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Aldrich Boilers – A3S4 Series

A3S4 Series – Through the Door Design

Capacities: 15 – 250 BHP
Models up to 125 BHP Fit Through 36” Doorway
Inputs from 6000,000 to 10,100,000 BTUH
Outputs from 500,000 to 8,369,000 BTUH
Designed to Meet the Needs of Boilermakers


Aldrich Company manufactures three pass and vertical firetube steam boilers for low pressure applications. The Classic Series modified Scotch Marine “Scotch Box” boiler is designed to fit through a standard doorway.

  • Modified Three-Pass Scotch Marine “Scotch Box” Boiler
  • Fuels: Gas, Oil, Combination Gas/Oil, Digester Gas
  • 15 PSI Steam / 30, 40, 80, or 150 PSI Water Design
  • 83 – 88% Efficiency
  • “U-Type” Flex Joint
  • Thermal Shock Resistance
  • Welded or Expanded/Flared Tube Attachment
  • Water Surrounded Cylindrical Furnace For Highest Heat Transfer
  • Water Cooled Reversing Chamber 4-Sided Wetback
  • Insulated Boiler with 18 Gauge Boiler Jacket


The “Classic” Series combines the features of Scotch Marine and Firebox boiler designs to produce a durable wetback boiler. Each boiler is constructed with a water surrounded cylindrical furnace for highest heat transfer. The reversing chamber is water cooled on the front, top, bottom, and sides. Models up to 125 boiler horsepower fit through standard 36” doorways.

The “Classic” Series boilers are built, inspected and stamped in accordance with ASME Code Section IV. Boilers include extra heavy 12-gauge tubes for extended life. Boilers may be provided with either extended/flared tube attachment or all welded attachment.

U-Type Flex Joint:
The U-Type flex joint burner port minimizes the effects of differential stress as the boiler furnace expands at a greater rate than the firetubes during operation. The U-Type flex joints distributes the expansion force among multiple perpendicular surfaces reducing the potential of damage.

Removable Smokeboxes:
Both the front and rear smokeboxes include flange attachment for ease of access to firetubes. Firetubes are easily accessible from either the front or rear of boiler.

Rear Access Door:
The “Classic” Series boilers are equipped with a rear access door providing access to both the furnace and first pass of firetubes. The rear access door utilizes high temperature ceramic fiber insulation modules.

Turbulators insure positive furnace pressure necessary to achieve the highest non-condensing combustion efficiencies in the industry.


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