According to figures published by the European Heat Pump Association (EHPA) on 6 August 2026, 2.9 million domestic heat pumps were sold across 21 European countries in 2025 – 13% more than in 2024. The turnaround ended two years of decline: the demand created by the 2022 gas price shock faded through 2023 and 2024 as energy prices eased and several Member States narrowed their support schemes. The current growth is driven by lower taxes on electricity, the phase-out of fossil fuel subsidies and, once again, a high gas price level.
Replacement is therefore accelerating – and with it a design error that recurs across the market: the heat pump goes in behind an unchanged building envelope. This analysis examines why the order of the works governs the outcome of the investment, and where thin-film insulation belongs within it.
Heating takes most of household energy – and in Hungary it comes largely from natural gas.
These figures describe the demand side rather than the equipment: they show how large a share heating takes in the household energy balance, and which fuel a heat pump displaces. This analysis does not compare heat pump types. It examines the temperature level at which the plant has to work – which is a question of building physics, not of plant selection.
The coefficient of performance is governed by the building’s heat loss, not by the plant that serves it
A heat pump does not generate heat but transports it, raising ambient heat to the temperature of the heating system. Its coefficient of performance (COP) is therefore governed by the temperature difference between the source and the emitter side: the larger that difference, the lower the COP.
The source temperature is not open to choice: outdoor air is set by the weather, ground and groundwater by the local geology. The emitter-side temperature is not an input but a result: it is the heating flow temperature, and it is established by the building’s design heat loss together with the emitter surface area already installed.
For a fixed emitter surface, the greater the building’s heat loss, the higher the flow temperature needed to reach the same indoor temperature. In an uninsulated or poorly insulated building the design heat loss is large and the existing radiators were sized for boiler operation, so the system typically has to run at 55–70 °C. Heat pumps, by contrast, reach their most favourable coefficient of performance at flow temperatures around 35 °C.
A rule of thumb used widely in design practice holds that above 55 °C, each further degree of flow temperature costs roughly 2–2.5% of the coefficient of performance. No standard fixes that figure, but it captures the order of magnitude reliably. The same plant in the same building therefore delivers a very different seasonal coefficient of performance (SCOP) depending on the temperature level at which it has to operate.
Where the expected saving is lost
A low coefficient of performance is not merely a technical characteristic; it is a direct operating cost. In most Member States electricity carries appreciably higher taxes and levies than natural gas, and only a high coefficient of performance can offset that difference. It is precisely for this reason that the European Commission’s Electrification Action Plan set a target electricity-to-gas price ratio of 2.5 for households by 2030.
While electricity costs several times as much as gas per unit of energy, a heat pump running at a flow temperature of 55–65 °C can match or exceed the heating cost of the gas boiler it replaced: across that range the coefficient of performance is not high enough to close the price gap.
The second consequence appears in sizing. With heat loss unchanged, the design heat output stays high, which means a machine of greater capacity, a higher capital cost and more noise. At part load it also brings more frequent starts and stops, and those degrade the seasonal coefficient of performance further. The number of units in a cascade often reflects not the size of the building but the fact that the envelope was never improved.
This is the point at which owners conclude that the heat pump has disappointed. The fault, however, rarely lies with the plant: the heat pump serves exactly the temperature level the building demands of it, and that level is prescribed by the thermal condition of the envelope.
The correct design sequence: envelope improvement precedes plant replacement
In a new building the question does not arise, because envelope and plant are designed together: well-performing constructions give a low design heat loss, a large emitter – typically underfloor heating – works at a low flow temperature, and the plant can be modest in capacity. In an existing building the same order becomes a decision, and that decision governs the return on the investment.
The physics is the same, run in reverse: if the building’s heat loss falls, the same emitter surface reaches the same indoor temperature at a lower flow temperature. No other intervention moves the seasonal coefficient of performance as far, and it reduces the plant capacity required at the same time – so it saves on two counts, in running cost and in capital cost alike. The emitters stay as they are; only the temperature they run at changes.
Where external board insulation can be built, that is the correct technical answer for a heat pump retrofit too. A thicker layer delivers a greater reduction in heat loss and therefore a lower flow temperature; a thin-film coating is no substitute for it. The question arises where a board system cannot be applied: on articulated or listed facades, in dense terraced settings where scaffolding meets constraints on the public highway, and in occupied buildings that cannot be taken out of use. Across that part of the stock the envelope work is today simply left undone – and the heat pump is then installed behind it.
This is the case GWR NANO INSULATION® addresses. At 1 mm dry film thickness it does not alter facade articulation or opening dimensions; it is applied by airless spray, on low and medium-height buildings typically without scaffolding, and the building can remain occupied throughout. Its thermal performance is documented in TÜV SÜD external monitoring report 3229268: in the comparative field test at Dunabogdány – measurement by the testing and calibration laboratory of MEOLIT Kft., in January and February 2021, on three identically built test houses – the coated house used 43% less heating energy than an uninsulated reference house and 9.5% less than a 10 cm EPS-insulated one. Moisture behaviour warrants separate consideration on the existing stock: the coating remains vapour-open (sd = 0.40 m, class V2), so it does not close off the outward drying of the enclosing structure.
The scope of that report must be stated precisely: determining thermal transmittance and conductivity values was outside its remit, and the report does not treat its own field test as an internationally standardised procedure. A further limit matters even more here: no measured data exists on the coating’s effect on flow temperature or on a heat pump’s coefficient of performance. The argument above therefore rests on the physics of the system – the measured reduction in heating demand is the quantity that moves the flow temperature downwards – but no numerical COP improvement can be derived from it.
Engineering conclusions
Three conclusions follow from the planning of a heat pump retrofit, each building on the last.
- At system level: the coefficient of performance cannot be read off the equipment data sheet. It follows from the temperature level the building demands. Before the plant is selected, the flow temperature at which the system will operate after the intervention has to be established.
- In economic terms: while electricity carries higher taxes and levies than gas, the running-cost advantage appears only at a high coefficient of performance. Behind an unchanged envelope the capital cost is higher too, because a larger plant capacity is needed.
- In building-physics terms: where board insulation can be built, it delivers the greater reduction in heat loss. Where geometry, heritage protection or operation rule it out, thin-film, structurally non-invasive insulation is the only intervention by which the temperature level can be reduced before the plant is replaced.
A heat pump can be the most efficient element of a heating system – but only at the temperature level the building permits. The first step in the investment decision is therefore not selecting the plant, but establishing how far the flow temperature can be brought down.
The tightening of European Union building energy obligations, and the ban on incentives for fossil fuel boilers, are set out in our post on the EPBD proceedings. The EU building renovation framework and its climate policy context are examined in the analysis of RRF climate expenditure, and the energy-system effects of the summer cooling side in the post on the EU hydrological drought. Documented installations in Hungary and abroad are set out on the References page.
GWR NANO INSULATION® is distributed in Hungary and the Central and Eastern European region by Summotive® (Summa Technologiae Kft.). TÜV SÜD test reports, the Declaration of Performance, and technical data sheets are available on request.