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New thermostat and wiring

Hi all, I was hoping for a little advice. I might be overthinking it but I'm not very handy and like to be super clear about what I'm looking for before calling contractors!

Right now we have a hot water system on a Lochinvar KHB110 boiler. There's two zones (house had an addition added in the 90s) with two very old school Honeywell mercury manual thermostats, one for the old radiator front part of the house and one for the hot water baseboards in the addition. We also have a Mitsubishi FH12 wall unit on the first floor running off a remote and a ducted Mitsubishi SVZ handler in the attic for the upstairs on a MHK2 Redlink Thermostat (upstairs hallway). Both of these are primarily for AC and shoulder season heat since the hot water system is super comfortable during the winter proper.

I would really like to install newer thermostats. I would like to get wifi enabled ones that are programmable (don't need 'smart learning') and work well with hot water systems, but a lot of the information out there is geared towards furnaces and newer HVAC systems which I think have different cycling needs than rads. My understanding is that Nest stats are particularly bad for hot water systems? Ideally what I would really like is to be able to have the system more integrated via one portal (either at the thermostat or via app). I'd really like to program at least the FH12 into the wall thermostat, maybe through RedLink, if that's possible?

Complicating this is that both the existing manual thermostats are on two-wire wiring. The older thermostat is on EXTREMELY old wiring that has cloth wrapping and I'm super hesitant to touch it myself. I'd also like to move the thermostat for the addition to the next wall over because the placement is really awkward, so either way I need to have someone run new wires, I think.

General questions:
-Best wifi/newer thermostats for boiler systems? Should I go ahead and buy them or tell a plumber what I want and have him order?
-Who runs new thermostat wire? I need to have an electrician over for some other items anyway but I would think they wouldn't want to touch the boiler? Would I need an electrician to run wire and then have a plumber do the boiler and thermostat hook ups? I also have other plumbing work to be done (add TRVs for the upstairs rads and some bathroom work) so it's more figuring out order of operations.
-Is it possible to integrate the Mitsubishi units into the same system that operates the boiler?

Sorry for the super long post but I know trades guys are super busy in my area and I hate to call people and waste their time with a dozen dumb questions.


  • Jamie Hall
    Jamie Hall Member Posts: 23,318
    There are many many different digital thermostats out there, and a number which have wifi. Of that sort I like Ecobees. Any such unit will need new wiring -- including a common connection. But that shouldn't be that difficult.

    On another note: when you take the mercury Honeywells off the wall, please send me a PM and we can arrange for you to ship them to me. They are by far the most reliable thermostats out there and honestly I could use a couple more.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    Honeywell VisionPro thermostats use red link-WiFi technology, with remote sensors. The base units can be in the boiler room, with a 2 wire connection to the remote sensor.
    Still, running new wires, with more conductors, would be a good idea,—NBC