Thermostat Question

[Robert11]

Hello,

For all youi electrical wizards out there:

Have a gas fired, forced hot water heating system.

Has 2 zones, circulator pump on each, and each with the very, very, basic older Honeywell non-digital thermostat. The old type, with the bimetallic spring and the mercury capsule.

Want to replace it with one of the new digital Honeywell.

The wiring from the existing thermostat to the furnace electrical circulator control boxes is

2-wire. Pretty simple, basic system.

The wires are red and white. But, the white wire seems to go to the red screw on each of the thermostats. And, the red wire to the white screw.

I am calling it the red and white screw, as the wires that connects these screws built into the thermostat that go to the bimetallic spring and heat anticipator are led off of them with a red wire, and a white wire. No molded in labeling, unfortunately.

Question:

For a system like this, 24 V AC, is this red-white wiring arbitrary, or truly polarity sensative ?

Thanks, Bob

[bud--]

At your 2 wire thermostats it makes no difference at all.

By convention, red is the power source wire and white is the switched wire that turns on the heat.

Some electronic thermostats operate on a battery which is charged (low current) from the voltage across the thermostat contacts when the heat is off.

-- bud--

[HVACTECH2]

Yes it is. but the main problem may be the new thermostat. what model and brand did you buy?

[hvacrmedic]

With two wires the connections are arbitrary. Without a third wire to the stat you'll need one that is battery operated if you go digital.

[Robert11]

Hi,

Thanks all for help; appreciate it.

The new digital Honeywell Thermostat I purchased is:

Model: RTH5100B (non programmable) Runs on 2 AAA batteries internally.

Thanks, Bob