I replaced my old thermostat with a lyric. My doorbell transformed was unused and 16 V. I replaced that with a 24 and wired it directly to my lyric. Everything works great.

If I do an additional thermostat in a different zone can I just add more wire to that existing transformer? Will multiple devices on the 24v cause issues?


  • it should not, unless the transformer is pretty weak ... i would connect the 2nd thermostat and if there are problems, i'd install a second transformer
    – jsotola
    Commented Feb 26, 2018 at 19:13
  • I can't find a solid source for the electrical requirements for the thermostat, but from experience, there's no way that two will overload a typical 24VAC A/C transformer. You could probably run 50 thermostats off one.
    – JPhi1618
    Commented Feb 26, 2018 at 19:55

2 Answers 2


I have run multiple thermostats and even a 24v damper off a single transformer. Most thermostats are very low draw but to make sure look up the power requirements for each and add them together. Now compare that to the transformer wattage/ amperage. If less is needed from the 2 stats than the transformers rated output you are good to go. If the same or more than the transformers output you can get a larger single or another smaller transformer (usually cheaper) and have 1 for each stat.


Ratings matter. Every transformer has a VA rating. Every thermostat has a VA rating.

You know which transformer you bought, and the VA rating is important enough to be usually part of the name of the product.

You can compare the VA rating of the transformer to the VA draw of everything connected to the transformer.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.