High-Efficiency Boilers Bryan Steam’s HE-AB Series of forced-draft, gas-fired “Flexible Water Tube” water boilers feature a guaranteed efficiency of 85%. The high-combustion efficiency results from a uniquely designed integrated, extended surface heat extractor and is supported by 7 sq. ft. of heating surface per boiler horsepower. The boilers operate at normal operating temperatures, without the expense or complications of special venting and/or condensing material. Boilers are available in six models with inputs from 900 MBH to 3,000 MBH.