Ducted/radiant-heated holding tanks

Pads are optional equipment as shown on page 112: (better look for the switches)

HEATED HOLDING TANKS
With the heated tankoption, a pad will be glued to the exterior bottom side of the holding tank. Heat
is supplied by 12-volt DC power through the heating element built into the pad. Approximately
6-amps of energy per pad is consumed and fused through the 12-volt power supply board. Switches
to turn heat pads on or off are located on an interior wall in or near the bathroom.
POWER TO HEATING PADS SHOULD BE TURNED OFF UNTIL:
1. Water is in the holding tank.
2. Temperature drops to 32° (0° C).
3. Motorhome is parked, setup and all attachments performed.
NOTE: Turn heat pads off when dumping and draining tanks.
An internal thermostat is built into components of the heat pad to assist in energy conservation.

Looks like Doug nailed it........duct AND pads
Owners Manual

Ducted radiant heat sound like what the first fella said. If you do have electric heating pads make sure they are one third full before turning them on. That's what I have been told and read myself several times. They will not operate correctly and could ruin them if operated empty.

Thank you both. Very much appreciated.

YES....

It means one duct coming from furnace discharge plenum goes into the enclosed underbelly area to provide heat to waste tank area. Warm air in the space helps keep tanks warm via radiant heat.

Ducted means they ran part of the furnace ducting over the holding tank area(usually the fresh tank. Radiant means they ran a 12 volt heat pad on the bottom of each holding tank. If you have exposed Holding tanks, look at the bottom of each tank and see if there is a flat pad with 2 wires glued to the bottom of each tank. There should be a 12 volt switch inside the bathroom area labeled Tank Heater. Usually lighted red in color. Doug