Heating Thermostat Hookup Question


Hello:
Replacing a very, very old Honeywell thermostat with one of those new digital ones. Have a forced hot water system (no cooling).
It is a 2 wire system.
The wires coming up to the existing thermostat (a mechanical one with the mercury vial on a coil spring type) are not color coded.
Also, the screws where these wires connect to the old thermostat do Not have any molded-in labeling that I can see. May have worn off.
My question is:
Since these wires are "probably" coming from the secondary of a transformer, and operate a relay, can I safely assume, probably, that there is no polarity involved, and either can be hooked to either connector on the new thermostat that is for a 2 wire system ?
The only reason I can think of that this wouldn't be true is if this transformer secondary might have one leg grounded, but I doubt (but am not sure) that this is the case.
Any thoughts on ?
Thanks, Bob
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You've got a 24 volt series 80 thermostat, probably a Honeywell T87, you can replace it with any series 80 two wire thermostat. It doesn't matter which wire goes to R or W

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