Cooling efficiencies are based upon direct expansion air conditioning, but are typically limited to a SEER of 12. Heating efficiencies depend upon electric resistance or boiler efficiencies. Boiler-based units are less expensive to operate than electric resistance units and can use the energy efficiency options identified in that section. Occupancy control can reduce demand, either centrally or within each room. Economizer controls can provide free cooling when outdoor air conditions permit.