There are two primary firetube boiler designs: “wet back” and “dry back”. The basic difference between a wetback boiler and a dry back boiler is in the rear wall design. The wet back boiler has a rear wall that is surrounded by water, while the rear wall of a dry back boiler is lined with refractory. Since the heat from combustion is used for heating water, the wet back boiler design can be considered more efficient than the dry back boiler.

Wet Back and Dry Back Boilers Characteristics Compared

Wet Back BoilersDry Back Boilers
Cost/ExpenseHigher upfront cost; long term fuel cost savings, cost of ownership, and minimal downtimeLower upfront cost; simplistic design that is easier to service
DoorsLift off or split-hinged doors require no cool-down period; can be opened immediatelyHeavy, vessel-sized rear door requires space to open and cool-down period prior to opening
FootprintDoor design reduces floor space requirementsLarger floor space requirement for vessel-sized door functioning
MaintenanceNo costly refractory to maintain; internal pressure vessel maintenance can be more complexRegular inspection and periodic replacement of refractory required; simpler design
Rear TurnaroundImproves efficiency due to water absorbing burner heatRefractory wall reflects burner heat causing exterior radiation losses
Sealing KitsFewer seals; non-proprietary design for inexpensive and easy installationRequires multiple proprietary sealing kits for every inspection and vessel service
Tube SheetsSeparate tube sheets can expand and contract independently in response to temperature differentials between passesCommon tube sheet subject to extreme thermal stress in response to temperature differentials

 
Lathrop Trotter has extensive experience in developing both wet back boiler and dry back boiler applications. Our team can assist you in determining which boiler type will best serve your process, facility, and budget. Contact us to discuss your project!