A heat pump's ETAS, or seasonal space heating energy efficiency (ηs), is its efficiency over a heating season expressed against primary energy, as a percentage, whereas SCOP is expressed against the electricity consumed. That is why the same air-to-water heat pump shows an ETAS of 135 % and a SCOP of 3.45: both describe the same machine, on two scales linked by the 2.5 conversion coefficient set by Regulation (EU) No 813/2013. Comparing an ETAS with a SCOP without converting is like comparing euros with dollars. On the funding side, the French CEE measure sheets BAR-TH-171 and BAR-TH-172 require at least 126 % at low temperature and 111 % at medium or high temperature.
Heat pump ETAS: definition and calculation formula
ETAS reads as a percentage, never as a coefficient. It starts from the SCOP measured under EN 14825, divides it by the primary energy conversion coefficient (CC = 2.5), then subtracts the flat corrections set by Annex III of Regulation (EU) No 813/2013: 3 points for temperature controls, and 5 more points for a water-to-water or brine-to-water heat pump, which pays for the electricity of its ground-loop pumps.
The formula ηs = SCOP / 2.5 minus the corrections
| Heat pump type | ETAS formula | SCOP giving 126 % | SCOP giving 111 % |
|---|---|---|---|
| Air-to-water | ηs = SCOP / 2.5 × 100 − 3 | 3.23 | 2.85 |
| Water-to-water, brine-to-water | ηs = SCOP / 2.5 × 100 − 3 − 5 | 3.35 | 2.98 |
The last two columns invert the formula, SCOP = (ηs + corrections) × 2.5 / 100, to read the minimum SCOP behind the funding thresholds.
The ETAS to SCOP conversion table for an air-to-water heat pump
This table applies the formula above to an air-to-water heat pump, the 3-point correction included.
| ETAS shown | Corresponding SCOP |
|---|---|
| 125 % | 3.20 |
| 135 % | 3.45 |
| 145 % | 3.70 |
| 155 % | 3.95 |
| 165 % | 4.20 |
| 175 % | 4.45 |
The rule of thumb worth memorising: 10 points of ETAS are worth 0.25 of a SCOP. That is what lets you settle an argument on the spot when one supplier quotes ETAS and another quotes SCOP, without digging out the documentation. On a reversible unit the same conversation plays out in cooling mode around SEER and its classes.
ETAS, SCOP, COP, SEER: what each indicator measures
These acronyms do not answer the same question. SCOP, in one sentence, is the seasonal coefficient of performance: the heat delivered over a whole heating season divided by the electricity consumed over the same season.
| Indicator | What it measures | Unit | Reference text | What it is used to justify |
|---|---|---|---|---|
| COP | Heat produced over electricity drawn, at one test point (e.g. A7/W35) | Coefficient, no unit | EN 14511 | Comparing two models at the same point, checking output at A-7 |
| SCOP | Same ratio, over a weighted heating season | Coefficient, no unit | EN 14825 | Estimating annual electricity consumption |
| ETAS (ηs) | Seasonal efficiency on primary energy, corrections deducted | % | Regulation (EU) No 813/2013 | Energy class, CEE and MaPrimeRénov' eligibility |
| SEER | Cooling produced over electricity, over a cooling season | Coefficient, no unit | EN 14825 | Cooling-mode performance of a reversible unit |
Only ETAS can be relied on in a funding application. COP and SCOP, with the A7, A2 and A-7 points to check, are covered in our article on a heat pump's SCOP and COP, and behaviour at reduced output in COP at partial load.
ETAS: what exactly are we talking about?
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.
The energy label class grid
An ETAS figure does not read on its own: Annex II of Delegated Regulation (EU) No 811/2013 turns it into a class, and the scale differs depending on whether the generator works at medium or low temperature. The same product can therefore show two classes depending on the declared regime.
| Class | ETAS, medium temperature application | ETAS, low temperature heat pump at 35 °C |
|---|---|---|
| A+++ | ≥ 150 % | ≥ 175 % |
| A++ | 125 to 150 % | 150 to 175 % |
| A+ | 98 to 125 % | 123 to 150 % |
| A | 90 to 98 % | 115 to 123 % |
| B | 82 to 90 % | 107 to 115 % |
| C | 75 to 82 % | 100 to 107 % |
| D | 36 to 75 % | 61 to 100 % |
| E | 34 to 36 % | 59 to 61 % |
| F | 30 to 34 % | 55 to 59 % |
| G | < 30 % | < 55 % |
Two readings follow straight onto the quotation. A condensing gas boiler tops out around 92 to 94 % ETAS, so class A, and no fuel-fired boiler will ever clear the 98 % that opens class A+. And Regulation (EU) No 813/2013 sets the market floor at 86 % ETAS for a fuel-fired boiler rated at 70 kW or less, which in practice rules non-condensing low-temperature boilers out of new installations.
The two traps that distort the comparison
The first is the water temperature. An ETAS only means something alongside the flow temperature it was established at, typically 35 °C or 55 °C, and the gap between the two is considerable on the same machine. An ETAS quoted without its regime is an unusable figure, and yet that is the form in which it most often travels through sales documentation.
The second is the nature of the figure itself. ETAS is a conventional efficiency computed for a reference season, not a measurement of what the machine will do at your client's house. It says nothing about sizing, about the emitters' actual temperature, or about installation quality, which are the three things that will decide the bill. Two machines with the same ETAS installed differently will consume nothing like the same.
What that changes in practice: ETAS is for comparing products and checking eligibility, not for promising performance. On a quotation, state the ETAS with its flow temperature, taking the value from a catalogue whose technical characteristics are verified with the manufacturers, and talk about savings from the sizing, never from the label alone.
ETAS at 35 °C or 55 °C: which value to read
An air-to-water heat pump's product fiche gives at least two ETAS values: one for the low-temperature application (35 °C water outlet) and one for the medium-temperature application (55 °C), under the average climate. The right value is the one for the regime the installation is sized for, that is, the flow temperature the emitters need at the design temperature.
| Application under Regulation (EU) No 813/2013 | Water outlet | Typical emitters | Class grid | CEE threshold |
|---|---|---|---|---|
| Low temperature | 35 °C | Underfloor heating, low-temperature radiators | Low-temperature heat pump grid | 126 % |
| Medium or high temperature | 55 °C | Existing cast-iron or steel radiators | Medium-temperature grid | 111 % |
On recent air-to-water heat pumps, ETAS at 35 °C commonly sits between 160 and 200 %, and at 55 °C between 120 and 145 % (an order of magnitude taken from market product fiches, not a regulatory value). Quoting the 35 °C ETAS on radiators that will need 55 °C overstates the machine by some forty points and exposes the application to rejection. The choice of regime comes down to the emitters: see low- vs high-temperature heat pumps and their impact on emitters.
ETAS thresholds required for a heat pump in 2026
| Text | Heat pump covered | Minimum ETAS, low temperature | Minimum ETAS, medium or high temperature | Reading condition |
|---|---|---|---|---|
| CEE sheet BAR-TH-171 | Air-to-water | 126 % | 111 % | Average climate, heat pump alone without controls |
| CEE sheet BAR-TH-172 | Water-to-water, brine-to-water | 126 % | 111 % | Average climate, according to the collector fluid |
| Regulation (EU) No 813/2013 | Any heat pump placed on the market | 125 % (low-temperature heat pump) | 110 % | Ecodesign floor, not a funding criterion |
Both CEE sheets take the efficiency of the heat pump alone for space heating, excluding the control device. This is a frequent trap: the system label (the "package") adds the contribution of the control class to the heat pump's ETAS, up to 5 points for a class VIII. A heat pump at 124 % on its own remains ineligible at low temperature, even if its package shows 128 %. MaPrimeRénov' per measure, which decree No 2026-822 refocused on heat pumps for applications filed since 1 September 2026, also relies on the ETAS from the product fiche, with the technical criteria in force on the filing date.
Above the threshold, ETAS also sets the volume of kWh cumac under BAR-TH-171 (two bands since 2026: 111 to 140 %, then above), detailed in the 2026 changes to the air-to-water heat pump CEE sheet. For BAR-TH-172, see brine-to-water heat pumps with horizontal collectors.
Reading ETAS on a product fiche: the lines to check
The product information fiche required by Regulation (EU) No 811/2013, also available in the European EPREL database from the model reference, is the only document that is binding.
| Fiche line | Symbol | What you check |
|---|---|---|
| Seasonal space heating energy efficiency | ηs, in % | The value at the right regime (35 or 55 °C) and under the average climate |
| Rated heat output | Prated, in kW | Consistent with the heat loss at the design temperature |
| Bivalent temperature | Tbiv, in °C | The point below which the heat pump alone no longer covers the load |
| Operation limit temperature | TOL, in °C | Lower than the site's design temperature |
| Consumption outside active mode | POFF, PTO, PSB, PCK, in kW | Standby and crankcase heater, which weigh on ETAS |
| Control class | I to VIII | To be removed from the package ETAS to get back to the heat pump alone |
Record these lines for the exact reference of the outdoor unit and the hydraulic module: one range changes ETAS from one output to the next, and the pair invoiced is the one that gets checked.
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.
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
Funding: where seasonal efficiency comes into the supporting documents and datasheets
In funding applications, seasonal efficiency 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, output, ratings, etc.). The measure specification remains your compass, whichever scheme is paying. One clear document beats three vague ones.
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.
- Proof of certification, 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.
