WINNOCTURN, now that is so straightforward that many will have a hard time getting their mind around the concept!
Actually pretty neat. The only downside I can see is not having the use of the upstairs emergency shut off switch as I assume you have this right above the furnace.
We do have a single circuit transfer switch that I installed at the power panel to power the furnace.
http://www.reliancecontrols.com/Prod...il.aspx?TF151W