When we moved into our house it had the standard rotary/mercury thermostat controlling an oil furnace. Unless you are a paranoid heat-miser, these old rotary units are highly inefficient and are typically the cause of your high heating bill, second to your drafty doors and windows. From past experience, I decided to replace the old unit with a digital programmable thermostat.

Typically we keep the thermostat set to 62 degrees overnight and at 65 during the day, starting 15 minutes before I wake up. Typically when I get home from work in the evening, I will manually increase the temperature to 68 until it resets back to 62 at 11PM.

Even with the programmable thermostat, there have been many times where I’ve been in bed and ended up being too hot or too cold. If I go to bed early, it’s pointless to keep heating the house until the programmed 11PM temperature drop.

Wanting even better climate control beyond my existing programmable unit, I decided to install a Z-Wave enabled Honeywell thermostat. It is important to note that this thermostat requires 24V AC via the standard “C” wire, found on most HVAC units. My particular system had only 2 wires running to the thermostat without the “C” wire. This would require new wire to be pulled and the installation of an external transformer.

Without having a “C” wire connection on my furnace, I had to install an external 24V AC step-down transformer. This appears to be a common add-on item for HVAC systems and was readily available from Lowe’s for $30. The transformer also included an ingenious junction box mounting plate, making installation clean and easy. Once I had the transformer installed, I had to run new wire to the thermostat. I was very fortunate that I had a short cable run as was able to snake a new 5 conductor thermostat wire using the existing 2 conductor wiring.

After the wires were terminated, thermostat mounted and power switched back on, the Honeywell unit lit up and was ready to be programmed. Initial configuration was very simple, although the manual was needed to configure it for heat-only, fan setup, and z-wave communications. Initially I was under the impression that this thermostat was not programmable, but judging by known feature set and price, this didn’t seem right at all. Reading the manual revealed that scheduling is disabled by default.

Adding the Honeywell thermostat to the hub software was uneventful and worked immediately. While I don’t plan on using the hub software to run a schedule, I plan to use it to remotely control the thermostat, particularly when I’m away from home.

Project notes:

  • As mentioned he Honeywell unit I’ve documented requires a 24V AC “C” wire. If you already have the “C” wire, installation should be fairly easy. With my technical ability I was easily able to add the “C” wire capability, but I highly recommend contracting an HVAC professional to assist with your installation.
  • READ THE MANUAL!!! Many of the programming and configuration items are hidden in a numerically coded menus which are only accessible by holding down unmarked keys.
  • If you have to replace your existing thermostat wiring, use the appropriate cable. The individual conductors are color coded. Keep with the standards, you’ll thank yourself down the road.