A new communication protocol – why?

The traditional room thermostat’s on/off controller is inadequately effective in fulfilling the communications needs of modern home heating systems. Consider the following developments for example:

  • Modulating central heating appliances
    More and more appliance manufacturers are bringing modulating central heating systems onto the market (see the overview of heating appliances). These appliances offer better efficiency and reduced environmental effects, as well as increased comfort. However, in order to operate these appliances, a communication protocol between the appliance and the controller is required.
  • Central heating remote control
    Central heating remote controls also require a more advanced protocol. The remote control can be used to operate the appliance using the temperature controller in the living room.
  • Thermostat information readings
    The same communication channel can be used to read appliance settings and other data like error and malfunction codes.
  • Expansion possibility
    A fourth advantage of using a communication protocol is that in future, the functionality of the system can be expanded by reserving enough space within the protocol for future applications.

What is OpenTherm?

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.

Identifiying the products

OpenTherm products can be identified by the OpenTherm logo. The logo’s presence guarantees a minimum level of interaction between central heating appliance and room thermostat. The extent of interaction depends on the extra functions built in by the manufacturer. The logo can be found near the terminal clip of the central heating appliance and the room thermostat.

Further information?
The OpenTherm Association’s secretariat can provide more information on the OpenTherm communication standard and the compatible products.

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Communication standard

Thermostats operated with a traditional on/off controller can be exchanged easily, regardless of whether they are regular thermostats or clock controllers. The same applies for the compatibility of central heating appliances operated by on/off controllers. This provides a wider choice to the fitters when determining the components of a heating system.

Yet when manufacturers of heating systems apply extra functions, more sophisticated communication protocols are needed. The various products are then no longer necessarily interchangeable. In this case, products (i.e. a central heating appliance and a controller) can only operate together provided that they use the same manufacturer-specific protocol.

On the other hand, if manufacturers of both central heating appliances and controllers all maintain a common standard protocol, their respective products can easily operate together. Hence, opting for a standard protocol means opting for a larger market and more freedom of choice for all market participants.

Standards for heating controllers

OpenTherm is a multi point to point communication protocol for use in residential heating. Furthermore, OpenTherm requires a standard type of connection like in any modern installation practice, i.e. a 2-wire low voltage and polarity-free connection. In addition OpenTherm can also be used as a wireless protocol.

The communication protocol describes the way digital information is exchanged between central heating appliances and room thermostats. The way this protocol is implemented, and any extra functionality resulting from the use of OpenTherm, is determined entirely by manufacturers of central heating appliances and room thermostats. Product documentations should state which system functions are available for particular combinations of products. In any case, using OpenTherm guarantees a minimum level of compatibility.

Future expansion possibilities include connecting OpenTherm controllers to a home bus system (yet to be determined).