The Tappan iQ Drive® FT4BG split-system heat pump and iQ Drive R6GI gas pack have inverter technology. The systems reach higher levels of energy efficiency through modulation and dramatically reduce sound levels for a quiet, comfortable home. The split-system heat pump reaches 19 SEER and 10 HSPF. It is available in 2 to 5 ton capacities. The gas pack is rated for 20 SEER cooling efficiency and 81 percent AFUE heating. The packaged system is available in 2, 3, 4, and 5 tons. The power to modulate is a key feature of the energy-efficient systems. They modulate from approximately 40 to 118 percent capacity in five steps, meaning that they are able to fluctuate between different output levels so that they use just enough energy to meet the demands on the home. The systems are also as quiet as 59 dBA. The heat pump and gas pack work with most two-stage thermostats. According to the company, there's no need for shielded cable during installation.