{"product_id":"honeywell-vs8421d1104-millivolt-gas-valve-for-vent-free-heating-appliances","title":"Honeywell VS8421D1104 Millivolt Gas Valve for Vent-Free Heating Appliances","description":"\u003ch4\u003eDescription \u003c\/h4\u003e\n\u003cp data-end=\"396\" data-start=\"144\"\u003eThe Honeywell VS8421D1104 is a millivolt-operated gas control valve designed for vent-free fireplaces and space-heating units. It provides integrated safety shut-off, regulator adjustment and manual knob control (OFF\/PILOT\/ON) for reliable fuel-flow management.\u003c\/p\u003e\n\u003cp class=\"\" data-end=\"574\" data-start=\"284\"\u003e \u003c\/p\u003e\n\u003cp class=\"\" data-end=\"574\" data-start=\"284\"\u003e \u003c\/p\u003e\n\u003ch4\u003eTechnical Specifications \u003c\/h4\u003e\n\u003ctable style=\"width: 100%; height: 411.469px;\"\u003e\n\u003ctbody\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 19.5938px;\"\u003e\u003cstrong\u003eCondition\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 19.5938px;\"\u003eNew\/Never Used Surplus\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 19.5938px;\"\u003e\u003cstrong\u003eBrand\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 19.5938px;\"\u003eHoneywell\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 19.5938px;\"\u003e\u003cstrong\u003eCategory\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 19.5938px;\"\u003eHVAC Controls\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 19.5938px;\"\u003e\u003cstrong\u003ePart Number\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 19.5938px;\"\u003eVS8421D1104\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 19.5938px;\"\u003e\u003cstrong\u003eSubcategory\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 19.5938px;\"\u003eMillivolt Gas Valve\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 19.5938px;\"\u003e\u003cstrong\u003eValve Type\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 19.5938px;\"\u003eCombination millivolt safety gas control valve\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 19.5938px;\"\u003e\u003cstrong\u003eOperation Voltage\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 19.5938px;\"\u003eMillivolt self-generating system (thermopile)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 19.5938px;\"\u003e\u003cstrong\u003eFuel Types\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 19.5938px;\"\u003eNatural Gas \/ LP (Propane)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 19.5938px;\"\u003e\u003cstrong\u003eMain Gas Connection\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 19.5938px;\"\u003e3\/8″ NPT thread (typical for series)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 19.5938px;\"\u003e\u003cstrong\u003ePilot Gas Connection\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 19.5938px;\"\u003e7\/16-24 UNS (typical)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 39.1875px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 39.1875px;\"\u003e\u003cstrong\u003eRegulator Setting (approx.)\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 39.1875px;\"\u003eNAT: ~3–5 in W.C.; LP: ~8–12 in W.C.\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 39.1875px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 39.1875px;\"\u003e\u003cstrong\u003eMaximum Capacity\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 39.1875px;\"\u003e~60,000 BTU\/h (1-inch pressure drop, straight-through)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 39.1875px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 39.1875px;\"\u003e\u003cstrong\u003eAmbient Temperature Range\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 39.1875px;\"\u003e~0 °F to +175 °F (–18 °C to +79 °C) (series typical)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 19.5938px;\"\u003e\u003cstrong\u003eKnob Positions\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 19.5938px;\"\u003eOFF \/ PILOT \/ ON\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 19.5938px;\"\u003e\u003cstrong\u003eSafety Features\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 19.5938px;\"\u003ePilot flame detection, automatic shut-off\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 19.5938px;\"\u003e\u003cstrong\u003eCompatibility\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 19.5938px;\"\u003eReplacement for VS8421 series valves\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 33.8025%; height: 19.5938px;\"\u003e\u003cstrong\u003eWeight (approx.)\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"width: 62.8849%; height: 19.5938px;\"\u003e~2 lb \u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003cp\u003e \u003c\/p\u003e\n\u003cp\u003e \u003c\/p\u003e\n\u003ch4\u003eInformation About \u003cspan data-sheets-root=\"1\"\u003eVS8421D1104\u003c\/span\u003e\n\u003c\/h4\u003e\n\u003cp\u003eThe VS8421D1104 is part of Honeywell’s VS8421 series of millivolt gas valves, built for vent-free (unvented) decorative fireplaces and space-heaters. It functions using a thermopile\/thermocouple to generate the small millivolt signal required for operation, eliminating the need for separate 24 V control wiring. The valve incorporates regulator settings for natural gas and LP (propane) and is rated for a capacity of approximately 60,000 BTU\/h (with a 1-inch pressure drop straight-through configuration). It accepts a 3\/8” NPT main connection and includes multiple safety features for flame failure and fuel control. As part of Honeywell’s legacy valve family, it is compatible with installations requiring reliable millivolt gas valve operation.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eKey Features:\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eMillivolt Operation: Functions using self-powered thermopile\/thermocouple pilot circuit; no external 24 V supply needed.\u003c\/li\u003e\n\u003cli\u003eManual Control Knob: Positions OFF \/ PILOT \/ ON for safe startup, pilot ignition and main burner operation.\u003c\/li\u003e\n\u003cli\u003eAdjustable Pressure Regulation: Factory-set with field adjustment: for natural gas ~3–5 in W.C., for LP ~8–12 in W.C.\u003c\/li\u003e\n\u003cli\u003eHigh Capacity Flow: Rated for up to ~60,000 BTU\/h in straight-through application.\u003c\/li\u003e\n\u003cli\u003eConvertible Fuel Types: While set for a specific fuel, many valves in the series support both natural gas and LP with appropriate conversion options.\u003c\/li\u003e\n\u003cli\u003eCompact Design for Vent-Free Use: Optimised for vent-free fireplace and heater applications, with valve body sized for decorative equipment.\u003c\/li\u003e\n\u003cli\u003eStandard Connections: Main gas inlet\/outlet fitted with 3\/8″ NPT thread (typical), pilot connection ~7\/16-24 UNS.\u003c\/li\u003e\n\u003cli\u003eSafety Shut-off Functionality: Automatically cuts off gas flow if the pilot flame fails or the thermopile output drops below threshold.\u003c\/li\u003e\n\u003cli\u003eLegacy Compatibility: Suitable for retrofits and replacements in systems originally using VS8421 series valves.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eThe VS8421D1104 delivers the reliability and precise control required for safe, efficient millivolt-controlled vent-free heating appliance applications.\u003c\/p\u003e","brand":"Honeywell","offers":[{"title":"Default Title","offer_id":50777049596202,"sku":"VS8421D1104","price":685.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0800\/0392\/4266\/files\/s-l1600_78798f8c-0c8d-4648-9cd7-fc3a44144bb3.webp?v=1762278894","url":"https:\/\/iqelectro.com\/products\/honeywell-vs8421d1104-millivolt-gas-valve-for-vent-free-heating-appliances","provider":"IQElectro","version":"1.0","type":"link"}