Ammonia from manure and moisture from swine respiration can combine to reduce air quality and increases odor when a room is not sufficiently ventilated. As pigs increase in size the moisture they contribute to the air will increase, so ventilation should be increased as well. Keeping the humidity below 70% and the ammonia below 20 ppm can result in heat loss during winter months, and the ventilation rate may not maintain air quality if it is based on temperature. An alternate heat source should be used in winter months to provide heat while the ventilation is used for air quality. Two of the most common problems with ventilation are not ventilating to control humidity and not using a heater. Heat exchangers or passive solar energy collectors are two options to provide heat while saving money.