This KNX FAQ answers the questions we hear most from homeowners, architects, and integrators across Europe, drawing on real installations our own teams have designed, wired, and programmed — grouped by topic so you can jump straight to what matters.

These are the questions we hear most from homeowners, architects and integrators sizing up KNX — answered plainly, based on real installations our own teams have designed, wired and programmed. KNX is the open, internationally certified building-automation standard used right across Europe, and we have grouped the questions by topic so you can jump to whatever matters for your project. When you’re ready, you can request a quote and we’ll take it from there.

Wiring and installation

How many wires does KNX actually need?

The bus itself runs on a single dedicated cable — a green, KNX-certified twisted pair, usually a 2x2x0.8 mm low-voltage SELV cable. That one cable carries both the communication and the small amount of power the sensors need. Mains loads like lights and motors are wired separately to their actuators, while the bus quietly links every device together.

What cable and length limits should I plan for?

Standard KNX uses the certified green bus cable (KNX TP). A single line can stretch to roughly 1000 metres in total, with up to about 350 metres between any two devices, and carries up to 64 devices before you add a power supply or extend the line. Bigger buildings are simply broken into more lines and areas — which is why KNX scales just as comfortably from a flat to a campus.

Can KNX go into a house that’s already finished?

Yes, retrofits are common. Where pulling fresh bus cable would mean real disruption, we lean on wireless KNX RF and hybrid wired-plus-wireless designs to add automation without tearing the place apart. The best route depends on your walls, ceilings and goals — exactly what we assess during a consultancy visit before quoting.

ETS programming and ownership

What is ETS?

ETS, the Engineering Tool Software, is the official, manufacturer-independent program used to design, configure and commission every KNX installation. Because all KNX devices are programmed through the same tool, any certified integrator can pick up a properly documented project — which is one of the real freedoms of an open standard.

How long does the programming take?

It depends on size and complexity. A focused apartment might be commissioned in a day or two, while a large home or a commercial building — HVAC, blinds, lighting scenes, energy logic — can run to a week or more. Good design up front shortens commissioning noticeably, which is precisely why we plan thoroughly before touching the bus.

Do I own the ETS file for my system?

Yes — and you should insist on it. The ETS project file is the documented blueprint of your installation. Own it, and any KNX professional can maintain or expand your system with no lock-in to a single company. We hand the ETS project over as part of our integration services.

KNX versus WiFi, and security

How is KNX different from a WiFi smart home?

WiFi smart-home gadgets lean on your router, your internet and usually a manufacturer’s cloud. KNX runs locally on a dedicated wired bus, so it keeps working even when the internet is down, and it is built for thousands of switching cycles over decades. WiFi is fine for gadgets; KNX is built-in building infrastructure.

Is KNX secure, and does it depend on the cloud?

KNX works locally and doesn’t need the cloud to function, which keeps the attack surface small and your data private. For sensitive projects, KNX Secure layers on encrypted, authenticated communication (KNX Data Secure and IP Secure). The result is a system that’s both reliable and private by design.

Can I still control KNX from my phone?

Of course. You get local control from wall switches and panels, and you can add app or voice control through a secure IP gateway whenever you want remote access. The difference from a pure WiFi setup is that the building carries on working even when that remote layer isn’t available.

What KNX can control

Can one KNX system handle HVAC, blinds and energy together?

Yes — that’s one of its real strengths. The same bus manages lighting, heating, cooling and ventilation, motorised blinds and shutters, plus energy metering and load management, all coordinated. Because everything shares one standard, a single scene or schedule can combine climate, shading and lighting intelligently for both comfort and efficiency.

What exactly is an actuator?

The actuator is the device that does the physical work — switching a light, dimming it, driving a blind motor, opening a heating valve — acting on commands it receives over the bus. Sensors and switches send the instruction; actuators are the muscle that carries it out.

What’s the integrated-relay advantage I keep hearing about?

Some KNX brands, Letour among them, build the switching relay straight into the device rather than relying on separate actuator modules in the panel. That trims wiring, frees up space in the distribution board and cuts installation labour — lowering overall project cost without ever stepping outside the KNX standard. We’re happy to advise where it fits in your design.

Maintenance and service

How much looking-after does KNX need?

Honestly, very little. The hardware is built to a strict certification standard with low failure rates, and there are no mandatory subscriptions or forced cloud updates hanging over you. Most of the service work over a system’s life is adding features or adjusting logic rather than fixing faults — and any change is made cleanly in the ETS project.

What happens if a single device fails?

Because KNX is decentralised, one faulty device doesn’t take the whole system down — the rest of the bus carries on. The failed unit is swapped out and reprogrammed from your documented ETS project, so you’re back to normal quickly. That resilience is a big part of why KNX suits demanding installations.

Can you work on projects right across Europe?

Yes. Our teams design, install and program KNX installations throughout Europe — and because it’s an open standard with a documented ETS file, your system stays serviceable by any certified professional afterward. You’re never tied to us, which is rather the point.

Request a quote and we’ll answer anything specific to your building.