CGI-3 - 42,000 BTU Output Cast Iron Boiler, Spark Ignition - Series 4 (Natural Gas)

Weil-McLain CGI-3 Series 2 – Cast Iron Gas-Fired Water Boiler

The Weil-McLain CGI-3 Series 2 is a high-efficiency, atmospheric gas-fired water boiler designed for closed-loop hydronic systems. Manufactured with cast iron sections and built-in safety controls, this model is suited for residential and light commercial heating applications requiring a reliable, mid-efficiency boiler solution.

Rated at 42,000 BTU/hr DOE heating capacity, the CGI-3 offers dependable performance with an 84% AFUE. The unit supports natural gas operation with the option for field conversion to LP (propane) using a factory kit. Its compact profile, built-in low water cut-off, and spark ignition system simplify integration into tight mechanical spaces while maintaining serviceability.

Key Product Features

• Heat Exchanger: Cast iron sectional design for thermal mass retention and durability
• Combustion: Natural draft with intermittent electronic spark ignition
• Safety: Integrated low water cut-off control and pressure relief valve
• Venting: Chimney-vented; rear flue outlet with draft hood
• Fuel: Natural gas standard; convertible to LP

Technical Specifications

• Model Number: CGI-3 Series 2
• DOE Heating Capacity: 42,000 BTU/hr
• Net I=B=R Rating: 36,000 BTU/hr
• AFUE: 84%
• Input: 50,000 BTU/hr
• Ignition: Intermittent electronic (spark)
• Water Connection: 1-1/4" NPT
• Gas Connection: 1/2" NPT
• Relief Valve: 30 PSI included

Installation Notes

Installation should be performed by licensed HVAC or plumbing professionals. Combustion air, venting configuration, and zone piping must conform to local codes and Weil-McLain installation guidelines. Unit ships fully assembled for standing pilot-to-electronic conversion with minimal field setup. Clearance requirements and combustion air provisions should be reviewed prior to installation in confined mechanical rooms.

Contractor Applications

• System Type: Closed loop hydronic heating (baseboard, panel radiators, or radiant)
• Installation Environment: Indoor, non-condensing, chimney-vented locations
• Mounting: Floor-standing unit with leveling legs
• Service Access: Front access to gas valve, ignition module, and safety controls