That's a savings of $60 on heating per month, for five months. The laws of thermodynamics continue to be enforced regardless of bubble or not, so I think it quite impossible to save more than 10%. So you're averaging $600 or more to heat. Averaging...
I live in Wisconsin where I would be hard pressed to spend $300/month during the worst imaginable weather (and this is five months... the worst imaginable weather is .. January. Three months earlier or later isn't too bad, back to $100/mo or less). With the recent polar vortex event settled right over my house, maybe this will be a $400 month for me... maybe not.
I assume by "bay area" and spending $600/mo on heating you mean Prudhoe Bay on the north slope of Alaska?
They have a widget on the Nest store (https://widgets.nest.com/en/calculator/widget) that estimates energy savings. According to that, a $250/year savings is possible in SF with electric heating and a house over 2000 square feet. Though, the range they provide probably means:
a) It is a historically cold year for a prolonged period of time
b) You set your heat to 80F all the time
With gas heating, it looks almost impossible to save $250... unless you're heating an NBA arena.
