On 9/10/2011 1:58 PM, Selk Perkner wrote:
I have an older Weil Mclain gas steam boiler for the radiators in my
house. If the electricity goes out, it won't run -- I believe it needs
electricity to operate the gas valve, and the thermostat is also wired
into a circuit.

Should electricity go out to the house during the winter, I could
certainly get by for a few days with flashlights and coolers as long as
there is heat. I have instructions for running the boiler manually, and
could connect a battery operated thermostat, but would prefer to run it
on a backup electrical connection if possible so I don't have to babysit
it in the dark.

There is a single electical conduit running into the boiler which is
connected to a box with an on-off switch above the boiler, as well as a
line running from the thermostat.

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?

Is this just a quick project in the event of a major winter outage
(assuming I buy the parts ahead of time) or should I get the guy who
does the annual inspection do the work? I've done plenty of basic
wiring like running cable for new outlets and lights and switches, so
I'm not intimidated by basic stuff, but also know better than to mess
with stuff beyond my pay grade.

First, the thermostat doesn't use a separate power supply, it gets
whatever electricity it needs, through the boiler power supply. The type
of system you have probably requires very little current, but not
knowing the actual components involved, I couldn't tell if you could
back it up with a low voltage power source. The easiest way would be to
Install a switch in the 120 volt circuit that feeds the boiler, in
conjunction with a male plug wired to the switch. With the switch in one
position, the boiler would get it's power from the utility company
circuit. With the switch in the other position, the boiler would get
it's power from an alternate source that would be connected to the male
plug. You could use a very small generator, like 1000 watts, or even use
a battery backup pack, that delivers 120 volts AC.