The Series 500 four-pass wetback Scotch marine boiler from Hurst Boiler & Welding Company is designed for optimum fuel efficiency with no heavy refractory back doors or baffles to replace or maintain. It has independent tube sheets with uniform temperatures, eliminating premature tube failure and cracks in the tube sheet. It has capacities from 30 to 2,000 hp, with 15 psi steam and 30 psi water (60 psi water optional). No field assembly is required. UL Listed boiler/burner packages come with fully assembled, prepiped, prewired and pressure-tested gas trains. 800/666-6414; www.hurstboiler.com.