Boiler-system design often addresses energy efficiency and
emissions, but seldom boiler footprint as well. A recently
formalized partnership between a Europe-based provider of
heating and ventilation technology and a U.S.-based boiler
manufacturer has resulted in an extended-heat-transfer-surface
boiler tube for use in both hot-water and steam boilers. The
tube increases heat transfer over a bare boiler tube by a factor
of five, allowing a dramatic reduction in both tube count and
footprint. The tube is installed in more than 10,000 hot-water-
boiler systems throughout Europe. Several years ago, it was
introduced in the United States with the release of a
condensing-boiler product line. Recently, it was introduced into
several steam-boiler designs. Inside the carbon or stainless-
steel tube is a finned aluminum-alloy insert (Figure 1).
Efficient heat transfer is the result of three factors: The high
heat conductivity of the aluminum alloy. The finned, ridged
design, which greatly increases heat-exchange surface