With a maximum output of 9.8 gpm, the R98 Tankless Water Heater uses either natural or propane gas. Providing domestic hot water and hydronic heat, it has a 10-year heat exchanger warranty and 20-year life expectancy. The water heater has a compact, lightweight design and maintains its temperature for continuous hot water, the manufacturer says. 800-621-9419. www.foreverhotwater.com.