White-Rodgers 21V51U-843

White-Rodgers™ 21V51U-843 2-Stage Universal Variable Speed HSI Integrated Furnace Control Kit, 24 V, 0.45 A


Manufacturer part number:



Emerson Electric


White-Rodgers™ HSI Integrated Furnace Control Kit, 2-Stage, Universal, Variable Speed, 15-1/2 Inch Lead Length, 15-1/2 Inch Probe Length, 24 V, 0.45 A, Natural Gas/Liquid Propane, 17 sec Warm Up, 15 sec Prepurge, 1/4 Inch Spade Terminals and Molex Plugs, Retries: 2, 60 min Reset, 8 Inch H x 5-1/4 Inch W x 1-1/4 Inch D, Includes: Keyed Wire Harness and 21D64-2 Universal Nitride Ignitor
  • 120 VAC igniter output
  • 120 VAC 2-speed inducer output
  • 120 VAC humidifier output
  • 120 VAC electronic air cleaner output
  • AC gas valve output
  • 16-Pin variable speed circulator output
  • Fuse protection – 3 amp
  • Furnace status LED – tri-color (green, red and amber)
  • Cfm LED – (green)
  • Heat fan off delay (dipswitch selectable)
  • Fan on delay for cooling
  • Historical fault retrieval by pushbutton
  • YLO, Y, W, W2, R, G, C, O, BK/DS/ Dehum terminals
  • Pressure switch inputs and monitoring
  • Flash microprocessor with non-volatile memory
  • Flame current measurement points

Standard/Approvals: CSA Certified

Application: Residential and Commercial Heating Equipment

Products specifications
Attribute nameAttribute value
Amperage Rating0.45 A
Control Voltage24 V
Dimensions8 Inch H x 5-1/4 Inch W x 1-1/4 Inch D
Electrical Connection1/4 Spade Terminals and Molex Plugs
Gas TypeNatural Gas/Liquid Propane
Lead Length15-1/2 Inch
ManufacturerEmerson Electric
Prepurge Time15 sec
Probe Length15-1/2 Inch
Reset Time60 min
Type2-Stage, Universal, Variable Speed
Warm Up Time17 sec