Ultra 155 Series High Efficiency Natural Gas Boiler, 155,000 BTU

Weil-McLain Ultra 155 High-Efficiency Condensing Boiler – Model 383500735

The Weil-McLain Ultra 155 is a wall-mounted, condensing boiler engineered for hydronic heating systems in residential and light commercial applications. Designed for performance and efficiency, this unit features a cast aluminum monobloc heat exchanger and advanced combustion controls for reliable, low-emission operation.

Operating at up to 94% AFUE, the Ultra 155 meets or exceeds the efficiency requirements for ENERGY STAR® certification and supports compliance with local energy codes and rebate programs. It is suitable for use in systems requiring either natural gas or propane, and it supports modulation to closely match heating loads.

Core Features

• Heat Exchanger: Cast aluminum design offers high thermal conductivity, corrosion resistance, and an extended service life when used with properly treated water.
• Modulation Range: 5:1 turndown provides stable operation under varying demand, reducing short cycling and improving overall system efficiency.
• Burner Assembly: Stainless steel premix burner with Venturi gas-air mixing system supports clean, quiet combustion and low NOx output.
• Outdoor Reset Control: Built-in functionality adjusts boiler water temperature based on outdoor conditions, optimizing comfort and energy use.
• Integrated Control Platform: User-configurable menu with diagnostics and display; supports multi-zone control, DHW priority, and system pump management.

Technical Specifications

• Model Number: 383500735
• Input: 155,000 BTU/hr
• Net I=B=R Rating: 123,000 BTU/hr
• AFUE: 94%
• Fuel: Natural Gas or LP (field convertible)
• Vent Size: 3” (PVC, CPVC, or polypropylene approved)
• Max Vent Length: Up to 100 ft (varies by venting material and configuration)
• Water Connections: 1" NPT
• Gas Connection: 1/2" NPT
• Dimensions (H x W x D): 43.06" x 22.81" x 19.94"

Installation Considerations

This unit is intended for installation by licensed professionals only. Proper venting configuration, combustion setup, condensate management, and hydronic circuit design are critical to ensure safe and efficient operation. A full range of accessories—including system circulators, low-loss headers, and zone controllers—is available for integration with the Ultra series.

The control system supports direct pump control and integration with external indirect water heaters using DHW priority. System commissioning tools and onboard diagnostics assist in setup and long-term serviceability.

Design & Environmental Performance

• Low NOx Certified: Meets applicable air quality standards (<20 ppm NOx).
• Quiet Performance: Variable-speed combustion fan and burner design minimize operational sound levels in occupied spaces.
• Built-In Condensate Trap: Facilitates safe and code-compliant condensate drainage.
• Warranty: 15-year limited on heat exchanger (residential use); 2-year parts warranty.

Summary

The Weil-McLain Ultra 155 (383500735) is a robust, high-efficiency solution for hydronic heating professionals seeking a compact, condensing boiler for applications requiring up to 155 MBH input. It delivers consistent performance, flexible fuel compatibility, and advanced control integration, all within a space-saving wall-mounted format. Ideal for projects where efficiency, reliability, and long-term serviceability are required.