The type of HVAC systems that a Honeywell digital thermostat is compatible with varies with the type of thermostat. The Honeywell Wi-Fi Smart Thermostat is compatible with all 24-volt HVAC systems, for example, while the Digital Non-Programmable Line Volt Thermostat does not work with fan-forced heaters.
Honeywell produces a wide range of digital thermostats, as of 2015, including programmable, non-programmable and Wi-Fi Smart thermostats. The programmable thermostats are available in a range of models, such as 7-day, 5/2-day and 1-week. The 7-day models offer the most options, as they can be programmed separately for every day of the week, while the 5/2-day has an option for separate week and weekend programs.
The Honeywell Lyric thermostat is a programmable smart thermostat that connects to the home's Wi-Fi network and can be controlled remotely via a smartphone app. The thermostat uses a technique known as geo-fencing to determine the owner's location through a smartphone, which allows it to save energy while the owner is away and turn the system on when it detects that the smartphone is on the way home. The Lyric thermostat works with the majority of heating, cooling and heat pump systems, but it is not compatible with electric baseboard heaters over 110 volts.