Natural Gas Steam Boiler with Spark Ignition and Probe LWCO, 125,000 BTU

Williamson GSA‑125‑N‑IP‑S2‑W – 125 MBH Atmospheric Gas Steam Boiler (82% AFUE)

The GSA‑125 is a cast-iron, natural-gas-fired steam boiler with intermittent spark ignition and a built-in automatic vent damper. With a 125,000 BTU/hr input, 103,000 BTU/hr heating capacity, and net steam output of 77,000 BTU/hr, it delivers reliable steam for residential and light-commercial systems at 82% AFUE. Factory packaged with a pilot, draft hood, and probe low-water cut-off, it's ready for quick installation with minimal field assembly :contentReference[oaicite:1]{index=1}.

???? Core Technological Features Heat Exchanger: Cast-iron sections assembled with push nipples, tested to withstand steam pressure and thermal cycling 24hr.supply +4 ecomfort.com +4 acwholesalers.com +4 . Steam Output: Rated to handle ~321 sq ft of steam radiation, producing 77,000 BTU/hr of usable steam output williamson-thermoflo.com . Burner: Stainless steel intermittent spark ignition system ensures consistent light-off and efficient combustion. Vent and Damper: Equipped with automatic vent damper and standard chimney-draft hood to reduce standby losses goatlantic.com +11 williamson-thermoflo.com +11 24hr.supply +11 . Jacket and Access: Heavy-gauge insulated steel jacket with one-piece front access door for fast servicing afsupply.com +15 afsupply.com +15 acwholesalers.com +15 . ???? Installation & Service Practicalities Factory-Tested Assembly: Unit ships assembled with all draft, pilot, and low-water cutoff systems operational and ready for field gas hook-up acwholesalers.com +5 afsupply.com +5 afsupply.com +5 . Combustion Air: Requires proper chimney or Type B vent; vertical vent pipe recommended per manual specifications williamson-thermoflo.com +1 ecomfort.com +1 . Service-Friendly Layout: Internal components (ignition module, pilot assembly, control panel) accessed easily from the front. Clearances: Includes standard OSHA-compliant space for burner service and draft hood clearance per boiler manual afsupply.com +4 williamson-thermoflo.com +4 powerequipmentdirect.com +4 . ???? Performance Specifications Specification Value Input 125,000 BTU/hr Heating Capacity 103,000 BTU/hr (DOE) Net Steam Output 77,000 BTU/hr AFUE 82% Vent Collar 6″ diameter (chimney vented) Clearance One-piece front access for servicing Controls Intermittent spark, LWCO probe, damper Warranty 10-year heat exchanger, 1-year parts ✅ Contractor Summary The Williamson GSA‑125‑N‑IP‑S2‑W is a proven, field-assembled steam boiler offering moderate capacity for residential and light commercial systems. Its cast-iron durability, spark ignition, and sealed combustion package provide dependable performance while reducing service time. The boiler's simplicity and service accessibility make it an excellent candidate for retrofit jobs or projects requiring reliable, traditional steam heat.