A line voltage thermostat heat only is a type of thermostat that is used to control the temperature of a space or area. It is connected directly to the power line, and is used to regulate the temperature of a space by turning the heating system on and off. This type of thermostat is ideal for controlling the temperature of a single room or area, as it does not require a separate power source. It is also very reliable and easy to install. The thermostat works by sensing the temperature of the space and then sending a signal to the heating system to turn on or off depending on the desired temperature. This type of thermostat is often used in homes and businesses, as it is an effective and efficient way to control the temperature of a space.