On Sunday, March 12, 2017 at 3:01:48 PM UTC-4, wrote:
On Sun, 12 Mar 2017 09:55:05 -0700 (PDT), trader_4
wrote:

As would an Interlockit on the panel and inlet. Looks like
the same or less work than your switch/inlet solution for
just the furnace.

Load management is the problem when you are feeding the main panel.
You may find that there is just too much on the 2 or 3 circuits you
want to enable.

Being able to manage the loads from the panel is the beauty of
the whole thing. You could have some situation where there are
too many loads on one circuit, but I think that's rare. In my
case I had:

A freezer on one circuit
A fridge on another
Water heater power vent on another
Furnace on another
Lights/receptacles on a whole bunch of breakers, I just
turned on the ones for the lights/receptacles of interest.
I could have probably turned them all on, because there just
isn't that much there, especially with CFL, LED lights etc.
and with appliances only being used one at a time anyway, etc.