OpenTherm is a non-manufacturer-dependent system of communication between modulating HVAC heating appliances and room thermostats. It consists of a communication protocol and an interface specification. OpenTherm is a futuristic technology combining simple installation procedure with high functionality and future expansion possibilities. The OpenTherm communication protocol is primarily designed to control modulating heating appliances. As stated above, the protocol offers expansion possibilities which enable the manufacturer to build extra functions into their control devices or appliances as well as the basic function which is compulsory for all OpenTherm implementations. As such they can distinguish themselves from other suppliers and increase the freedom of choice for installers and consumers.