What a class B building automation system actually requires (EN ISO 52120)

“Class B or better” appears more and more often in specifications, incentive schemes and energy regulations. Building automation class B is shorthand for a level of control that EN ISO 52120-1, the successor to EN 15232, defines in detail. Yet many installers and building owners are unsure what it actually requires.

In this article we explain the four classes, what class B means for a heating system, why rules and incentives refer to it, and what documentation to prepare. Incentive rules differ from country to country and change often: always check the official sources for your location.

The building automation classes

EN 15232, now incorporated into EN ISO 52120-1, sorts building automation and control systems (BACS) into four classes.

• Class D: no automation. Systems without controls, or with manual controls only.
• Class C: standard automation. This is the reference class: for example, a central thermostat switching the heat source on and off.
• Class B: advanced automation. Individual room control, coordination between zones and the heat source, energy management functions.
• Class A: high performance. Integrated control based on real demand and continuous monitoring.

The standard gives efficiency factors for each class. For heating energy in a residential building they are 1.10 for class D, 1.00 for C, 0.88 for B and 0.81 for A. Moving from class C to B therefore cuts estimated heating demand by about 12%, as we saw when looking at how much zone control saves.

What class B requires

Class B is not a product: it is a set of functions the system must have. For heating, the most important are:

• temperature control in each room, with a sensor and a control per room or zone;
• coordination between zones and heat generation, for example a flow temperature that follows actual demand;
• time scheduling, with different modes for day and night, occupied and unoccupied;
• pump control based on demand;
• monitoring: the ability to see how the system is running and to intervene.

The class is assessed on the finished system, not on a single device. An excellent controller installed without room sensors does not make class B.

Why regulations refer to it

In the European Union, the Energy Performance of Buildings Directive requires building automation and control systems in larger non-residential buildings. The 2018 revision introduced the obligation for buildings whose heating or combined heating and ventilation systems exceed 290 kW, and the 2024 recast extends it to systems above 70 kW by 2029. Member states transpose these rules, often using the EN ISO 52120 classes as the yardstick.

Incentive schemes follow the same logic. In Italy, for example, the tax deduction for home automation (the “bonus domotica”) requires the control system to be at least class B, and to let occupants see energy consumption, view operating conditions and switch on, switch off and schedule the heating remotely. The Italian Conto Termico 3.0 scheme also covers BACS with minimum class requirements. Other countries have similar schemes with their own conditions.

The functions that make the difference

When a system falls short of class B, it is usually for one of three reasons.

• No room control. A single thermostat, however smart, cannot be class B.
• Zones not linked to the heat source. Room thermostats that work independently, with a boiler running at a fixed temperature, miss the coordination requirement.
• No monitoring. Without data on how the system runs and what it uses, there is nothing to manage.

All three are about how the system is designed, not about any particular brand.

Documentation to prepare

Whatever the scheme, the paperwork tends to follow the same pattern:

• invoices describing the devices and the work;
• technical documentation for the devices, including data sheets;
• a declaration of the class achieved, from the supplier or from a qualified engineer, depending on the scheme;
• a description of the system: zones, sensors, control strategies, monitoring;
• proof of payment in the form the scheme requires.

Keep everything together. Inspections can come years after the work.

A practical example

Take a detached house with six underfloor heating loops, a condensing boiler and a single thermostat in the living room: a class C system. To bring it up to class B, in short, you need:

• a sensor in each zone and an actuator on each loop, so every room has its own control;
• a controller that coordinates the zones with the boiler and the pump, and adjusts the flow temperature according to demand and outdoor temperature;
• time schedules for each zone, editable from the app;
• energy metering, for example a gas meter with a pulse output or data read from the boiler, with regular reporting to the occupants.

These are exactly the elements of the upgrade described in other articles on this blog. The difference, for regulatory and incentive purposes, is that they must be documented: which functions were implemented, and how.

For larger non-residential buildings the same logic applies on a bigger scale: more zones, more meters, and usually a written control strategy for each system, from heating and cooling to ventilation and lighting.

Common mistakes

• Assuming a product “is class B”. Classes apply to systems. A data sheet claiming class B means the device can be part of a class B system, if installed properly.
• Missing functions. A smart thermostat without consumption display, or a system without room control, does not meet the requirements.
• Incomplete records. Data sheets, diagrams and declarations should be stored with the project files.

How a Brick system is documented

Brick controls the zones, coordinates the heat source, runs the schedules and logs consumption and temperatures, visible in the app and in Grafana, as in the plant room dashboard. These are the functions the requirements describe.

But the class is assessed on the finished system: it depends on how many zones there are, how the heat source is connected and which readings are collected. So for every project we provide installers and engineers with the configuration’s documentation: diagrams, data sheets and a description of the functions. The final assessment rests with the engineer who signs it off.

This article describes technical requirements and is not tax or legal advice.