Hello. I am trying to replace old Lux thermostat (similar to Lux TX500E) with new Honeywell RTH9580 model. Here's my situation:
- Old (1950s) gas floor furnace.
- We have NO air conditioning, and no fan - only the gas furnace.
- We have only 2 wires: red and white. These were connected to the Lux on the W (white wire) and RH (red wire) terminals.
- The new thermostat requires a third C wire which we do not have.
- Honeywell's info. Says that if no C wire, this model will not work.

I watched a video which showed how to create a C wire by modifying an AC power adapter/transformer with plug: https://www.youtube.com/watch?v=8a_f2_iAW1U

a. Is this safe to do (modified adapter)?
b. I would rather hardwire, instead of using adapter; is it safe to connect, instead, to a house wall outlet (through wall to the other side of wall/different room), and would this work correctly?
c. Optimally, if somehow possible, I would like to use only the two existing wires make this thermostat work, with all features operational, including Wi-Fi.

Please let me know if you need more information to answer, and thank you SO much for any help.

Happy Holidays!

That is a low voltage connection. Using house voltage will blow the thermostat. Find another compatible model or run another thermostat wire.