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

Williamson Thermo-Flo OWT-4-T-S3-W – Oil-Fired Water Boiler with Tankless Coil, 125 MBH Input

The Williamson OWT-4-T-S3-W is a cast iron oil-fired boiler designed for residential hot water heating applications. Factory-equipped with a tankless coil for domestic hot water, this unit delivers reliable hydronic performance and integrated DHW functionality without requiring a separate storage tank.

Performance and Engineering

• Rated Input: 125,000 BTU/hr
• DOE Heating Capacity: 109,000 BTU/hr
• Net I=B=R Rating: 95,000 BTU/hr
• AFUE: 87%

The boiler is built with a wet-base, three-pass cast iron heat exchanger for increased thermal transfer efficiency and longer service life. The unit operates under standard chimney-vented natural draft and includes a factory-installed tankless coil, making it suitable for space heating with supplemental domestic hot water production.

Key Features

• Three-Pass Cast Iron Heat Exchanger: Maximizes efficiency by improving combustion gas contact with waterway surfaces
• Tankless DHW Coil: Factory-installed copper coil supplies domestic hot water on demand
• Flue Outlet: Rear flue connection simplifies venting to masonry chimneys
• ASME-Certified Heat Exchanger: Sectional cast iron design meets national code compliance
• Burner Plate: Includes provisions for Beckett AFG or other compatible burners

Installation Considerations

This boiler is intended for indoor installations and must be piped in accordance with industry standards for oil-fired hot water boilers. Proper draft control, flue sizing, circulator selection, and control wiring are essential to system performance. The unit ships as a packaged assembly for ease of installation but requires field connection of burner, controls, venting, and hydronic piping.

Dimensions: Compact footprint designed for utility rooms, basements, and mechanical spaces where floor space is limited. Total assembled height and service clearances should be reviewed in advance of final site placement.

Contractor Summary

• Packaged boiler with tankless coil included
• Oil burner sold and installed separately
• Standard rear-flue draft hood vent connection
• Ideal for retrofit projects needing combined space and DHW heating

Code and Compliance

• Constructed and hydrostatically tested to ASME Boiler Code Section IV
• Meets U.S. Department of Energy 87% AFUE minimum efficiency requirement for oil-fired boilers
• CSA certified

Summary

The Williamson OWT-4-T-S3-W is a field-proven oil boiler solution for hydronic systems with domestic hot water demand. With an integrated tankless coil, three-pass cast iron design, and 87% AFUE rating, this unit is engineered for reliable performance and long-term service life in residential heating environments. Designed with installer convenience in mind, it supports efficient, code-compliant setup in both retrofit and new construction applications.