Variable speed fans operate on a simple principle: they are able to spin at different speeds depending on the heating and cooling needs of your home or business. Usually, they operate at lower speeds, delivering a steady, reliable stream of warm or cool air. When conditions become more extreme, the fan speed increases so that the HVAC system can meet increased demand, guaranteeing that even on the hottest days or coldest nights your comfort needs will be met. Older HVAC systems simply switch on or off. Newer, variable speed HVAC systems also lower your electric bill by only using the energy needed to heat or cool your home or business at any given time.