Honeywell VS8421D1104 Millivolt Gas Valve for Vent-Free Heating Appliances
Honeywell · Valves & Process Control
Description The 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. Technical Specifications Condition New/Never Used Surplus Brand Honeywell Category HVAC Controls Part Number VS8421D1104 Subcategory Millivolt Gas Valve Valve Type Combination millivolt safety gas control valve Operation Voltage Millivolt self-generating system (thermopile) Fuel Types Natural Gas / LP (Propane) Main Gas Connection 3/8″ NPT thread (typical for series) Pilot Gas Connection 7/16-24 UNS (typical) Regulator Setting (approx.) NAT: ~3–5 in W.C.; LP: ~8–12 in W.C. Maximum Capacity ~60,000 BTU/h (1-inch pressure drop, straight-through) Ambient Temperature Range ~0 °F to +175 °F (–18 °C to +79 °C) (series typical) Knob Positions OFF / PILOT / ON Safety Features Pilot flame detection, automatic shut-off Compatibility Replacement for VS8421 series valves Weight (approx.) ~2 lb Information About VS8421D1104 The 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. Key Features: Millivolt Operation: Functions using self-powered thermopile/thermocouple pilot circuit; no external 24 V supply needed. Manual Control Knob: Positions OFF / PILOT / ON for safe startup, pilot ignition and main burner operation. Adjustable Pressure Regulation: Factory-set with field adjustment: for natural gas ~3–5 in W.C., for LP ~8–12 in W.C. High Capacity Flow: Rated for up to ~60,000 BTU/h in straight-through application. Convertible Fuel Types: While set for a specific fuel, many valves in the series support both natural gas and LP with appropriate conversion options. Compact Design for Vent-Free Use: Optimised for vent-free fireplace and heater applications, with valve body sized for decorative equipment. Standard Connections: Main gas inlet/outlet fitted with 3/8″ NPT thread (typical), pilot connection ~7/16-24 UNS. Safety Shut-off Functionality: Automatically cuts off gas flow if the pilot flame fails or the thermopile output drops below threshold. Legacy Compatibility: Suitable for retrofits and replacements in systems originally using VS8421 series valves. The VS8421D1104 delivers the reliability and precise control required for safe, efficient millivolt-controlled vent-free heating appliance applications.
Brand: Honeywell · Category: Valves & Process Control
Key features
- Millivolt Operation: Functions using self-powered thermopile/thermocouple pilot circuit; no external 24 V supply needed.
- Manual Control Knob: Positions OFF / PILOT / ON for safe startup, pilot ignition and main burner operation.
- Adjustable Pressure Regulation: Factory-set with field adjustment: for natural gas ~3–5 in W.C., for LP ~8–12 in W.C.
- High Capacity Flow: Rated for up to ~60,000 BTU/h in straight-through application.
- Convertible Fuel Types: While set for a specific fuel, many valves in the series support both natural gas and LP with appropriate conversion options.
- Compact Design for Vent-Free Use: Optimised for vent-free fireplace and heater applications, with valve body sized for decorative equipment.
- Standard Connections: Main gas inlet/outlet fitted with 3/8″ NPT thread (typical), pilot connection ~7/16-24 UNS.
- Safety Shut-off Functionality: Automatically cuts off gas flow if the pilot flame fails or the thermopile output drops below threshold.
- Legacy Compatibility: Suitable for retrofits and replacements in systems originally using VS8421 series valves.
Specifications
| Manufacturer part number | VS8421D1104 |
|---|---|
| Condition | New/Never Used Surplus |
| Brand | Honeywell |
| Category | HVAC Controls |
| Part Number | VS8421D1104 |
| Subcategory | Millivolt Gas Valve |
| Valve Type | Combination millivolt safety gas control valve |
| Operation Voltage | Millivolt self-generating system (thermopile) |
| Fuel Types | Natural Gas / LP (Propane) |
| Main Gas Connection | 3/8″ NPT thread (typical for series) |
| Pilot Gas Connection | 7/16-24 UNS (typical) |
| Regulator Setting (approx.) | NAT: ~3–5 in W.C.; LP: ~8–12 in W.C. |
| Maximum Capacity | ~60,000 BTU/h (1-inch pressure drop, straight-through) |
| Ambient Temperature Range | ~0 °F to +175 °F (–18 °C to +79 °C) (series typical) |
| Knob Positions | OFF / PILOT / ON |
| Safety Features | Pilot flame detection, automatic shut-off |
| Compatibility | Replacement for VS8421 series valves |
| Weight (approx.) | ~2 lb |
| Product type | Millivolt Gas Valve |
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