KfW funding programs (BEG \u2013 Bundesf\u00f6rderung f\u00fcr effiziente Geb\u00e4ude) provide investment grants for heat pump retrofits, with bonus rates for replacing oil heating systems.<\/li>\n<\/ul>\nAustria (\u00d6sterreich)<\/strong><\/p>\n\n- The Austrian Erneuerbare-W\u00e4rme-Gesetz (EWG) targets fossil fuel phase-out in heating. Oil and gas heating systems may no longer be installed in new buildings. Replacement requirements in existing buildings are phased in by federal state (Bundesland) energy laws.<\/li>\n
- The KlimaBonus program offers direct subsidies for heat pump installation as part of Austria’s climate policy.<\/li>\n
- OIB Richtlinie 6 (Energieeinsparung und W\u00e4rmeschutz) provides the energy efficiency framework governing building and installation standards.<\/li>\n<\/ul>\n
Switzerland (Schweiz)<\/strong><\/p>\n\n- The Mustervorschriften der Kantone im Energiebereich (MuKEn 2014) introduced the obligation that when a fossil fuel heating system is replaced, the new system must cover at least 10% of its energy demand from renewable sources. Many cantons have adopted stricter requirements.<\/li>\n
- The L\u00e4rmschutzverordnung (LSV) regulates noise emissions relevant to air source heat pump outdoor units.<\/li>\n
- Cantonal energy legislation (Kantonale Energiegesetze) determines specific retrofit obligations at regional level.<\/li>\n<\/ul>\n
German-speaking Italy (S\u00fcdtirol \/ Alto Adige)<\/strong><\/p>\n\n- Provincial climate and energy plans align with Italian national targets under the Piano Nazionale Integrato per l’Energia e il Clima (PNIEC), which targets significant renewable heat penetration by 2030.<\/li>\n
- KlimaHaus standards (equivalent to Austrian\/German low-energy building certification) set energy performance benchmarks that influence retrofit design requirements.<\/li>\n<\/ul>\n
Technical Drivers<\/h3>\n
Beyond regulation, the technical case for retrofit is rooted in system efficiency and long-term operating cost. Heat pumps deliver a Coefficient of Performance (COP) between 2.5 and 5.0 in typical operating conditions. For every 1 kWh of electricity consumed, the system delivers 2.5 to 5.0 kWh of thermal energy. A gas boiler operates at a maximum efficiency of approximately 0.98 (98%), burning one unit of fuel to produce less than one unit of heat. The thermodynamic advantage of a heat pump is structural, not marginal.<\/p>\n
The growing availability of renewable electricity \u2014 through grid decarbonisation, solar PV, and smart tariffs \u2014 amplifies this advantage over time. A gas boiler locked into gas infrastructure cannot benefit from falling renewable electricity costs. A heat pump can.<\/p>\n
<\/span>Key Features of Retrofit Existing Heating<\/span><\/h2>\nRetrofit existing heating is defined by six core features. Each feature determines the technical scope, cost, and performance outcome of the installation.<\/p>\n
Hydraulic System Assessment<\/h3>\n
Definition:<\/strong> Hydraulic system assessment is the systematic evaluation of the existing pipework, emitter circuit, and heat distribution network to determine compatibility with heat pump operation.<\/p>\nPurpose:<\/strong> Heat pumps operate most efficiently at low flow temperatures \u2014 typically 35\u00b0C to 55\u00b0C, compared to 70\u00b0C to 90\u00b0C for a gas boiler. The existing distribution system must be capable of delivering adequate heat output at these reduced temperatures.<\/p>\nBenefits:<\/strong> A thorough hydraulic assessment prevents undersized heat distribution, avoids unnecessary emitter replacement, and ensures the heat pump operates within its optimal efficiency range. It reduces installation cost and risk by identifying specific upgrade requirements rather than assuming a full system replacement is necessary.<\/p>\nPractical Application:<\/strong> The installer calculates the heat loss of each room according to DIN EN 12831 (or \u00d6NORM EN 12831 in Austria). The heat output of each existing radiator is then evaluated at the target flow temperature. Where existing radiators have sufficient oversizing relative to the original design, they can deliver adequate heat at 45\u00b0C or 50\u00b0C without replacement. Where they cannot, targeted replacement or supplementary emitter installation is required.<\/p>\nLow-Temperature Emitter Compatibility<\/h3>\n
Definition:<\/strong> Low-temperature emitter compatibility describes the capacity of radiators, underfloor heating circuits, or fan coil units to deliver the required room heat load at the lower flow temperatures characteristic of heat pump systems.<\/p>\nPurpose:<\/strong> Emitters designed for high-temperature systems are physically larger than required. This apparent disadvantage becomes an advantage in retrofit: larger radiators deliver more heat at lower temperatures than their nameplate rating suggests when derated to heat pump operating conditions.<\/p>\nBenefits:<\/strong> Many existing radiator installations in DACH building stock \u2014 particularly panel radiators installed during the 1990s through 2010s \u2014 have significant oversizing relative to the actual heat load. This oversizing directly enables low-temperature heat pump retrofit without full emitter replacement.<\/p>\nPractical Application:<\/strong> The Voith-K\u00fcbler method and EN 442-2 radiator derating curves are applied to calculate actual radiator output at reduced flow temperatures. A radiator rated at 1,000 W at 75\/65\u00b0C flow\/return and 20\u00b0C room temperature delivers approximately 480\u2013520 W at 50\/40\u00b0C. If the room heat loss at design conditions is 450 W or below, no replacement is necessary.<\/p>\nFlow Temperature Optimisation<\/h3>\n
Definition:<\/strong> Flow temperature optimisation is the process of setting and controlling the heat pump’s heating curve (Heizkurve) to deliver the minimum flow temperature necessary to meet the building’s heat demand at any given outdoor temperature.<\/p>\nPurpose:<\/strong> The lower the flow temperature, the higher the heat pump’s COP. Every 1\u00b0C reduction in flow temperature improves heating COP by approximately 2\u20133%. Flow temperature optimisation is therefore the primary lever for maximising seasonal system efficiency (SCOP\/SPF).<\/p>\nBenefits:<\/strong> Optimised flow temperature management reduces annual electricity consumption, lowers operating costs, and extends compressor service life by reducing cycling frequency and pressure ratios. It also reduces thermal stress on pipework and fittings.<\/p>\nPractical Application:<\/strong> iDM heat pumps with Navigator 2.0 control systems implement weather-compensated heating curves with automatic adaptation. The control system measures outdoor temperature continuously and adjusts the flow temperature set point along the configured curve. During commissioning, the installer sets the design flow temperature at design outdoor temperature (typically \u221212\u00b0C to \u221215\u00b0C in DACH climates) and the reduced flow temperature at milder conditions. The Navigator 2.0 system learns building thermal behaviour over time and refines curve parameters automatically.<\/p>\nDomestic Hot Water Integration<\/h3>\n
Definition:<\/strong> Domestic hot water (DHW) integration is the configuration of the heat pump to produce hot water for sanitary use, either through a dedicated DHW heat exchanger, a combined buffer and DHW cylinder, or a separate indirect-fired storage cylinder.<\/p>\nPurpose:<\/strong> In retrofit installations, the existing DHW cylinder must be assessed for compatibility with heat pump output temperatures. Many older cylinders were sized for gas or oil boilers producing water at 80\u00b0C or above. Heat pumps operating with a monovalent configuration may require a larger storage volume or supplementary electric immersion element to meet peak DHW demand.<\/p>\nBenefits:<\/strong> Integrating DHW production into the heat pump system eliminates the need for a separate gas or electric DHW appliance, reduces installation complexity, and enables solar PV integration for low-cost DHW heating during daylight hours.<\/p>\nPractical Application:<\/strong> \u00d6NORM EN 15450 (Austria) and DIN EN 15450 (Germany) provide design guidelines for DHW systems integrated with heat pumps. iDM TERRA and AERO series systems support DHW temperatures up to 65\u00b0C (with electric boost to 70\u00b0C for legionella protection cycles) through their integrated control systems. The Navigator 2.0 controller can schedule legionella protection cycles automatically in compliance with hygiene regulations.<\/p>\nElectrical Infrastructure Upgrade<\/h3>\n
Definition:<\/strong> Electrical infrastructure upgrade involves assessing and adapting the building’s electrical supply \u2014 meter, consumer unit, cabling, and earthing \u2014 to support heat pump operation.<\/p>\nPurpose:<\/strong> Heat pumps require a reliable three-phase or single-phase electrical connection depending on rated capacity. Outdoor unit cables must meet voltage drop requirements. Smart grid-capable systems require data infrastructure. Time-of-use tariff integration requires compatible metering.<\/p>\nBenefits:<\/strong> A properly dimensioned electrical installation ensures heat pump reliability, enables smart grid-ready operation, supports grid-connected PV systems, and complies with national wiring regulations (\u00d6VE\/\u00d6NORM E 8001 in Austria, DIN VDE 0100 in Germany, NIN in Switzerland).<\/p>\nPractical Application:<\/strong> For most residential heat pumps in the 5\u201315 kW range, a 16A or 25A three-phase supply is sufficient. Heat pump-specific tariffs (W\u00e4rmepumpentarif) available from Austrian and German grid operators reduce operating costs significantly and may require separate metering. The installer coordinates with the network operator (Netzbetreiber) for connection approval and metering configuration.<\/p>\nControl System Integration<\/h3>\n
Definition:<\/strong> Control system integration is the configuration of the heat pump’s control unit to manage the heat distribution system, DHW production, weather compensation, smart grid signals, and any residual auxiliary heating components.<\/p>\nPurpose:<\/strong> A retrofit installation frequently inherits existing zone controls, thermostatic radiator valves (TRVs), and room thermostats. These must be coordinated with the heat pump controller to avoid conflicting demands and short-cycling.<\/p>\nBenefits:<\/strong> Properly integrated controls maximise system SCOP, enable remote monitoring and diagnostics, support demand response participation, and provide the homeowner with a single interface for the entire heating system.<\/p>\nPractical Application:<\/strong> iDM’s Navigator 2.0 control system integrates weather compensation, zone management, DHW scheduling, and Smart Grid-Ready (SG Ready) signal handling in a single platform. The SG Ready interface allows the system to respond to grid operator signals \u2014 increasing or reducing heat pump load in response to grid conditions or renewable electricity price signals, pre-heating the building when electricity is cheap and green.<\/p>\n<\/span>Types of Retrofit Existing Heating Installations<\/span><\/h2>\nRetrofit installations are categorised by the source of environmental heat the heat pump extracts. Each type carries specific civil engineering requirements, efficiency profiles, and suitability criteria.<\/p>\n
Air Source Heat Pump Retrofit (Luftw\u00e4rmepumpe)<\/h3>\n
An air source heat pump (ASHP) extracts heat from ambient outdoor air. The outdoor unit contains a fan, heat exchanger coil, and in most configurations the compressor. The indoor unit contains the hydraulic connections, expansion vessel, controls, and buffer storage.<\/p>\n
Suitability:<\/strong> ASHP retrofit is the most accessible type for existing buildings because it requires no groundwork. Outdoor unit placement follows regulations on noise (TA L\u00e4rm in Germany, \u00d6NORM EN ISO 9614-2 and local Bauordnung in Austria, LSV in Switzerland) and setback distances from property boundaries.<\/p>\nRelevant iDM Products:<\/strong> iDM AERO AL series (air-to-water, modulating inverter compressor) and iDM TERRA AL (air source with high DHW capability) are designed for retrofit conditions, operating reliably down to \u221220\u00b0C ambient temperature.<\/p>\nEfficiency Profile:<\/strong> Seasonal COP (SCOP) in DACH climates typically 2.8\u20134.0 depending on flow temperature and climate zone.<\/p>\nGround Source Heat Pump Retrofit (Erdw\u00e4rmepumpe)<\/h3>\n
A ground source heat pump (GSHP) extracts geothermal energy from the ground through a brine loop \u2014 either horizontal ground collectors (Fl\u00e4chenkollektor) or vertical borehole heat exchangers (Erdw\u00e4rmesonde).<\/p>\n
Suitability:<\/strong> GSHP retrofit is appropriate where garden space is available for horizontal collectors or where borehole drilling is permitted. Borehole installation requires regulatory approval under Wasserrecht (water law) in Austria and Germany, and Gew\u00e4sserschutzgesetz in Switzerland. Drilling depth and method are subject to cantonal and federal geological constraints.<\/p>\nRelevant iDM Products:<\/strong> iDM TERRA SW (brine-to-water heat pump) is designed for ground source applications. The TERRA SW series operates at higher COPs than air source systems due to the more stable ground temperature compared to ambient air.<\/p>\nEfficiency Profile:<\/strong> SCOP in DACH climates typically 3.5\u20135.0 depending on brine inlet temperature and flow temperature.<\/p>\nHybrid Heat Pump Retrofit (Hybride W\u00e4rmepumpe)<\/h3>\n
A hybrid heat pump system combines a heat pump with an existing gas or oil boiler. The heat pump covers the base load; the boiler provides peak demand coverage when outdoor temperatures fall below the heat pump’s bivalence point (Bivalenzpunkt).<\/p>\n
Suitability:<\/strong> Hybrid retrofit is used when the existing heating distribution system cannot be adapted for low-temperature operation and full heat pump coverage would require extensive emitter replacement. It is also applicable where building envelope thermal performance is insufficient to support a monovalent heat pump in peak winter conditions without oversized equipment.<\/p>\nRegulatory Note:<\/strong> Under Germany’s GEG 2024, hybrid systems using a gas boiler are subject to the 65% renewable energy requirement. The heat pump component must cover sufficient energy share to meet this threshold. In Austria, EWG provisions set comparable minimum renewable share requirements.<\/p>\nEfficiency Profile:<\/strong> Overall system efficiency depends on the split between heat pump and boiler operating hours. A well-designed hybrid system achieves 60\u201380% of heat pump operating hours annually.<\/p>\nExhaust Air Heat Pump Retrofit (Abluft-W\u00e4rmepumpe)<\/h3>\n
An exhaust air heat pump extracts heat from the warm exhaust air stream of a mechanical ventilation system. The heat pump produces both space heating and DHW from ventilation exhaust heat.<\/p>\n
Suitability:<\/strong> Exhaust air heat pumps are suitable for well-insulated retrofit buildings with low specific heat demand (typically below 40\u201360 kWh\/m\u00b2a) and mechanical ventilation systems. They are common in Passive House and near-Passive House retrofit scenarios.<\/p>\nLimitation:<\/strong> The available heat source is limited by the exhaust air volume flow rate. Buildings with high heat demand relative to floor area are not suited to exhaust air heat pump systems without supplementary heat sources.<\/p>\n<\/span>Use Cases for Retrofit Existing Heating<\/span><\/h2>\nResidential Single-Family Homes (Einfamilienh\u00e4user)<\/h3>\n
The dominant retrofit scenario in DACH markets. A gas or oil boiler installed in the 1990s or 2000s reaches end of life. The homeowner replaces the system under GEG, EWG, or cantonal energy law obligations. The existing wet distribution system \u2014 radiators or underfloor heating \u2014 is assessed for low-temperature compatibility. An air source heat pump is installed with minimal civil engineering. KfW BEG or KlimaBonus funding supports the investment.<\/p>\n
Multi-Apartment Buildings (Mehrfamilienh\u00e4user)<\/h3>\n
Central heating retrofit in apartment buildings involves higher hydraulic complexity. Zone balancing, staircase riser redesign, and individual metering (Heizkostenabrechnung, required under German Heizkostenverordnung and Austrian equivalent regulations) must be integrated with the heat pump system. Ground source systems with borehole arrays are common where garden or parking area is available.<\/p>\n
Commercial and Light Industrial Buildings<\/h3>\n
Office buildings, retail premises, and light industrial units with existing gas heating undergo retrofit as part of corporate sustainability reporting requirements under CSRD (Corporate Sustainability Reporting Directive, EU 2022) and national green procurement frameworks. The scale of these installations typically involves larger GSHP systems or multiple air source units in cascade configuration.<\/p>\n
Buildings in Historic Protection Zones (Denkmalschutz)<\/h3>\n
Historic buildings in protected areas face additional constraints. External alterations to the facade or garden may require approval from the Denkmalschutzbeh\u00f6rde (monument protection authority). Outdoor unit placement and noise must meet both standard residential zoning requirements and heritage protection conditions. iDM AERO units with low-noise operating modes and compact outdoor units address this use case.<\/p>\n
<\/span>Benefits of Retrofit Existing Heating with a Heat Pump<\/span><\/h2>\nEnergy Efficiency and Cost Reduction<\/h3>\n
Heat pumps reduce heating energy costs by 40\u201370% compared to gas or oil heating at current energy price differentials in DACH markets. The seasonal performance factor (SPF or JAZ \u2014 Jahresarbeitszahl) measures actual annual system efficiency. A well-commissioned retrofit with iDM equipment typically achieves a JAZ of 3.0\u20134.5, meaning 3\u20134.5 units of heat delivered per unit of electricity consumed.<\/p>\n
Carbon Emission Reduction<\/h3>\n
Direct CO\u2082 emissions from heating fall to zero at the point of use upon removal of the gas or oil boiler. Lifecycle emissions depend on the electricity grid carbon intensity. Austria’s electricity mix \u2014 with high hydropower share \u2014 provides particularly low lifecycle emissions for heat pump operation. Germany’s grid decarbonisation trajectory under Energiewende further improves the carbon case over system lifetime.<\/p>\n
Future-Proof Regulatory Compliance<\/h3>\n
Buildings retrofitted with heat pumps comply with current and foreseeable future energy and climate legislation across DACH markets. This protects property values and avoids the risk of future mandatory retrofit obligations with associated compliance costs.<\/p>\n
Energy Independence and Price Stability<\/h3>\n
Heat pumps reduce dependence on gas and oil imports, which are subject to geopolitical price volatility \u2014 as demonstrated by European energy markets in 2021\u20132023. Electricity prices are more stable and increasingly linked to domestic renewable generation rather than international commodity markets.<\/p>\n
Compatibility with Solar PV<\/h3>\n
Retrofitted heat pump systems integrate directly with photovoltaic systems. The heat pump can absorb surplus PV generation through Smart Grid Ready control interfaces, producing heat or pre-heating DHW storage during periods of excess solar generation. This reduces grid export, maximises self-consumption, and reduces operating costs.<\/p>\n
Increased Property Value<\/h3>\n
In DACH real estate markets, buildings with heat pump heating and high energy performance certificates (Energieausweis) command measurable price premiums. German and Austrian energy performance legislation requires disclosure of heating system type in property listings, making the heat source directly visible to buyers and tenants.<\/p>\n
<\/span>Selection Criteria for Retrofit Heat Pump Systems<\/span><\/h2>\nSelecting the appropriate heat pump type and specification for a retrofit installation depends on five primary criteria.<\/p>\n
Building Heat Loss<\/h3>\n
The design heat load (Normheizlast) calculated in accordance with DIN EN 12831 or \u00d6NORM EN 12831 determines the required heat pump capacity at design outdoor temperature. Undersizing results in insufficient heating coverage; oversizing leads to short-cycling, reduced efficiency, and higher capital cost. Accurate heat loss calculation is mandatory before equipment selection.<\/p>\n
Key inputs include building geometry, wall and roof U-values, window specifications, infiltration rate, ventilation type, and the design outdoor temperature for the climatic location. The design outdoor temperature varies significantly within DACH geography: \u221212\u00b0C in Munich, \u221216\u00b0C in Vienna, \u221220\u00b0C or below in Alpine locations such as Innsbruck or Davos.<\/p>\n
Existing Distribution System Flow Temperature<\/h3>\n
The maximum flow temperature the heat pump must achieve to deliver the building’s heat demand determines the heat pump’s operating range and directly affects efficiency. Systems retaining high-temperature emitters may require flow temperatures of 60\u00b0C or above, which demands a heat pump capable of high-temperature operation or necessitates emitter upgrades to reduce the required flow temperature.<\/p>\n
iDM AERO and TERRA series heat pumps cover a flow temperature range of up to 65\u00b0C in standard operation, with high-temperature variants available for demanding retrofit conditions.<\/p>\n
Available Heat Source<\/h3>\n
Ground source systems provide higher efficiency but require land area or drilling permits. Air source systems are universally applicable but subject to noise regulations governing outdoor unit placement. The selection between air and ground source depends on plot size, soil geology, regulatory approval timeline, and installation cost.<\/p>\n
Electricity Supply Infrastructure<\/h3>\n
Three-phase supply availability, connection capacity, and tariff options affect both equipment selection and operating economics. Single-phase heat pumps up to approximately 7\u20138 kW are available for buildings without three-phase supply. Buildings with existing three-phase supply from industrial or agricultural use can accommodate larger heat pump capacities.<\/p>\n
Funding Eligibility<\/h3>\n
In DACH markets, grant funding significantly affects the economic case for retrofit. Equipment specification must meet the efficiency thresholds required for funding eligibility. In Germany, BEG (Bundesf\u00f6rderung f\u00fcr effiziente Geb\u00e4ude) requires a seasonal COP (Jahresarbeitszahl) of at least 1.7 as a minimum threshold, with higher efficiency attracting higher grant rates. Austrian KlimaBonus funding has comparable eligibility criteria. Swiss cantonal energy programs apply similar energy efficiency requirements.<\/p>\n
<\/span>Comparison: Retrofit vs New-Build Heat Pump Installation<\/span><\/h2>\n<\/div>\n\n
\n\n\n| Criterion<\/th>\n | Retrofit Installation<\/th>\n | New-Build Installation<\/th>\n<\/tr>\n<\/thead>\n |
\n\n| Starting condition<\/td>\n | Existing heating infrastructure in place<\/td>\n | No prior heating system<\/td>\n<\/tr>\n |
\n| Design freedom<\/td>\n | Constrained by existing pipework, emitters, and building envelope<\/td>\n | Full design freedom<\/td>\n<\/tr>\n |
\n| Civil engineering<\/td>\n | Minimal (ASHP) to moderate (GSHP borehole)<\/td>\n | Planned as part of construction<\/td>\n<\/tr>\n |
\n| Emitter selection<\/td>\n | Assessment and selective replacement<\/td>\n | Designed to heat pump operating conditions<\/td>\n<\/tr>\n |
\n| Flow temperature target<\/td>\n | Constrained by existing emitters; optimised through assessment<\/td>\n | Designed for low-temperature from outset<\/td>\n<\/tr>\n |
\n| Typical SCOP<\/td>\n | 2.8\u20134.0 (ASHP); 3.5\u20135.0 (GSHP)<\/td>\n | 3.5\u20135.0 (ASHP); 4.0\u20136.0 (GSHP)<\/td>\n<\/tr>\n |
\n| Installation timeline<\/td>\n | 1\u20133 days (ASHP); 3\u201310 days (GSHP with borehole)<\/td>\n | Integrated into construction schedule<\/td>\n<\/tr>\n |
\n| Regulatory complexity<\/td>\n | Existing building regulations, heritage constraints, neighbour notifications<\/td>\n | Standard new-build approval process<\/td>\n<\/tr>\n |
\n| Funding eligibility<\/td>\n | Full access to retrofit-specific funding programs<\/td>\n | New-build funding programs apply<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n |