OpenTherm is a point-to-point communication system that connects condensing gas central heating boilers with ‘Smart’ room thermostats. The OpenTherm language sets the rules on how the boiler and the room thermostat communicate with each other.
When installed, an OpenTherm compatible boiler, such as the awesome Intergas ECO RF using OpenTherm compatible controls (we recommend Honeywell’s Lyric T6R) will control your boiler’s central heating water temperature and modulate the appliance to the correct temperature set point at all times.
Traditional basic ON/OFF heating controls (including Time, Proportional & Integral (TPI) controlled heating systems) have no affect on the boilers water temperature and this is always controlled by a fixed preset value (usually set at the boiler). This is not the most efficient way to run the boiler, especially during Spring & Autumn months when heating demand is less than in Winter months as it’ll be constantly clicking on and off rather than running at a steady lower temperature to match the demand.
How does OpenTherm work?
In the UK, the traditional way to control a central heating system is with a basic ON/OFF or TPI room thermostat. The room thermostat is set to a temperature and will switch the boiler ON and OFF; when the room temperature falls below the temperature set point, the thermostat switches the boiler ON and then when the room temperature goes above temperature set point, the thermostat turns the boiler OFF. The result of this is shown in the graph below.
From the graph above, you can see it shows that the set point of 19 degrees Celsius is not accurately controlled and the temperature in the room both ‘overshoots’ and ‘undershoots’ the required set temperature in the room. It does this because the thermostat isn’t smart in the way it operates (i.e. no temperature feedback to the boiler). This can feel uncomfortable and normally leads to occupants setting the thermostat higher than required. The frequency of the boiler turning on and off also increases wear and tear on the boiler itself and is an inefficient way to control it.
OpenTherm provides a much more precise control of the boiler, by continuously adjusting the boiler’s water temperature set point (Control Set point). OpenTherm always assumes that the room thermostat calculates the amount of heat required from the boiler and this is matched to the varying demand requirements. By setting the boiler’s water temperature to the correct temperature set point as it leaves the boiler, OpenTherm not only maintains the correct room temperature set point but also helps the boiler’s efficiency by running at lower flow temperatures for longer periods; this ensures more of the boilers heat exchanger is at condensing temperatures, which is the boilers most efficient point – therefore, saving you money on your gas bills, and helping doing your bit for the environment.
The OpenTherm thermostat graph above shows that once the temperature of the room nears its temperature set point, the boiler is told to reduce its output (Control Set point) to prevent the room temperature overshooting. Once the room sensor sees that the temperature set point has been achieved, it will tell the boiler to change its temperature set point to a lesser value, dependant on the feedback the room sensor is receiving.
This all sounds really interesting(!), but what are the benefits?!
- Increased efficiency of heating system = saving on your gas bills
- No need to configure – ‘plug and play’
- Reduced boiler start/stop occurrences = reduced wear and tear
- Extra functions – boiler fault codes can be displayed on the room thermostat
- Option for remote control and diagnostics (great if you’re a landlord with tenants that like to fiddle)
- Increased life of the boiler
If you’ve made it this far and you’re still awake – I applaud you!