Anyone buying or installing a new central heating boiler needs to be aware of a recent change in the law. Since April this year, it has been a legal requirement for all gas combi boilers (the most popular type sold in the UK) to have at least one of the four ‘Boiler Plus’ energy-saving features. The bad news is that there’s a lack of available or reliable information about which one of those four options might be best. The good news is that making the right choice can reduce a typical home’s heating bill – and in the real-life experience of Viessmann, the German heating systems manufacturer, that will be by as much as £40 to £100 per year.
The four types of Boiler Plus technology identified by the new rules, which are an addition to Part L of the Building Regulations, are flue gas heat recovery, smart thermostats with automation and optimisation, load compensation, and weather compensation. The new Boiler Plus regulations also state that gas boilers must be at least 92% efficient under the ErP (Energy related Products) rating system and must have boiler interlock (a safety fail-safe), plus time and temperature control.
According to a government consultation document, three of the four Boiler Plus features take anything from 11 to 14 years to pay back their cost of £50 to £460 through energy savings. But one feature, weather compensation, beats the others hands-down. In fact, real-life data gathered by Viessmann UK and scientific research by Salford University shows that weather compensation, which typically costs about £130, will pay back in less than four years. So if you find yourself wondering which Boiler Plus feature to select, there’s your answer.
Weather compensation achieves such significant energy savings because it uses a small sensor located on an outside wall of the building to inform the boiler controls what the outside temperature is. When the outside temperature changes, the boiler responds by increasing or decreasing the water temperature to the radiators to compensate. This is about 15% more energy efficient than a heating system which sets the temperature only according to a room thermostat. That’s because a room thermostat only takes effect after the inside of the building has become too hot or too cold, which causes a wasteful cycle: the room gets too cold, the boiler switches on, the room warms until it is too hot, the boiler switches off, the hot water in the radiators continues to provide heat which is now unwanted, the room cools until it is too cool, the boiler switches on, and the whole cycle repeats itself. The room thermostat also cannot reduce the water temperature from the boiler and therefore its energy efficiency. In contrast, weather compensation enables the boiler to respond to outside temperature changes and adjusts the radiator output accordingly, so that a constant temperature is maintained indoors.
For Viessmann boilers, it is a very simple addition and here we outline a few, simple practical considerations.
Sensor location: A north-facing wall is the ideal place for the weather compensation sensor because it’s shaded and the sensor’s measurements won’t get affected by direct sunlight. But north-east and north-west facing walls usually also have shaded areas suitable for the sensor. And if it’s necessary to use an east-, west-, or south-facing wall, the sensor can often be located in the shaded recess of a window-frame or window-reveal. If necessary, the sensor can be shaded beneath a purpose-made cover.
Radiators: If your project isn’t a new-build, you won’t have to buy new radiators. Because most boilers are installed as replacements, they typically get connected successfully to systems where radiators have traditionally been over-sized. If the previous boiler could heat the building with those radiators, the new boiler with weather compensation will also be able to.
Setting-up: This could hardly be easier! The sensor simply has to be attached to the outside wall by one or two screws; a wire from the sensor clips into two ports on the boiler control board (and the wire is low-voltage, so there’s no need for an electrician); and the boiler knows when the weather sensor is attached and automatically adjusts to weather compensation mode. All Viessmann Vitodens boilers have weather compensation software built into the controls and, since the introduction of the new Boiler Plus regulations, come with the sensor in the box.