Fossil Fuel Kit Used with Gas & Heat Pump Systems (Rheem Ruud)
Fossil Fuel Kits
• RXPF Fossil Fuel Kits are intended to be used where the heat
pump may provide heat at a lower cost than oil, natural gas or L.P. gas
within a certain outdoor temperature range. The kit permits the heat pump
to operate at temperatures (usually from 30
•F to 35
•F and above) where
the heat pump is most efficient. For the colder periods, the heating will be
provided by a standard furnace which has approximately the same efficiency
at all temperatures.
The RXPF Fossil Fuel Kits are for use with Rheem Heat Pumps and most
fossil-fueled warm air furnaces. They operate by turning the heat pump off
at a pre-determined outdoor temperature permitting the furnace to heat as
demanded by the wall thermostat. When the outdoor temperature warms
up, it will lock out the furnace and let the heat pump do the heating.
A plenum switch is employed that will, during heat pump defrost, turn the
furnace on as required to prevent cold drafts.
The set point of the kit is adjustable. The recommended set point should be
that temperature at which the heat pump will just provide 100% of the heating
When used with a recommended thermostat, the emergency heat feature
easily allows conversion to 100% fossil fuel heat should the heat pump fail,
for any reason. Also, the heat pump only switch on the kit allows 100% use
of the heat pump if for any reason the fossil fuel heat should fail (such as
component failure or lack of fossil fuel).
• Heat Pump Operation when Outdoor Air Temperature is above set point.
• Gas Furnace Operation when Outdoor Air Temperature is below set point.
• Blower Speed)
• Indoor Thermostat set to
• Outdoor Thermostat Set to
•, only the Heat Pump Operates.
• Indoor Thermostat Set to
•, only the Furnace Operates on 1st Stage.
• Defrost, Furnace cycles on when supply air temp. drops to 95
Off when supply air temp. reaches 110
•F. Blower runs in cooling speed.
Replaces Rheem, Ruud Weatherking Part Numbers:
Used in Rheem, Ruud Weatherking Equipment Models:
• II PLUS 2 LXE
Plenum Switch Assembly
Wiring Diagram Thermostat
Booklet Remote Heat Pump