ηs, the seasonal space heating energy efficiency, is the EU Ecodesign metric expressing a heater's useful output as a share of the primary energy it consumes. For heat pumps it equals the SCOP divided by 2.5 (the EU electricity conversion factor) minus small corrections. Heat pumps must reach at least 110% — low-temperature units 125% — while condensing gas boilers manage about 92–94%.
What does ηs actually measure?
ηs — the seasonal space heating energy efficiency — expresses the useful space heating a heater delivers as a percentage of the primary energy it consumes, averaged over a heating season. Defined by Ecodesign Regulation (EU) 813/2013, it is the one number that lets a gas boiler, an oil boiler and a heat pump be compared on a single scale.
Because electricity is converted back to primary energy, a heat pump shows ηs values of roughly 125–190% while the best condensing gas boiler reaches about 94% — the arithmetic of moving heat instead of making it.
How is ηs calculated from the SCOP?
For electrically driven heat pumps, ηs equals the SCOP divided by the EU conversion coefficient CC = 2.5, minus corrections: 3% for temperature controls, plus a further 5% deduction for the ground-water pumps of brine- or water-source units. The factor 2.5 represents the assumed 40% average efficiency of European electricity generation.
Worked example: SCOP 3.8 → 3.8 ÷ 2.5 = 152% → minus 3% → ηs = 149%, which lands in class A++.
ηs is a declaration derived from laboratory SCOP testing; the field counterpart that your building actually achieves remains the JAZ.
What are the minimum ηs values under Ecodesign?
Since 26 September 2017, space heaters may only be placed on the EU market if they clear these floors:
| Product | Minimum ηs |
|---|---|
| Heat pump space heaters | 110% |
| Low-temperature heat pumps | 125% |
| Fuel boilers ≤ 70 kW | 86% |
| Direct electric boilers | capped near 40% by the 2.5 factor (100 ÷ 2.5) |
A low-temperature heat pump, in the regulation's definition, is a unit that cannot deliver 52 °C heating water at −7 °C reference conditions and is rated at a 35 °C outlet — which is why the same product family can carry two different ηs declarations for medium- and low-temperature application.
How does ηs set the energy label class?
The label classes of Regulation (EU) 811/2013 map directly onto ηs: A+++ starts at 150%, A++ at 125%, A+ at 98%, A at 90%, B at 82%. Nearly every heat pump therefore lands between A+ and A+++, while condensing boilers cluster in class A with 90–94%.
A revision rescaling heating labels to a plain A–G scale — with fossil boilers pushed toward the bottom classes and new pictograms for noise and smart readiness — completed public consultation in January 2026; check the current adoption status on EUR-Lex before relying on the new scale. The full label mechanics, including package labels with solar devices, are covered in the EU energy label guide.
Why does ηs matter beyond the label?
Subsidy schemes lean on it. Italy's Conto Termico requires heat pumps to exceed the EU 813/2013 seasonal-efficiency minimums by defined margins per size class, and several national programmes set ηs floors above the legal minimum as a funding condition. For specifiers the practical rule: compare ηs only at the same temperature application, because a 35 °C declaration always looks better than a 55 °C declaration for the identical machine. Manufacturers such as Solimpeks declare ηs for both applications in the mandatory product fiche, published in the EU EPREL database.
Frequently asked questions
Why can a heat pump have an efficiency above 100%?
Because most of its output is free environmental heat moved from air, ground or water — only the compressor's electricity counts as input. ηs converts that electricity into primary energy with the 2.5 factor, and even then a good heat pump delivers 1.2–1.9 units of heat per unit of primary energy.
Is ηs the same as the SCOP?
No. ηs is the SCOP divided by 2.5 and reduced by a 3% controls correction, so a SCOP of 3.5 corresponds to an ηs of about 137%. SCOP compares heat pumps with each other; ηs compares all heating technologies on one primary-energy scale.
What ηs does a good air-to-water heat pump reach?
Current units typically declare roughly 125–190% at 35 °C and 110–145% at 55 °C application. Anything above the 110% legal floor is compliant; above 125% earns A++ and above 150% earns A+++ on the current label.
Where do I find the ηs of a specific product?
On the energy label, in the product fiche and in the EU EPREL product database, always stated separately for medium-temperature (55 °C) and, where applicable, low-temperature (35 °C) application.