Honeywell Thermostat Question

5 Replies

Hello all,

I'm closing on my second property tomorrow (woo!).  I got a head start on a few things, and I bought a couple of 7 day programmable thermostats; they are Honeywell RTH2510B thermostats.  The side of the box mentions some heating and cooling systems it is compatible with.  All I have is a boiler, there is no central AC or anything like that.  One of the items the box states is a 750mv heating system.  I don't know if my heating system is 750mv or 24v.  Should I be concerned that I might fry this new thermostat if it is setup for 750mv but I have a 24v system?  Or should I assume I probably have a 24v system, and that the box is simply stating that the thermostat will also work with low voltage 750mv systems?

Sorry if that was confusing!  Thank you for any advice.

Hey Mark,

You’re good to go with that t-stat. Your system is 24 volt, heat only and runs off two wires. Let me know if you have any more questions.

Good luck!

Can’t answer that question for you but Congrats on the purchase!

@Robert Stark thanks for your help!  I thought I was most likely dealing with a 24v system.  I'll let you know if I run into anything else!

@Rod Hanks thank you!  It's my second house, but it'll the the first for me, my fiance, and her 5 year old son.  We're really excited!  We should be living mortgage free once we fill the other unit.

@Mark Smith It’s very unlikely that your system is a 750mv system. In all of the years that I have been doing HVAC work I can count on one hand the number of these systems I have come across. Millivolt (MV) systems are designated as such because they operate off of a very low voltage that is generated by a standing pilot light on a millivolt generator. These systems are dinosaurs and most have gone by the wayside long ago. Standing pilot systems are a thing of the past because the energy codes have done away with those and the majority of standing pilot systems are 24 volt systems. You stand a better chance of becoming a millionaire playing the lottery than finding a millivolt system.

@Tom W. , thank you for the insight.  My concern was that since the packaging my new thermostat was in stated 750mv on it, the thermostat would only work with a 750mv system and not a 24v system.  But from what Robert said above it sounds like I'm ok.

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