Weil-McLain CGi Series 5 Gas Boiler 381359364 Cast Iron, Induced Draft, 84% AFUE
The Weil-McLain CGi Series 5 (Model 381-359-364) is a premium cast-iron, gas-fired hot-water boiler engineered for long-lasting comfort and efficiency. Designed for both residential and light commercial installations, this unit offers induced-draft performance, an 84% AFUE efficiency rating, and a durable cast-iron heat exchanger that ensures reliable operation for decades.
This CGi model includes Unity-CI text-based controls, a built-in low water cutoff, and a fully insulated jacket for improved thermal performance. With flexible venting, quiet operation, and proven reliability from Weil-McLain — North America’s most trusted boiler manufacturer — this system is an excellent choice for hydronic heating systems.
Features
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84% AFUE Efficiency for dependable heating performance.
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Unity-CI electronic control with digital text display for simple setup & diagnostics.
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Induced-draft design — improves venting reliability and system stability.
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Integrated low-water cutoff system for added safety.
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Heavy-duty cast-iron heat exchanger designed for long service life.
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Flexible venting: natural draft or direct exhaust options.
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Compatible with ECO-HP heat pump systems (Weil-McLain hybrid-ready).
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Quiet operation with stainless-steel burners.
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Tested for 50 PSI working pressure (CSA certified).
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Made in the USA heat exchanger.
What Our Experts Think
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Trusted cast‑iron performance: The Weil‑McLain CGi Series 5 Gas Boiler (Model 381359364) delivers durable, corrosion‑resistant cast‑iron heating with stable, steady output — ideal for space‑heating in homes or small commercial applications.
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Reliable induced draft design: The induced‑draft system improves combustion efficiency and airflow control, enhancing performance over older atmospheric units.
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Efficient operation: 84% AFUE provides respectable fuel savings and consistent warmth compared with older conventional boilers.
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Service‑friendly: Well‑engineered with accessible components, making routine maintenance and technician tuning straightforward.
Product Q&A
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What type of boiler is this?
A cast‑iron, natural gas‑fired hydronic boiler that generates hot water for baseboard, radiator, or radiant systems.
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What does 84% AFUE mean?
It means 84% of the fuel’s energy is converted into usable heat — the rest is lost through exhaust. This efficiency is typical for traditional induced‑draft designs.
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Where is this best used?
Ideal for single‑family homes, duplexes, or small commercial spaces where dependable, straightforward heating is desired.
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Does it require special venting?
Yes — induced‑draft boilers require proper venting (typically mechanical/vent fan and flue) per local codes and manufacturer specifications.
Maintenance Tips
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Annual professional service: Have a licensed HVAC technician inspect the burner, heat exchanger, combustion performance, and controls each year before the heating season.
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Monitor system pressure: Keep boiler pressure within manufacturer‑recommended ranges and check expansion tank functionality.
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Bleed air from circuits: Release trapped air in radiators or baseboards to ensure even heat distribution.
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Check venting and intake: Ensure vents, flue, and air intake remain clear of debris for safe combustion airflow.
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Inspect for leaks: Periodically check valves, fittings, and pipe connections for signs of water or gas leakage.
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Flush periodically: Sediment and scale may accumulate over time — periodic flushing helps maintain efficiency and prolongs component life
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