Oil-Fired Water Boiler, No Tankless Heater 125 MBH, 87% AFUE, Series 3

Williamson OWB-4-T-S3-W – Oil-Fired Water Boiler, High-Efficiency Cast Iron, 125 MBH

The Williamson OWB-4-T-S3-W is a 4-section, oil-fired cast iron water boiler engineered for residential hot water heating systems. With a gross output of 109 MBH and an input rating of 125 MBH, this model delivers reliable hydronic performance and an 87% AFUE efficiency rating. The unit is equipped with a factory-installed circulator and service switch, ready for integration into multi-zone baseboard or radiator systems.

Performance & Construction Highlights

• Fuel: Oil-fired, Beckett NX-compatible (burner not included)
• Gross Output: 109 MBH
• Net I=B=R Rating: 95 MBH
• AFUE: 87%
• Boiler Type: Water (non-steam)
• Number of Sections: 4
• Flue Connection: 6" diameter
• Relief Valve Rating: 30 PSI
• Circulator: Taco 007 pre-installed

Design and Functional Benefits

• Cast Iron Heat Exchanger: Offers excellent heat retention and resistance to thermal shock for long-term reliability
• Accessible Layout: Features a swing-out burner door and removable front panels for straightforward service access
• Hydronic Compatibility: Suited for closed-loop baseboard, panel radiator, or radiant floor applications
• Knockdown Design: Available disassembled for easier transport through tight clearances (assembled version also offered)

Installation Parameters

Installation requires a qualified oil technician familiar with proper nozzle sizing, combustion testing, and venting in compliance with NFPA 31. This model supports chimney venting through a barometric damper and must be connected to an appropriately sized oil tank. Electrical wiring for the circulator and service switch is pre-configured at the factory.

Key Dimensions & Connections

• Height: 35-1/2"
• Width: 19"
• Depth: 25-3/4"
• Water Inlet/Outlet: 1-1/4"
• Flue Outlet: 6" diameter
• Electrical: 120V service switch factory-mounted

Professional Use Case

The OWB-4-T-S3-W is a dependable option for light-duty residential replacement or new installs requiring oil-fired equipment. Its compact footprint allows for retrofit flexibility, and the included circulator and low-limit control streamline hydronic loop integration. Beckett burner pairing and appropriate draft setup are required to meet factory performance specifications.