Oil-Fired Chimney Vent Water Boiler, 100MBHOP , 84% AFUE, Series 3

Williamson OWB-5-T-S3-W – Oil-Fired Water Boiler with Chimney Vent, 140 MBH Input

The Williamson OWB-5-T-S3-W is a high-output, oil-fired cast iron boiler engineered for water-based heating systems. With a rated input of 140,000 BTU/hr and an 84% AFUE, this model is designed for residential and light commercial applications requiring consistent, high-efficiency hydronic performance. This Series 3 unit features a traditional chimney vent configuration and a tankless coil for domestic hot water production.

Product Highlights

• Heat Exchanger: Cast iron sectional design ensures heat retention and longevity under continuous operation.
• Tankless Coil: Integral domestic water coil provides on-demand hot water without the need for a separate water heater.
• AFUE Rating: 84% (measured per DOE test procedure for oil-fired boilers)
• Vent Type: Natural draft chimney venting; suitable for lined or unlined masonry chimneys or approved B-vent.
• Combustion: Oil-fired with Beckett burner standard (Riello and Carlin options may be available depending on configuration)

Key Features

• DOE Heating Capacity: 126 MBH
• Net I=B=R Rating: 110 MBH (water)
• Flue Configuration: Rear flue outlet; may require barometric damper and draft testing
• Controls: Includes high-limit control, circulator relay, and low water cut-off for added protection
• Factory Assembly: Burner mounted and wired; tankless coil and controls pre-installed for faster setup

Installation and Application

The OWB-5 is intended for closed-loop hydronic systems and can serve baseboard, panel radiators, radiant systems, or indirect water heaters. Installation should be performed by a licensed HVAC or plumbing contractor to ensure compliance with local codes and to properly set combustion parameters. Clearances must be observed for service access and combustion air requirements.

Contractor Notes

• Boiler ships fully assembled (except flue pipe and oil line)
• Requires proper combustion air supply and draft control setup
• Tankless coil connection ¾" NPT – verify domestic flow rate requirements for application
• Oil supply line should be tested for vacuum and leaks after final connection

Warranty

• Heat Exchanger: Limited lifetime warranty (residential applications)
• Other Components: 1-year parts warranty

Summary

The Williamson OWB-5-T-S3-W is a workhorse oil-fired boiler for professionals requiring dependable performance in traditional chimney-vented applications. Its integrated domestic coil, cast iron construction, and service-ready layout make it a solid choice for retrofit or new construction jobs where durability and ease of service are priorities.