In article ,
Selk Perkner wrote:

The thermostat is obviously a straightforward job, but is it a
straightforward job to switch the power at the on-off switch from the
regular house current to a backup source? How much capacity will this
backup need -- does it pretty much need to be a gas generator, or can I
get by with a battery backup of some sort?

you'd need to provide more info, ie model number and all those pesky rating
numbers, but as a guess you could do it with a battery, inverter and cutout
switch.

if you were going to use a generator to provide the electricity, it would be
easier to capture the waste heat instead of using your boiler