A presence detector does not switch heating off, it lowers a setpoint. The rule holds for every generator: wire into the thermostat input, as a volt-free contact or through the manufacturer's own interface, never into the emitter's supply, or you buy short cycling and a safety defect. On non-domestic work the expectation is no longer comfort but compliance: Approved Document L asks for controls zoned by space type, with independent time and temperature control and a commissioning record, and occupancy sensing is the cheapest way to satisfy that on intermittently used spaces.
Choosing the right detector to control your heating without overconsumption
Infrared, microwave or dual-technology detector: which holds up best on site?
On site, the infrared (PIR) detector is often the most reliable. It triggers on movement in its direct field and handles dust well if the housing is suitable. The microwave type "sees" through certain materials. Handy, but more prone to false triggers. Dual technology limits false positives, provided the settings are carefully tuned.
Detection zones, blind spots and mounting height: avoiding unnecessary triggers
Aim for useful coverage, not maximum coverage. Avoid axes facing windows, air outlets, heat sources. Follow the mounting height recommended by the manufacturer and run an operational test. Fine-tuning the hold time and sensitivity avoids turning on the heating for a simple pass-through.
Heating compatibility: electric radiators, underfloor heating, boiler and heat pump
The detector should control a setpoint, not cut power abruptly. On electric radiators, go through a thermostat or a pilot wire. On underfloor heating, favour a gradual setback. For boilers and heat pumps, use the thermostat input (dry contact or compatible protocol) with a delayed setback to avoid short cycles.
Settings that really drive savings: delay, light threshold and heating modes
Delay: finding the right balance between comfort and energy savings
With a presence detector, the delay decides how long the heating or backup heater stays on after the last movement. Too short, and you keep restarting endlessly. Too long, and you heat for nobody. Aim for a well-tuned setting based on usage. Short in a hallway. More generous in a room where there's little movement.
Light threshold: don't confuse lighting and presence for heating
The light threshold mainly serves to avoid turning lights on when it's already bright. For heating, light says nothing about occupancy. A bright living room can be empty, a dark bedroom can be occupied. Keep a coherent threshold for lighting, and control heating with presence, schedule and actual temperature.
Eco mode, setpoint setback and reheat: the simple settings that work
Eco mode works when the setback is clear-cut and programmed. A 1 °C drop is often enough to make a difference, without losing comfort. Set a gradual reheat before return times. You heat at the right time, not all day. To go further, see how a heating programmer helps fine-tune the heating time slots.
Installing a presence detector room by room: real retrofit cases
Entrances, hallways, toilets: the "passageway" rooms where heating can be tightly managed
In these areas, a detector mainly serves to avoid heating "for nobody". In a retrofit, it's often paired with a connected thermostat or electric radiators (pilot wire), with fine-tuned absence-delay settings. A short delay, often 2 to 5 minutes, is enough for a hallway or a toilet.
Bedrooms and offices: managing actual occupancy without cooling too fast
A bedroom isn't a hallway. With a detector, aim for a gradual drop rather than a sudden stop. Set a longer delay, for example 20 to 30 minutes, and limit the drop to 1 or 2 °C to keep gentle thermal inertia, especially in a poorly insulated house.
Damp rooms: installation and setting precautions to avoid faults
Bathroom, utility room, kitchen. Choose a detector suited to humidity (sufficient IP rating) and install it away from water areas, per NF C 15-100. Avoid aiming it at a shower, an extractor fan or a window to limit false triggers. Careful wiring and a secure installation prevent many callbacks.
Connecting the detector to the heating: reliable solutions and points of vigilance
Direct control vs. relay/contactor: securing the power and protecting the equipment
Avoid direct control of a radiator or a heating element. Instead, have the detector drive a modular relay or a contactor, sized for the circuit's current. You keep low-power control and limit wear on the outputs. Add a suitably rated protection device and clearly separate the power and control conductors. Relay, protective device and wiring are electrical line items in their own right: they are priced alongside the heating measure, in the same work plan, rather than tacked on afterwards.
Thermostat, pilot wire, thermostatic valve: options depending on the type of installation
For boilers, heat pumps or underfloor heating, connect instead to the thermostat input via a dry contact, or through a manufacturer interface. On electric radiators, the pilot wire allows Comfort, Eco or Frost-protection modes without cutting power abruptly. With a thermostatic valve, you need a motorised head, sometimes with a gateway.
Troubleshooting: common symptoms (continuous heating, random triggers) and fixes
If something's behaving oddly, check the wiring and the delay settings first.
- Continuous heating: NO/NC reversed, stuck relay, delay too long, detector poorly aimed.
- Random triggers: sensitivity too high, draughts, interference, unstable power supply.
- Nothing starts: thermostat input not compatible, pilot wire missing, contactor coil not powered.
Measuring and proving the savings in 2026: a simple method for tradespeople and clients
Before/after readings: kWh, heating time and perceived comfort, without complicated equipment
Before the works, note the heating kWh from the bill or the Linky portal, the thermostat setpoint, and the time to go from 17 to 19 °C. After the works, repeat the same measurement over a comparable period. Add a comfort log (draughts, noise, humidity) validated by the client.
Where the savings are most realistic: year-round occupied homes, rentals, tertiary premises
Gains are more credible in a home occupied all year round, with stable usage. In a rental, do a quick review of settings and ventilation, then compare using monthly readings. In tertiary buildings, target controllable circuits and fixed schedules. Keep the same temperature setpoint to compare.
Good handover practice: explaining the detector and locking in the settings
At handover, give a one-page sheet with instructions, programming, maintenance, and where to read the kWh. Explain the detector (presence, opening) and what it triggers. Then lock in the sensitive settings (heating curve, limits) to avoid drift, while leaving a simple mode for everyday use.
