Plants grow best at a temperature of about 70 degrees, and in a relative humidity of about 50-60%. Because plants increase humidity in their environment and quickly use available carbon dioxide, good air circulation and gaseous exchange are vital to successful hydroponic gardening. Additionally, excessive temperatures can damage plants and adversely affect their growth rate and yield. Hydroponic gardeners use blower fans to control temperature, humidity, and carbon dioxide availability.
Blower fans come in a range of sizes and are rated according to the amount of air they move per minute (a 245 c.f.m. blower will displace 245 cubic feet of air in one minute).
To choose the right fan, you need to know the size and average temperature range of the area. To achieve a cooling effect – which is often required - the fan should be able to change all the air in the room in less than three minutes (a 400 c.f.m. fan should be large enough for an area of 1200 cubic feet, unless the room gets unusually warm).