WATERFURNACE. Capable of 150-degree F water output, the 5 Series 502W12 makes upgrading to a geothermal system easier, especially when the replacement system must work with existing cast-iron or baseboard radiators, the firm says. The unit uses two high-efficiency compressors for low-cost operation while compressor blankets, double-isolation mounting plates, and a discharge muffler ensure a quiet system. It exceeds Energy Star requirements and qualifies for a 30% federal tax credit. 800.436.7283. www.waterfurnace.com.