The A. O. Smith ProLine XE combination boiler’s service-friendly compact design offers professional contractors easy installation, setup and maintenance, delivering immediate hot water and comfortable space heating for homes. The combi boiler’s user-friendly interface — featuring a backlit LCD display that provides text-based diagnostic information — is one of the product’s leading differentiators. Featuring outstanding energy-saving performance, the ProLine XE combi boiler can deliver up to 4-gal. of hot water per minute and immediately stops non-heated air from circulating when it alternates from space heating to domestic hot water mode.  A. O. Smith.