Indirect water heaters may be the most important technology enhancement to enter the residential hot water industry in the past 30 years. Two key needs have driven demand for these useful and practical heating units: fuel efficiency and an ever increasing desire for more hot water. Hot tubs, large baths, multihead showers, and bigger homes with more bathrooms have increased America’s appetite for hot water, and indirect water heaters can satisfy the need faster than any other technology. Water Heating Choices Before the advent of indirects, the options for heating domestic potable water included conventional direct-fired units or boilerintegrated “tankless coils.” Direct-fired water heaters (electric-, gas-, or oil-fired) are by far the most