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The forced air furnace is propane and runs off the wall thermostat and uses the coach batteries.  The motoraide heater uses the engine coolant and there is a knob above it that turns to open and close the coolant valve for the amount of heat you want.  The switch over the driver's head controls the fan for the motoraide heater.  I am shocked at how well that heater works while on the road.  In less than a minute the coach is toasty.  Of course these coolant lines also feed the Atwood Marine water heater.  My water is piping hot at 190 degrees F. after a short time of driving.  I would recommend taking a look at all of these coolant lines and elbow fitting to be sure the are in good shape.  It is tedious but I just replaced all of them in my 1999 HD.  Peace of mind and no coolant smell in the coach.  I had to buy that special "Y" pipe the seperates the motoraide water heater from the motraide heater core.  You can still get it from Winnebago but it is a tricky part number to find.  I spent nearly an hour on the phone, but bought my shiny new pipe.  The old one had some corrosion and I suspected a possible leak.  Again, safety and peace of mind first.