A water heater's energy class is derived from the water heating energy efficiency ηwh, and the scale that turns that figure into a letter changes with every declared load profile. Table 1 of Annex II to Commission Delegated Regulation (EU) No 812/2013 sets it out: class A starts at 38 % in profile S and at 65 % in profile M. Storage tanks are governed by a second scale, based on standing loss S expressed in watts. Since 26 September 2017, ecodesign has capped that standing loss at the class C boundary, which makes it impossible to place a tank rated D or below on the market.
What the class actually measures
ηwh, the efficiency that carries the class
The class of a water heater reflects one indicator only, the water heating energy efficiency ηwh, measured over a standardised 24-hour tapping cycle. It is neither an instantaneous COP, nor a combustion efficiency, nor an isolated production efficiency. For a solar or heat pump water heater, ηwh is calculated under average climate conditions per Annex VIII of the regulation, which is why the same machine shows different figures in cold and warm climates.
The load profile sets the scale
The load profile is not a rough indication of consumption, it is the test cycle itself. Each profile has a reference energy Qref, defined in Annex III to Regulation 814/2013.
| Profile | 3XS | XXS | XS | S | M | L | XL | XXL | 3XL | 4XL |
|---|---|---|---|---|---|---|---|---|---|---|
| Qref (kWh) | 0.345 | 2.100 | 2.100 | 2.100 | 5.845 | 11.655 | 19.07 | 24.53 | 46.76 | 93.52 |
XXS, XS and S share the same reference energy and differ only in how the tappings are spread across the day. The profile the manufacturer declares is therefore a choice of test cycle, and it is that choice which then dictates the scale applied.
Two labels are still in circulation
The printed scale changed on 26 September 2017 without any threshold moving. Units registered before that date carry an A to G label, those registered after an A+ to F label. For water heaters alone, the calculation scale runs all the way up to A+++, a level no direct electric unit can reach. Seeing two different labels on two data sheets does not mean one of them is out of date.
The class table, profile by profile
The table worth keeping to hand
Thresholds for ηwh in per cent, from Table 1 of Annex II to Regulation 812/2013. Profiles 3XL and 4XL exist under ecodesign but have no labelling class at all.
| Class | 3XS | XXS | XS | S | M | L | XL | XXL |
|---|---|---|---|---|---|---|---|---|
| A+++ | 62 | 62 | 69 | 90 | 163 | 188 | 200 | 213 |
| A++ | 53 | 53 | 61 | 72 | 130 | 150 | 160 | 170 |
| A+ | 44 | 44 | 53 | 55 | 100 | 115 | 123 | 131 |
| A | 35 | 35 | 38 | 38 | 65 | 75 | 80 | 85 |
| B | 32 | 32 | 35 | 35 | 39 | 50 | 55 | 60 |
| C | 29 | 29 | 32 | 32 | 36 | 37 | 38 | 40 |
| D | 26 | 26 | 29 | 29 | 33 | 34 | 35 | 36 |
| E | 22 | 23 | 26 | 26 | 30 | 30 | 30 | 32 |
| F | 19 | 20 | 23 | 23 | 27 | 27 | 27 | 28 |
Each figure is the lower bound of its class: the class runs up to the threshold of the class above, and anything below the F row is class G.
Why some thresholds exceed 100 %
In profiles M to XXL, class A+ and above start beyond 100 %. That is not a typo: ηwh compares useful energy delivered against energy consumed, and a heat pump or solar machine returns more than it draws in electricity. Those levels are out of reach for a direct electric water heater, which is precisely what the 2018 ecodesign step on the large profiles confirmed.
What ecodesign already rules out
Regulation 814/2013 sets minima that the class makes visible but which apply independently of it.
| Declared profile | 3XS | XXS | XS | S | M | L | XL | XXL | 3XL | 4XL |
|---|---|---|---|---|---|---|---|---|---|---|
| Since 26/09/2015 | 22 | 23 | 26 | 26 | 30 | 30 | 30 | 32 | 32 | 32 |
| Since 26/09/2017 | 32 | 32 | 32 | 32 | 36 | 37 | 37 | 37 | 37 | 38 |
| Since 26/09/2018 | n/a | n/a | n/a | n/a | n/a | n/a | n/a | 60 | 64 | 64 |
The 2018 step on the large profiles is what pushed direct electric out of XXL installations and above: at a 60 % minimum ηwh, only heat pump, solar and gas condensing units qualify.
Storage tanks have their own scale
Standing loss is a power, not a consumption
The regulation defines standing loss S as the thermal power dissipated by the tank at given water and ambient temperatures, expressed in watts. Any data sheet quoting it in kWh per 24 hours has performed a conversion, useful for a client but not the regulatory figure. It is the value in watts you need to record, because that is what lets you recalculate the class.
The eight formulas of Table 2
Hot water storage tank classes, Annex II point 2 of Regulation 812/2013, with V the storage volume in litres.
| Class | Standing loss S, in watts |
|---|---|
| A+ | S < 5,5 + 3,16 × V^0,4 |
| A | 5,5 + 3,16 × V^0,4 ≤ S < 8,5 + 4,25 × V^0,4 |
| B | 8,5 + 4,25 × V^0,4 ≤ S < 12 + 5,93 × V^0,4 |
| C | 12 + 5,93 × V^0,4 ≤ S < 16,66 + 8,33 × V^0,4 |
| D | 16,66 + 8,33 × V^0,4 ≤ S < 21 + 10,33 × V^0,4 |
| E | 21 + 10,33 × V^0,4 ≤ S < 26 + 13,66 × V^0,4 |
| F | 26 + 13,66 × V^0,4 ≤ S < 31 + 16,66 × V^0,4 |
| G | S greater than 31 + 16,66 × V^0,4 |
The class C boundary, 16,66 + 8,33 × V^0,4, is exactly the cap that point 2.1 of Annex II to Regulation 814/2013 has imposed since 26 September 2017. A new tank can therefore no longer come out below class C.
What that means in watts
Values calculated from the Table 2 formulas, rounded to one decimal place.
| Volume | A+ threshold | A threshold | B threshold | Regulatory cap, class C bound |
|---|---|---|---|---|
| 50 L | 20.6 W | 28.8 W | 40.4 W | 56.5 W |
| 100 L | 25.4 W | 35.3 W | 49.4 W | 69.2 W |
| 200 L | 31.8 W | 43.9 W | 61.4 W | 86.0 W |
| 300 L | 36.4 W | 50.1 W | 70.1 W | 98.2 W |
| 500 L | 43.5 W | 59.5 W | 83.2 W | 116.7 W |
A 200-litre tank at 85 W is compliant and class C, while at 31 W it is A+. Turned into energy, the 54 W gap represents roughly 470 kWh a year, directly comparable to the storage losses that the French EPC reference table attributes to the cylinder.
Checking a quoted class before you commit
What EPREL shows
The Commission's EPREL database publishes a sheet for every registered model. For a water heater you get the class, the declared load profile and the ηwh efficiency, including its cold and warm climate variants. For a tank you get the standing loss in watts and the volume, which are exactly the two inputs you need to redo the class calculation yourself.
The traps on a product data sheet
- A class quoted without a load profile means nothing, and that is the first missing item to ask for.
- A standing loss given in kWh per 24 hours is a conversion, not the regulatory figure.
- Storage water heaters on the small profiles are volume-capped, at 7 litres in 3XS, 15 litres in XXS and XS, and 36 litres in S.
- An A to G label and an A+ to F label can sit side by side on two competing models without either being out of date.
What belongs on the estimate
Exact commercial reference, declared load profile, class, and for a separate tank the standing loss in watts together with the volume. A line reading "class A 200 L water heater" commits to nothing and cannot be verified. None of it has to be retyped once the reference carries it: Argile builds your catalogue from verified manufacturer data, load profile and class included, and carries them through to the quote line. On the wording and mandatory items of a works estimate, see the mandatory information on a renovation works quote.
What the class does not tell you on site
A well-classed profile chosen badly is still chosen badly
Class A+ in profile S describes a unit that performs well over a small-draw cycle. Installed for a family of four, it will be pushed outside its test envelope and comfort will drop without the class having lied. The profile follows from the simultaneous draws recorded during the survey, and the volume is set afterwards, as covered in the article on DHW storage volume.
The room drives the real performance of a heat pump unit
The ηwh of a heat pump water heater is measured under average climate conditions. In a confined, poorly ventilated or cold room, real performance falls away and the electric backup takes over. Available air volume, duct routing and condensate drainage are survey items, to be settled before the reference is chosen.
The product label is not the building label
The product class comes from European regulation, the building's rating comes from a national assessment method. Both use the same letters and neither measures the same thing. No product class guarantees a band improvement, and nothing of the sort should be written on an estimate. On the neighbouring subject of distribution losses, see the DHW recirculation loop.
