Oil-Fired Water Boiler, Tankless Heater 133 MBH, 87% AFUE, Series 3

Williamson OWT-3-T-S3-W – Oil-Fired Water Boiler with Tankless Coil, 98 MBH Input, 87% AFUE

The Williamson OWT-3-T-S3-W Series 3 oil-fired hot water boiler is built for hydronic systems requiring integrated domestic hot water production. With a 98,000 BTU/hr input and an 87% AFUE rating, it delivers high thermal efficiency and steady, reliable operation for residential and light commercial heating loads.

This unit is equipped with a factory-installed tankless coil, allowing for continuous hot water production without a separate storage tank. Constructed with cast iron heat exchanger sections, the boiler is engineered for durability and consistent performance over a long service life.

System Highlights

• Integrated Tankless Coil – On-demand domestic hot water production without external tanks.
• Cast Iron Construction – Rugged design with three heat exchanger sections for long-lasting reliability and even heat transfer.
• Factory-Included Circulator – Shipped loose Taco 007 circulator supports efficient system flow.
• Low Water Cut-Off – Enhances system safety by preventing operation during unsafe water level conditions.
• Rear Flue Discharge – Rear outlet standard with optional top-venting kit for installation flexibility.

Performance Specifications

• Model: OWT-3-T-S3-W
• Fuel: #2 Heating Oil
• Input: 98,000 BTU/hr
• Heating Capacity: 86,000 BTU/hr
• Net AHRI Water Rating: 75,000 BTU/hr
• AFUE: 87%
• Sections: 3
• Weight: ~560 lbs
• Dimensions: 20.25" W x 13.75" D x 35.63" H

Professional Considerations

This unit is intended for installation by licensed professionals due to the complexity of configuring oil burners, venting systems, and zone piping. The system ships with core safety and operating controls, including temperature limit, pre-wired harness, and serviceable burner swing door. The included circulator is field-installable for supply or return piping based on site requirements.

Chimney connection requires a minimum 6" round or 8x8" square flue with at least 15’ height. Draft should be maintained between -0.01” to -0.02” w.c. at the over-fire test port; barometric damper installation may be necessary depending on site conditions.

Ideal Applications

Well-suited for retrofit or new construction in single-family homes or smaller commercial spaces where direct-fired domestic hot water is needed and where chimney venting is already in place.

Warranty Information

• Heat Exchanger: Limited Lifetime Warranty
• Other Components: 3-Year Parts Warranty