You need a way to connect the furnace to an extension
cord. One of the
better ways is to install an "inlet" (a male plug that
mounts like an
outlet) at the furnace.

**I know you know this, and just mis-typed (double throw
switch)

An added double pole switch connects the furnace

CY: Actually, a double pole double throw switch would be
wise. So that the generator neutral doesn't get connected to
the house neutral.

to either normal wiring or the inlet.


An extension cord connects the
inlet to your emergency receptacles.

CY: Sounds good, cord to the inlet.


I like the interlock from RBM. You would have to make sure
the loads you
want are balanced on both legs of the panel. Check the
cost and
convenience of different methods.

CY: The interlock sounds like a good idea, if the panel
supports it.