A full line of high-efficiency gas boilers includes the Evergreen, Ultra Series 4, GV90+ cast-iron, and the AquaBalance Series 2. All units operate with natural or propane gas and have the latest hydronic heating technology to provide heating comfort and energy savings. Evergreen line is available in six sizes from 70 to 399 MBH input. Ultra Series 4 boilers have a nanotechnology coating that works like Ultra Armor, protecting the unit from buildup in the heat exchanger. The GV90+ offers an AFUE rating of 91%. AquaBalance Series 2 units have an energy efficiency of 95%.