of these factors have an influence on pig comfort/stress as well as disease. Studies have resulted in the development of a temperature vs. airflow velocity chart that suggests specific airflow rates (in feet/minute) that do not hinder productivity. As the temperature of the barns fluctuates the pigs will adjust their feed intake accordingly. It is believed that the greatest intake of net energy along with peak conversion occurs just above the lower critical temperature. When analyzing ventilation it is important to take into account volume, distribution, and control of air. Recommended ventilation rates are simply calculated by multiplying the number of animals in the house by the recommended rate. The distribution system will provide sufficient mixing of fresh air with appropriate maintenance. A common method of monitoring the control of air is via a sensor inside of the room in question. These can help to make control decisions. Most of the ventilation problems occur during cold or cool weather when ventilation rates are low. Air quality can be poor because of under ventilation. If relative humidity is high, other contaminants are usually above the threshold values as well. A suggested priority for ventilation testing would be temperature and humidity, air distribution pattern, ammonia, carbon monoxide, carbon dioxide, and dust.