This can waste energy, especially if the drying air is heated. Favorable Conditions for Air Drying Table 1 indicates when outside air can be effectively used to dry a room or house. Heat may be necessary to maintain the indoor air temperature when using outside air for drying. The results in Table 1 assume that the indoor temperature is maintained at the levels listed. When the outside air temperature drops below freezing care must be taken to prevent water pipes from freezing where cold outside air is brought into the house.
Cold air has a very low moisture-holding capacity.
Figure 1 shows how much the moisture holding capacity of cold air increases when it is brought into a house and heated. This increase in moisture-holding capacity enhances drying. As the outside temperature decreases, outside air ventilation drying always becomes the recommended drying method. The last line in Table 1 lists the outside air temperature below which ventilation drying is always recommended, irrespective of outside relative humidity. Care must be taken to prevent water pipes from freezing when below freezing outside air is brought into the house.