the 'thermal efficiency' is sometimes called the energy efficiency. in the united states, in everyday usage the seer is the more common measure of energy efficiency for cooling devices, as well as for heat pumps when in their heating mode. for energy-conversion heating devices their peak steady-state thermal efficiency is often stated, e.g., 'this furnace is 90% efficient', but a more detailed measure of seasonal energy effectiveness is the annual fuel utilization efficiency (afue).