ETAS: what exactly are we talking about?
A simple definition of ETAS and how it differs from "full load" efficiency
ETAS, or seasonal energy efficiency, measures a generator's average performance over a heating season. It factors in partial-load operation, stops, and certain auxiliaries. By contrast, "full load" efficiency is a measurement under lab conditions, at rated power. With ETAS, you get closer to a home's actual use.
Which generators ETAS applies to (boilers, heat pumps, water heaters, etc.)
ETAS applies to equipment covered by ecodesign rules and the energy label. This mainly covers boilers (gas, oil, biomass), heat pumps, hybrid systems, and certain "packaged" generators with controls. For domestic hot water, the indicators used are often close to efficiency, depending on the draw-off profile.
Why seasonal efficiency matters on a job site (real use, weather variations)
On site, the unit rarely runs flat out. Weather, flow temperature, controls, on/off cycling and, for a heat pump, defrost phases, change everything. ETAS helps compare solutions on a realistic basis and secure consistency between sizing, emitters, and settings.
How ETAS is calculated: what makes seasonal efficiency vary
Calculation conditions and operating profiles (shoulder seasons, half-load, stops)
ETAS corresponds to a seasonal efficiency calculated over a typical year. Tests are run at several operating points, including half-load, with shoulder-season phases and stops. Results are weighted by a climate profile (warm, average, cold) and a flow temperature (for example 35°C or 55°C), to get closer to real-world use.
Losses accounted for (standby, modulation, auxiliaries, cycling)
The calculation includes losses that don't show up in an instantaneous COP. It accounts for standby and off periods, auxiliary consumption (circulator, fan), modulation outside the optimal zone, and cycling losses when the unit repeatedly starts and stops. More stable control limits these penalties and improves ETAS.
Data to look for on the energy label and the manufacturer's datasheet
On the energy label, look for the seasonal efficiency (ηs or SCOP), the reference climate, the design load (Pdesignh), and the noise level. On the manufacturer's datasheet, check the COP at several points (A7, A2, A-7), standby consumption, the modulation range, and the control system information.
Choosing and sizing your generators correctly using ETAS
Sizing: avoiding oversizing and short cycling that penalise ETAS
ETAS reflects seasonal efficiency, and therefore real performance over a year. An oversized generator spends its time stopping and restarting. This short cycling drags down efficiency and increases wear. Base your sizing on a rigorous heat-loss estimate and the local design temperature. Target a unit that can modulate down low, close to mid-season needs.
Controls and emitters: the right settings that improve seasonal efficiency
Controls often gain you more than an extra 1 kW would. A well-set heating curve, a modulating thermostat, and emitters suited to low temperature pull ETAS upward. On condensing systems, aim for cold returns. On heat pumps, limit the flow temperature and take care with schedules and setbacks.
Installation and commissioning: points to watch (hydraulics, balancing, flow temperature)
On site, check the flow rates, sludge removal if needed, filtration, bleeding, then balancing. Calibrate the heating curve and the flow temperature ceiling. Fine-tuning at commissioning, with recorded readings, avoids losing ETAS in the field.
ETAS, grants and requirements: what may change in 2026 for your applications
MaPrimeRénov' and CEE: where ETAS comes into the supporting documents and datasheets
In grant applications, ETAS mainly serves to link the installed product to a measurable performance. In 2026, expect more checks on the consistency between the invoice, the product datasheet, the exact reference, and the characteristics (efficiency, power, ratings, etc.). For CEE, the standardised operation fiche remains your compass. For MaPrimeRénov', the logic is the same. One clear document beats three vague ones.
RGE and inspections: proving the stated performance without piling up documents
RGE inspections rarely look at paperwork alone. They look for proof on site. Photos, settings, commissioning, and material traceability make the difference. Aim for a file that's light but complete, with a single clear thread. That's the best defence in case of field inspections.
2026 checklist: documents to prepare (label, instructions, certificate, job-site photos)
To avoid back-and-forth, prepare a clean file from the technical visit onward.
- Energy label and manufacturer's instructions.
- RGE certificate, insurance, detailed invoice (brand, model, quantities).
- Completion certificate and, if requested, ETAS document or technical opinion.
- Dated photos before, during, after. Including the nameplate for equipment.
Concrete cases: improving seasonal efficiency on site
Condensing boiler: settings and heating returns to make the most of condensation
Simple goal. Keep the heating return low to condense often. Aim for a return temperature around 50 to 55°C or lower in mid-season. Adjust the heating curve, lower the flow setpoint, open the thermostatic valves, and balance the network to avoid radiators that are "hot at the top, cold at the bottom." Clean maintenance and good settings often gain more than replacing the equipment.
Heat pump: heating curve, buffer tank (if needed) and mid-season optimisation
On a heat pump, the heating curve is your steering wheel. The lower the water temperature, the higher the seasonal COP climbs. In mid-season, avoid on/off cycling by lowering the slope, widening the hysteresis, and favouring stable control. The buffer tank is only useful if you have short cycling or unstable flow rates. Otherwise, it can degrade performance. Keep continuous operation where possible.
Replacement vs whole-house renovation: when ETAS isn't enough to guarantee performance
ETAS gives you a lab snapshot. On the ground, a leaky envelope, oversized emitters, missing MVHR, or poor sizing can crash seasonal efficiency. Before a simple replacement, check losses, airtightness, insulation, and controls. A well-sequenced whole-house renovation, with an energy audit, secures the result and limits callbacks. That's where the real gain is decided.
Key figures
150 to 200%
ETAS low-temp air/water heat pump
36 to 40%
ETAS electric water heater
92 to 98%
ETAS condensing boiler
Frequently asked questions
Requirements vary by CEE fiche and equipment category, but a common benchmark is a condensing gas boiler with a seasonal efficiency (ηs) generally ≥ 92% (class A). For heat pumps, performance is judged more through the SCOP (often class A+ to A+++), with minimum values set by the grant frameworks and the product datasheet. Before quoting, check the energy label and the datasheet for the exact model (commercial reference), since that's what counts.
Louis Meneteau
CPO of Argile
