Landmark® Rooftop Units Standard Efficiency 2-6 tons. Packaged Heat Pump 60 hz and 50 hz. Performance Marked by Flexibility. Efficiency. New 7.5 to 25-ton high-efficiency units (gas/electric and electric/electric) Up to 13.0 SEER, 14.5 IEER and 12.7 EER; 2 to 25 tons (gas/electric and electric/electric) 2 to 20 tons (heat pump)