Efficient Comfort. According to Triangle Tube, the Prestige Solo Condensing Boiler is one of the most efficient and environmentally friendly heating systems on the market. Its stainless steel heat exchanger operates at up to 96 percent efficiency, and when demand is low the boiler adjusts its firing rate to 25 percent of its rated input, resulting in fewer on/off cycles. It comes in five sizes with outputs ranging from 60,000 to 399,000 Btu per hour. The most popular Solo 110 model (110,000 Btu) costs about $3,600. Triangle Tube, 856/228-8881, triangletube.com
