Weil‑McLain EG‑40 – 125 MBH Cast‑Iron Gas Boiler, 84 % AFUE (Water/Steam, Tankless Opening)
The EG‑40 is a cast-iron sectional boiler with a 125 MBH input, delivering approximately 106 MBH net output in a water system (or 78 MBH for steam), and rated 84 % AFUE. It arrives knock-down for field assembly with a factory-feasible tankless coil port—ideal for installers planning tankless DHW integration
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???? Core Contractor Features
Rugged Cast-Iron Build
Boiler sections rated for 50 PSIG, include built-in air separator, and come insulated with a vent damper-enhanced jacket to lower standby losses
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Gas Ignition Assembly
Equipped with intermittent electronic ignition, stainless-steel burners, combination gas valve, and a draft hood configured horizontal-to-vertical to eliminate traditional bulky chimney hoods
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Servicing Accessibility
Includes easy-access controls, electrical junction box, spill switch, rollout thermal fuse, and plug-in wiring for servicing convenience
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Flexible DHW Integration
Built with a left-side opening for tankless-coil installation; piping for ½″ coil with easy access, supporting ~3 GPM at typical boiler temperatures
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Water Boiler Safeties
Comes standard with pressure-temperature gauge, 30 PSI ASME relief valve, high-limit control, and either integrated LWCO (for water versions) or universal control with diagnostic lights (if ordered with coil opening)
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???? Quick Specs Table
Item Specification
Input Rate 125 MBH
Net Output (Water) ≈ 106 MBH
Net Output (Steam) ≈ 78 MBH
AFUE 84 %
Pressure Rating 50 PSIG
Vent Type Horizontal-to-vertical draft hood, 6″ chimney
Ignition System Intermittent electronic
Dimensions (approx.) 33¾″ H; 21″ W; 19″ D
Weight ~505 lb
????️ Installation & Service Highlights
Combustion Efficiency: Includes automatic vent damper to reduce standby fuel usage and improve efficiency
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Service Efficiency: Front and top access panels, plus removable harness, reduce maintenance time.
Retrofit-Friendly: Knock-down sections fit through 30″ doorways; rear or side tankless coil installations supported.
Standard Venting Approach: Clearances and draft outlined in installation manual 550‑110‑639; guidance provided for chimney sizing and airflow.
???? Contractor Summary
The EG‑40 offers a solid cast-iron design with high AFUE for hydronic or steam applications. It’s built with serviceability and flexibility in mind—optional tankless coil, draft collar, and standard water-side controls. Its rugged construction and built-in efficiency features make it a strong choice for long-term heating projects in residential and light commercial installations.