In Canada the range of weather conditions is wide, from summer heat to winter cold, that the ventilation rate in livestock and poultry buildings can vary by a factor of at least 16 times. This plan explains alternative ways of obtaining this wide range in fan-ventilated buildings. The principle of stepped ventilation using several different-sized fans is explained and compared with control schemes using two-speed, multispeed or variable-speed fans. This plan also discusses other important considerations in choosing fans and controls for ventilating modern livestock and poultry buildings.