A package multiple pass flexible water tube boiler for converting water to steam. The boiler having an enclosure and diagonally offset upper and lower drums. The drums are connected by a series of staggered or offset water tubes. The water tubes comprise two sets of repeating tubes that are bent to substantially similar but not identical designs. The staggered tube arrangement optimizes heat transfer and minimizes the footprint of the unit.

A package multiple pass flexible water tube boiler for converting water to steam. The boiler having an enclosure and diagonally offset upper and lower drums. The drums are connected by a series of staggered or offset water tubes. The water tubes comprise two sets of repeating tubes that are bent to substantially similar but not identical designs. The staggered tube arrangement optimizes heat transfer and minimizes the footprint of the unit.