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My parents' house has a two-zone, in-floor hot water heating system, currently controlled by two separate Honeywell Chronotherm III thermostats. One of the thermostats is non-functional as the wires were cut somewhere between the garage (where the heating system is) and the thermostat.

Since the wires are cut, I'm thinking I'd like to install a wireless system like the FocusPro. However, at the moment, I'm trying to assess the system remotely (we don't live in the same area) and am trying to figure out if this is doable.

The first thing I'm not really sure of: given this is circulating water for radiant heat, what type of HVAC is this?...is it a furnace? heat pump? water circulator? I have a few photos taken of what I think might be the controllers that connect to the thermostats, and what I think is the hot water heater system.

I'll have physical access to the system next week, so I'll be able to look more closely at the units etc. But on the face of it: is there any reason why a system like the FocusPro with the equipment interface module couldn't replace these thermostats? Or, is there perhaps a better option? Thanks!

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This looks like an old, typical 80% efficient gas boiler, non-condensing. And forget HVAC, it's just H. Before you get all fancy with thermostat control, remember that in-floor heating systems typically take many hours to respond to changes in thermostat settings, so nighttime setback might not be useful, depending on the particulars.

My in-floor circulating water heat on my first floor (wood construction) takes 2 hours to go up 1 degree F, and an additional hour for each additional degree. If I lower the thermostat, room temperature drops half a degree per hour. (This is on a typical winter day in New Hampshire.) Therefore a 5-degree setback at night would take 10 hours (does anyone sleep that long?) and getting the house back up to temperature after the setback would take 6 hours. My finished basement, where the floor is concrete, takes 8 hours for the first degree of temperature rise. The bottom line for me is to set the thermostat at a steady temperature at the start of heating season and just leave it alone until spring.

If the wireless thermostat can interface with a plain vanilla 24 VAC zone controller, it should work fine. But I'd rather diagnose and repair the thermostat wire than get fancy with wireless.

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  • Good points. This is in Northern California, so the temperature control needed is probably not near what you're dealing with in New Hampshire! I think the Chronotherms learn when they need to turn on in order to hit the target temp, and it definitely takes some time, but IIRC, maybe just an hour or two to get warm enough to take the edge off. Again, that's more a function of the warmer winter we have.
    – Jeff
    Nov 13, 2022 at 21:38

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