Honeywell Lyric Thermostat High Voltage Hack | Installation [High Voltage Conversion]

WARNING: THE FOLLOWING CONTENT IS FOR INFORMATIONAL PURPOSES ONLY

I am a licensed electrician that specializes in commercial building automation, lighting controls, fire alarm and security systems. I enjoy my work and these type of gadgets intrigue me.

My Home:

I live in a townhouse style of condo which has 3 thermostats that controls a local 240v unit heater. It's about 1,100 sqft and was built in the 80's.

My Problem:

Programmable line voltage thermostats are expensive and "smart" thermostats do not exist.

WARNING: THE FOLLOWING CONTENT IS FOR INFORMATIONAL PURPOSES ONLY

My Solution:

Parts:

Aube 240v Relay (RC840T-240) - integrated 24v transformer (C, W, R)

Wiremold 2G Box (BW32)

2G Blank Cover

Honeywell Lyric Thermostat

18” 18awg wire

Tools:

Screwdriver

Tweaker Screwdriver
Wire Strippers

Volt Meter

Lyric thermostat work with my system?

Will the Lyric thermostat work with my system?

The Lyric thermostat is designed to work on most low voltage heating and cooling systems, at 24 Volts. Gas and oil furnaces, heat pumps, and hot water systems are examples of these low voltage systems. The thermostat can also support multi stage systems with more than one stage of heating and cooling.
The Lyric thermostat does not work for 110V or higher line voltage systems, such as electric baseboard heaters. Thick black, red or white wires connected with wire nuts running to your existing thermostat will typically mean you have a high voltage system.

How do I replace a line voltage thermostat with a 24-volt one?

Its not as easy as it sounds. It can be done but there is no prepackaged kit that I know of because how to do it depends on your system. Some questions that have to be answered before you start a conversion: Are you using a heating only baseboard/fancoil/radiant/etc? Is this controlling a hot/cold water pipe change over system, or is it a 4 pipe system? Are you controlling two completely different pieces of equipment during cool/heat modes, are both those devices active the whole year or is one off? What about separate fan controller (see bottom)? Is it 120volts or 240/208 volts? How many AMPs? You must know these answers before you begin. Since I can't go over what to do in all situations I will start with the basics.

There are two fundamental kinds of line voltage thermostats, switches (the most common) and rheostats (or volt/amp variable controllers).