On Thu, 02 Feb 2012 17:16:11 -0600, wrote:

On 2 Feb 2012 15:08:43 -0500, (David Combs) wrote:

Here's what I want to do.

I've got steam/boiler heater, runs on gas, the only electricty
needed is to run the (solenoid?) thermostat, basically.

By "thermostat", do you mean thermostatically controlled valve?

That, and the thermostat, are in the same circuit and would be powered
by the transformer which is powered by the AC.

And the ignitor also. It's not enough to turn on the gas, you have to
light it too.

It's powered via a cable (covered in flexible metal tubing)
that connects into the wall 110-AC line.

What I want to do is get that changed from that direct connection
to the wall, to instead end in a grounded male plug.

This solenoid is most likely operated by a transformer with a secondary
voltage of around 24 volts.

Working on low voltage wiring is easy to do and should not need to
follow a lot of codes. Therefore, the simple solution is to not touch
the AC supply voltage at all. Instead, buy an extra transformer to be
powered from the generator. Install a DPDT (Double pole double throw)
switch in a box, and connect this to secondary of both transformers.
When the switch is flipped in one direction, the furnace will run the
transformer from the power line. When flipped the other way, it will
run from the generator. Label the switch so you know which way to flip
the switch.

You can buy a switch like this at Radio Shack. You can also buy small
aluminum boxes there to install it after drilling some holes in the box
for the switch and the wires. A DPDT switch has 6 terminals on the
back. The 2 middle ones go to the 2 wires going to the furnace. The 2
terminals on the left go to the transformer from the generator, the two
on the right go to the 2 wires from the line powered transformer.

Find a buddy who plays around with electronics to help if you need help.
There are ham radio guys and electronics experimenters all over the
country. Maybe the Radio Shack clerk knows of someone, or call a few
local TV repair shops.

Be sure to buy a transformer MADE for your furnace. Call a furnace
repair shop.

My first month in my 4-year old house, the AC failed, because the
furnace transformer failed. I went to a heating supply house and
since the transformer was part of the furnace control panel, his
reflex was to sell me a new control panel, for 400 dollars (in 1983)

I whined and he sold me a 24 volt transformer for maybe 30 dollars**,.
AFAIK all that is necessary is that it be 24 volts and big enough, to
power the furnace controls and the AC controls. Since the AC
compressor is on a separate cirucit, and the furnace air circulation
fan are on separate cirucits from the 24 volt control circuit, the
transformer doesn't have to be that big. Are you sure it has to be
made for the furnace? In my case it was a generic 24 volt
transformer, and I probably could have gotten it for less than the 20
or 30 dollars I paid at Radio Shack if they had one big enough, that
is, not a wall wart, not universal, and enough amps.


**I'm still using the same transformer 28 years later. It was too big
to fit where the original transformer was, so I mounted it on a
shelf/panel inside the furnace, though it could be mounted outside the
furnace too.

Problem solved!