Heat pump: heat better, spend less

A heat pump draws heat from a cold source — outdoor air or the ground — and delivers it at a higher temperature into the heating circuit, using electricity to run a compressor. The ratio between the heat energy produced and the electricity consumed is called the coefficient of performance: it varies with the temperature of the source, the flow temperature required and the condition of the installation, and is never a single value valid all year round.

Air-water models draw heat from outdoor air through a unit installed outside the home; they are simpler to install and suit most houses. Geothermal models draw heat from the ground via horizontal collectors or a vertical probe; their performance is more stable in winter, but they require heavier groundworks or drilling and more space or permits.

A heat pump performs better the lower the flow temperature required by the heating circuit. A well-insulated home fitted with oversized radiators or underfloor heating allows a moderate flow temperature; a poorly insulated home with small, old radiators forces the unit to run at high temperature, which reduces its performance. This is why a replacement project often includes an assessment of insulation and emitters, not just the heat generator.

The outdoor unit needs a clear location, sheltered from excessive snow build-up and far enough from property boundaries and neighbours' windows: the operating noise, moderate but continuous, is managed through distance, an anti-vibration base and the choice of a suitable model. Some municipalities apply distance or noise-level rules that should be checked before fixing the final location.

The capacity of the heat pump is determined by a heat loss calculation for the home, taking into account floor area, insulation, orientation, number of occupants and the region's reference outdoor design temperature. This assessment is not a per-square-metre formula: two houses of the same size can need very different capacities depending on their construction year and insulation.

An oversized heat pump cycles on and off too often, which wears the unit and reduces comfort; an undersized one struggles to cover cold spells. Insist that the heat load assessment and the capacity retained appear in writing in the quote, along with the assumptions behind the calculation.

A replacement generally follows these steps: technical site visit and heat load assessment, choice of unit type and location, detailed quote, ordering, removal of the old oil or gas boiler and its tank if applicable, installation of the new heat pump and adaptation of the hydraulic circuit, commissioning and adjustment. Removing an oil tank follows specific rules for draining and disposal that the company must know and document.

Depending on the municipality and the nature of the work, a communal permit may be required for siting the outdoor unit, particularly in protected areas or where the facade is altered; check with your municipality's technical department before finalising the project details.

Replacing a fossil-fuel heat generator with a heat pump is supported by Klimabonus Wunnen, which replaced the former PRIMe House programme in 2022; new homes fitted with a heat pump from the outset fall under a separate component of the same scheme, with its own conditions. The amounts and conditions in force when you apply are published on guichet.lu; do not rely on a figure quoted on a commercial site.

Free, independent energy advice is available from Klima-Agence, particularly useful when the project combines insulation, a heat pump and solar panels, since the order of the works affects the sizing of each system.

Check that the company holds a business permit for the relevant activity and professional liability insurance; our company profiles summarise the public information available. A complete quote states the type and capacity of the unit, the heat load assessment it is based on, the associated hydraulic works, removal of the old generator, commissioning, warranties and the timeline.

You describe your project in a few minutes on vert.lu, and we pass the request on to companies in our directory whose trade and coverage area match; those available get in touch to arrange a visit. The service is free for homeowners and comes with no obligation.