New Thermostats

When we bought our house in 2001, it had an old Weil-McLain boiler with two heating zones – one for the main floor, and one for the basement family room. The boiler water temperature was kept at the “high limit” setting of 180°F, and each heating zone had a line-voltage thermostat wired directly to the zone’s circulator pump. This was a “non-standard” setup to say the least. Around 2003 or 2004, at the pinnacle of my DIY home-improvement kick, I converted to a more conventional system with transformers and low-voltage thermostats, installing a Honeywell “Chronotherm IV” programmable thermostat on the main floor and a manual mercury-switch thermostat in the basement. In 2006, we replaced the boiler and split the main floor into two zones: one for the living areas, and another for the bedrooms. I moved the Chronotherm into the bedroom, upgraded to a new touch-screen thermostat in the living room, and left the mercury thermostat in the basement, and that’s how things stood for almost 18 years. Now, I’m looking at upgrading to newer thermostats that we can access remotely and tie into a home automation system. For starters, I bought two Sinopé TH1400ZB heating thermostats to use for the basement and bedroom zones. To make a long story short, these thermostats require a common (C) wire, but inexplicably, when I rewired everything for low voltage back in 2003-2004, I only ran 2-conductor thermostat wire. So, I spent a good part of an afternoon last weekend pulling out the old basement zone wire and replacing it with 3-conductor wire. Today, I did the same thing with the bedroom zone wire, and the living room wiring is still TBD. I’m not sure what my thinking was back then, but I definitely wasn’t thinking that my rather short-sighted decision would create more work for me in the future. I probably thought that my (then) state-of-the-art power-stealing Chronotherm and battery-powered VisionPro thermostats would never need to be replaced, or that the eventual replacements would run on 2 wires. In any case, the moral of the story is: when wiring thermostats, always run a common wire, even if you think you don’t need one. 😀