Oil-Fired Water Boiler, Tankless Heater 125 MBH, 87% AFUE, Series 3

Williamson OWT-4-T-S3-W – Oil-Fired Water Boiler with Tankless Coil, Series 3

The Williamson OWT-4-T-S3-W is a cast iron, oil-fired water boiler engineered for hydronic heating systems requiring integrated domestic hot water capability. This Series 3 model is equipped with a tankless coil and rated at 125 MBH input, delivering 87% AFUE efficiency. It is built to handle medium-load residential applications where long-term reliability and service accessibility are priorities.

Engineered for Performance and Service Life

• Boiler Type: Oil-fired water boiler with tankless domestic coil
• Input: 125 MBH
• AFUE: 87%
• Net AHRI Water Rating: Approximately 109 MBH (varies slightly by setup)
• Heat Exchanger: Cast iron, sectional construction
• Combustion: Beckett AFG burner (factory-shipped)
• Tankless Coil: Domestic hot water coil integrated into the front section
• Ignition: Interrupted electronic ignition

Key Mechanical Features

• Factory-assembled cast iron block with push nipple design for hydraulic integrity
• Recessed target wall and swing-out burner door for full chamber access
• Top or rear flue outlet options (pre-cast), simplifying vent layout flexibility
• Jacketed with pre-installed insulation to minimize standby heat loss
• Service switch and circulator pump (factory-wired)

Installation Guidelines

The OWT-4-T-S3-W is a floor-mounted, non-condensing boiler designed for closed-loop hot water systems. It requires standard venting through a chimney and must be installed in accordance with local code and NFPA 31 standards. Proper sizing of the tankless coil and hydronic zones should be verified for the application. Field assembly includes burner mounting, vent connection, flue damper installation, and wiring termination.

Installation is best performed by licensed HVAC or plumbing professionals due to oil combustion tuning, flue draft measurement, and zone control integration. Fuel line routing, combustion air requirements, and condensate management (if indirect-fired DHW tank is added) must also be considered.

Application and Use Cases

• Residential heating with integrated DHW demand via tankless coil
• Single-family homes or light multifamily with limited space for indirect tanks
• Direct replacement in legacy hydronic systems requiring a cast iron block

Advantages for the Field

• All controls and service access on one side—ideal for utility rooms or tight installations
• Reliable domestic hot water without a separate tank
• Simple flue damper and circulator wiring reduces setup time
• Designed to operate with standard oil burners and widely available service parts

Summary

The Williamson OWT-4-T-S3-W provides a compact, field-proven solution for oil-fired residential water heating systems with domestic hot water demand. With cast iron durability, efficient operation, and integrated coil, it supports contractors requiring a straightforward, long-lasting installation. It is best suited for traditional hydronic loop configurations where oil is the primary energy source.