How energy efficient are Green Mountain gas-fired boilers?

Green Mountain Boilers rates its products as "mid-efficient." The Utica-based manufacturer has a product line of two gas-fired water boilers and one gas-fired steam boiler.

The Green Mountain gas-steam series boiler unit features an annual fuel utilization efficiency of up to 82.7 percent; this percentage rating is a ratio that describes how many British thermal units of heat the unit produces per 100 units of fuel input. Thus, the Green Mountain gas-water series boiler, with an AFUE rating of 82 percent, produces 82 BTU of heat per 100 BTU of gas used by the unit. The company's most efficient unit, the PVB Series II gas-fired water boiler, has an AFUE of approximately 84.4 percent.