Weather compensation varies the flow temperature according to outdoor temperature and a heating curve: that is what Delegated Regulation (EU) No 811/2013 calls a class III, VI or VII temperature control. A room thermostat, however recent and connected, falls under class I or IV and does not provide weather compensation, since it works on room temperature rather than on the weather. It is the class, not the brand, that belongs on the quotation, because it is enforceable and because it separates two proposals that otherwise look identical.
Understanding the role of an outdoor sensor in weather compensation
What the sensor actually measures: outdoor temperature in the right spot
The outdoor sensor doesn't "guess" the climate. It measures an air temperature, useful only if it's mounted in the right spot, sheltered from direct sun and from nearby air discharges. Otherwise, the sensor reads too warm or too cold, and the regulation gets it wrong.
How regulation adjusts flow temperature based on the heating curve
With weather compensation, the controller translates outdoor temperature into heating flow temperature. When it's colder outside, it raises the flow temperature. When it warms up, it lowers it. The curve's slope and offset are adjusted to match the building and the emitters. The result: the system heats "at the right level" instead of running all-or-nothing.
Concrete on-site benefits: comfort, consumption, stability
On a heat pump, the heating curve is not a comfort setting, it is the parameter that decides the seasonal COP: every degree saved on flow temperature shows up in the client's bill and in the performance you stated on the quotation. It is also your best protection against the most common callback, compressor short cycling in the shoulder seasons. Two habits to build into commissioning. Record the slope and offset you settled on, together with the outdoor temperature on the day and the measured flow temperature, and put them on the commissioning certificate. Then schedule a return visit at the first real cold spell, because a curve set in October is worth nothing until it has seen the design outdoor temperature, the figure carried by the heat loss calculation to BS EN 12831-1 that Argile produces from the survey.
Choosing and placing your sensor correctly: the detail that changes everything
Recommended location: facade, height, areas to avoid (sun, wind, exhaust)
The goal is to measure an "average" temperature, not a wall heated by the sun. The location is settled before anything is drilled.
Validate the location before drilling
- North-facing facade or northwest, about 2 to 3 m from the ground.
- No direct sunlight, and not under an overhang that traps heat.
- Away from a window, a mechanical ventilation extractor, a flue, or a heat pump air discharge.
- Neither a corner heavily exposed to prevailing winds, nor an area where water runs down.
Wired or wireless sensor: advantages, limits and use cases in renovation
Two families, two installation trade-offs.
| Criterion | Wired sensor | Wireless sensor |
|---|---|---|
| Signal reliability | the most stable, no radio waves, reliable over time | actual range depends on walls, risk of interference |
| Power | no battery | battery maintenance to plan for |
| Installation | you need to run a cable, which can be tricky in renovation | simplified when running conduit isn't possible |
Compatibilities to check: boiler, heat pump, controller and connection terminals
Before buying, check manufacturer compatibility. Expected sensor type (often NTC), dedicated terminals on the controller, possible polarity, and parameters to enable on the boiler or heat pump side.
The ErP control classes: which ones really use an outdoor sensor
When a client compares two quotes, the "controls" line means nothing until you give its class. Delegated Regulation (EU) No 811/2013 defines eight temperature control classes, and only some of them rely on an outdoor sensor and a heating curve. It is the reference to quote, because it is enforceable and because it separates a room thermostat from genuine weather compensation.
| Class | What the control does | Outdoor sensor |
|---|---|---|
| I | on-off room thermostat, starts and stops the heat generator | no |
| III | weather compensator for on-off heaters, varies the flow temperature setpoint with outdoor temperature and the selected heating curve | yes |
| IV | PID room thermostat for on-off heaters, electronically adjusts cycle time and on-off ratio from room temperature | no |
| VI | weather compensator with room sensor, for modulating heaters, with parallel shift of the curve to improve comfort | yes |
| VII | weather compensator with room sensor, for on-off heaters | yes |
| VIII | multi-sensor room control, three sensors or more, varies flow temperature from the cumulative deviation of the sensors, modulating output | no |
Remember too that classes VI and VII combine an outdoor sensor with a room sensor, which lets the curve be corrected without resetting it every season, and that is often the best compromise in retrofit work where the fabric is poorly known. On a heat pump, the heating curve drives the COP directly, as covered in our article on the heating curve.
On-site settings: configuring weather compensation with method
Setting the slope and curve offset without spending weeks on it
Start simple. Continuous heating over 24 hours, thermostatic radiator valves open, and the outdoor sensor well placed. First adjust the offset to get the correct indoor temperature in mild weather, then the slope to hold comfort in cold weather. Make small adjustments, then let it run 24 to 48 hours before judging. Otherwise, you're correcting for noise, not for actual need.
Adjusting based on emitter type: radiators, underfloor heating, mixed systems
With radiators, the curve is often "steeper" because water temperature needs to rise higher. With underfloor heating, keep a gentler curve and limited flow temperatures to avoid discomfort. In mixed systems, separate the circuits if possible. A direct circuit for radiators, a mixed circuit for the floor. You gain in stability.
Checking the result: temperatures, cycles, client feedback and fine adjustments
Check three things. Actual indoor temperature, flow temperature, and number of start-ups. Too many short cycles usually means a curve set too high. Insufficient comfort in severe cold, slope set too low. Make fine adjustments. Explain to the client that you're aiming for a home with "soft light." Stable, without yo-yoing.
Troubleshooting: common sensor faults and outdoor temperature errors
Typical symptoms: overheating, underheating, on/off cycling, setpoint drift
Inconsistent temperature: an outdoor sensor often drives the weather compensation. If it drifts or fails, the heat pump can heat too hard, not enough, or cycle on/off repeatedly. On the display, the outdoor temperature jumps by several degrees, or stays frozen. Before touching the curve, compare the displayed value with a thermometer placed in the shade.
Simple tests: continuity, ohmic value, cable fault, radio interference
Basic measurements, in order, before touching a single parameter.
Checking a suspect sensor
- Cut the power.
- Check continuity to the board, then the sensor's ohmic value against the manufacturer's table (often an NTC): a near-infinite or near-zero resistance indicates a cut cable or a short circuit.
- Also inspect terminals, corrosion, moisture.
- Gently pull on the cable, a loose contact is common at the cable gland.
- Keep the cable away from 230V wiring and dimmers, interference can distort the reading.
- If the sensor is wireless, test batteries, pairing, distance and metal obstructions.
Special cases: influence of an indoor sensor, thermostatic valves and balancing
Hybrid regulation: if an indoor sensor is active, it can correct the weather compensation curve and mask an outdoor fault. Thermostatic valves that are closed too much cause flow to drop, the heat pump quickly rises in temperature then shuts off. Open the reference radiator, check the bypass and rebalance the system, otherwise the setpoint drifts like a compass near a magnet.
What changes in 2026: requirements, financial aid and best practices to highlight for your clients
In 2026, how outdoor temperature-based regulation strengthens real-world performance
A well-tuned heat pump or boiler is one whose consumption matches actual need. Outdoor temperature-based regulation continuously adjusts "weather compensation." With an outdoor sensor, you avoid swings, stabilize comfort and limit short cycles, which are often synonymous with losses.
Link with subsidized projects: consistency with quality requirements and applications
In 2026, financial aid and CEE applications increasingly require consistency between the equipment installed, the settings and proof of commissioning. Highlight the pairing of regulation and configuration. It's a measurable quality that secures the job, especially in whole-house renovation.
Client pitch: explaining the outdoor sensor simply, with supporting evidence (readings)
Put it simply. The sensor is the "thermometer outside" that drives the flow temperature. Show 2 readings, before and after. A lower flow curve, less overheating, and a visible saving over a few days, without promising a magic number.
