Furnaces are incorporated into forced-air systems that can supply a mix of outdoor air and "return" air. These systems can also use condensing units and evaporator coils to provide cooling. Efficiencies are typically measured by the Annual Fuel Utilization Efficiency (AFUE) for furnaces up to 225 kBtu/h, and by thermal or cumbustion efficiency for larger furnaces. Baseline furnace efficiencies of oil and gas (natural and propane) units are typically around 80%. With high efficiency systems, this can rise to approximately 88% for non-condensing furnaces, and as high as 95% with condensing furnaces. Energy efficiency measures in furnace systems include variable speed control of ventilation fans (tied to temperature, pressure, or carbon dioxide sensor output) and NEMA Premium^TM fan motors.