Heat pumps have become the dominant low‑carbon heating technology in many markets. In several European countries, including the UK and Ireland, they are now the primary heat source in a large share of new homes, and the global market reached around 70 billion US dollars in 2024.

This development has several drivers: rising fossil fuel prices, growing environmental awareness, increasingly strict building energy regulations and attractive subsidy schemes. On top of that, technical progress has made heat pumps more efficient and quieter.

This 2026 guide explains how heat pumps work, compares the different types, looks at current costs and incentives, and gives guidance on correct sizing. You will also find links to our in‑depth specialist articles on individual topics.

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What is a heat pump?

A heat pump is a device that moves heat from a lower to a higher temperature level. The principle is identical to that of a refrigerator – only the objective is reversed: while a fridge extracts heat from its interior and releases it to the room, a heat pump extracts heat from the environment and transfers it to the heating system.

The cycle in four phases

The heat pump cycle consists of four successive phases:

Phase	Component	Process	State of refrigerant
1	Evaporator	Absorbs heat from the source	Liquid → Gaseous
2	Compressor	Raises pressure and temperature	Gaseous (hot)
3	Condenser	Releases heat to heating system	Gaseous → Liquid
4	Expansion valve	Reduces pressure and temperature	Liquid (cold)

The refrigerant runs through this cycle continuously. It absorbs heat at low temperature and releases it again at higher temperature. The compressor is the only component that requires electrical energy.

A detailed explanation of the physical principles is given in the article The Anti‑Fridge: How Does a Heat Pump Work?.

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Main components at a glance

Every heat pump consists of the same basic components working together in a closed circuit:

Component	Function	Characteristics
Evaporator	Takes up heat from the source (air, ground, water)	Large‑area heat exchanger
Compressor	Compresses the refrigerant	Electrically driven, main energy consumer
Condenser	Transfers heat to the heating system	Compact heat exchanger
Expansion valve	Reduces pressure and temperature	Throttling device, maintenance‑free
Refrigerant	Transports the heat	Evaporates at low temperature

Refrigerants in transition

Traditional refrigerants such as R410A have a high global warming potential (GWP). Modern heat pumps increasingly use R290 (propane) with a GWP of only 3 (compared with 2088 for R410A). R290 is flammable, so charge sizes are limited and safety distances must be observed.

You will find more detail on each component in the article Components: Heat Exchangers, Compressor and Expansion Valve.

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Types of heat pump compared

Heat pumps are classified according to their heat source and the medium used to distribute heat in the building. The three most common types for residential buildings are:

Air‑to‑water heat pump

An air‑to‑water heat pump extracts heat from the outdoor air and transfers it to the heating water. In the UK and Ireland this is by far the most common type for homes.

Advantages:

• Relatively low installation cost
• Usually no specific permit required
• Flexible siting (outdoor or indoor unit)
• Quick installation

Disadvantages:

• Efficiency falls at low outdoor temperatures
• Noise from the outdoor unit
• Higher running costs than ground source systems

Ground source (brine‑to‑water) heat pump

A ground source heat pump uses the relatively constant temperature of the ground. Heat is collected via horizontal ground loops or vertical boreholes.

Advantages:

• Highest efficiency (stable source temperature)
• Very quiet (no outdoor fan unit)
• Can provide passive cooling in summer
• Lowest running costs

Disadvantages:

• High upfront cost (especially for boreholes)
• Permits often required for boreholes or groundwater abstraction
• Large garden area needed for horizontal collectors
• Longer design and construction period

Air‑to‑air heat pump

An air‑to‑air heat pump heats the indoor air directly without a water circuit. In Europe this is often installed as a reversible air‑conditioning system.

Advantages:

• Can heat and cool
• Low investment cost
• Responds quickly to temperature changes

Disadvantages:

• Does not provide domestic hot water
• Requires ductwork or multiple indoor units
• Typically less efficient than water‑based systems for whole‑house heating

Comparison of heat pump types

Indicative cost ranges are given in euros; UK and Irish prices are broadly comparable in sterling.

Criterion	Air‑to‑water	Ground source	Air‑to‑air
Upfront cost	10,000–20,000 €	18,000–35,000 €	8,000–15,000 €
Seasonal performance (SCOP/JAZ)	3.0–4.0	4.0–5.0	2.5–3.5
Space requirement	Low	High (groundworks)	Low
Permit required	Rarely	Often (boreholes, groundwater)	Rarely
Hot water	Yes	Yes	No
Cooling	Optional	Passive possible	Yes
Noise	Outdoor unit audible	Very quiet	Indoor units audible
Best suited for	New build, many retrofits	New build with suitable plot	Supplementary heating/cooling

You can find more on the different types and how to combine them with solar PV in Heat Pump Types and the Dream Team with Solar.

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Key performance figures: COP, SCOP, seasonal efficiency

The efficiency of a heat pump is expressed using several key figures. Understanding these values is essential for assessing and comparing systems.

COP – Coefficient of Performance

The COP is an instantaneous value measured under standardised test conditions (e.g. A2/W35 = 2°C outdoor air, 35°C flow temperature).

Calculation:

COP = Heat output (kW) ÷ Electrical input (kW)

A COP of 4 means: 1 kW of electricity produces 4 kW of heat.

SCOP – Seasonal Coefficient of Performance

The SCOP takes into account different operating points over an entire heating season and is more meaningful than a single COP value. It is determined in Europe according to EN 14825 and shown on the EU energy label.

Seasonal efficiency in practice (JAZ)

In German literature the term Jahresarbeitszahl (JAZ) is used for the measured annual performance factor of an installed system. In the UK and Ireland, the equivalent concept is the seasonal performance factor (SPF) or seasonal efficiency of the heat pump system over a year. It includes all operating conditions, part‑load operation and auxiliary electricity.

General formula:

Seasonal performance factor = Useful heat delivered (kWh/year) ÷ Electricity consumed (kWh/year)

Interpreting seasonal performance

Seasonal factor (SPF/JAZ)	Assessment	Typical application
< 3.0	Inadequate	Old systems, poor design or controls
3.0–3.5	Acceptable	Older buildings with higher flow temperatures
3.5–4.0	Good	Standard new build
> 4.0	Very good	New build with underfloor heating, ground source

You will find detailed explanations of these figures and how to use them in Key Figures and Sizing of Heat Pumps.

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Choosing the right size

Correct sizing is crucial for efficiency and comfort. An oversized heat pump will cycle frequently (switching on and off), increasing wear and reducing efficiency.

Heat load as the basis

The design heat load is the heat output required at the lowest expected outdoor temperature. In Germany this is calculated to DIN EN 12831.

In the UK and Ireland, the equivalent is a room‑by‑room heat loss calculation carried out to BS EN 12831‑1 and related guidance (e.g. CIBSE guides in the UK, SEAI Domestic Technical Standards in Ireland).

Rule‑of‑thumb specific heat loads:

Building type	Specific heat load
Passive house	10–20 W/m²
Very efficient new build (e.g. UK Part L 2021 / NZEB in Ireland)	25–35 W/m²
Typical modern new build	40–50 W/m²
Post‑1995 retrofit with good insulation	60–80 W/m²
Pre‑1980 building, partially upgraded	100–150 W/m²
Older, largely uninsulated building	120–180 W/m²

Simple heat load formula

Heat load (kW) = Floor area (m²) × Specific value (W/m²) ÷ 1000

Example: A new build of 150 m² with 45 W/m² requires: 150 × 45 ÷ 1000 = 6.75 kW heat load

Allowance for domestic hot water

For domestic hot water (DHW) an allowance is added:

• Typical household: +0.25 kW per person
• If DHW is provided by a separate heat pump water heater: no allowance needed here

Complete example:

• 150 m² new build: 6.75 kW
• 4‑person household: +1.0 kW
• Total: 7.75 kW → choose an 8 kW heat pump

For a more precise calculation you can use our Heat Load Calculator.

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Operating modes

Different operating modes are used depending on the building and requirements.

Monovalent operation

The heat pump covers the entire heat demand on its own. This is usually the most efficient mode.

Prerequisites:

• Well‑insulated building (new build or thoroughly renovated)
• Low‑temperature heating system (max. approx. 55°C flow)
• Heat pump sized to the design heat load

Bivalent operation

The heat pump works together with a second heat source. Below a defined outdoor temperature (the bivalence point) the auxiliary heater switches on.

Variants:

Variant	Description
Bivalent‑parallel	Heat pump and auxiliary heater run together
Bivalent‑alternative	Below the bivalence point only the auxiliary heater runs
Bivalent‑part‑parallel	Combination of both strategies

Hybrid operation

A hybrid system combines a heat pump with a gas or oil boiler in one system. The controller automatically selects the most economical mode of operation based on outdoor temperature and energy prices.

Decision aid:

Situation	Recommended mode
New build with underfloor heating	Monovalent
Renovated building with low flow temperatures	Monovalent
Older building with radiators needing ~60°C	Bivalent or hybrid
Older building, no major fabric upgrades planned	Hybrid

You will find more detail in Operating Modes: Monovalent, Bivalent and Hybrid.

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Costs and economic performance

The costs of a heat pump system consist of purchase, installation and ongoing running costs.

Upfront costs (including installation)

Indicative ranges for typical homes:

Heat pump type	Cost	Comment
Air‑to‑water	10,000–20,000 €	Depending on output and manufacturer
Ground source (horizontal loop)	15,000–25,000 €	Including ground collector
Ground source (borehole)	18,000–35,000 €	Including drilling (approx. 80–120 €/m)
Water‑to‑water	15,000–30,000 €	Including well system

Calculating running costs

Annual electricity costs can be estimated with:

Electricity cost = Heat demand (kWh/year) ÷ Seasonal factor × Electricity price (€/kWh)

Example:

• Heat demand: 15,000 kWh/year
• Seasonal factor (SPF/JAZ): 4.0
• Electricity price: 0.30 €/kWh

Electricity cost = 15,000 ÷ 4.0 × 0.30 = 1,125 €/year

Comparison with fossil heating

Indicator	Heat pump	Gas condensing boiler	Oil condensing boiler
Energy price	0.30 €/kWh (electricity)	0.12 €/kWh	0.10 €/kWh
Seasonal efficiency / SPF	4.0	0.95	0.90
Effective cost per kWh heat	0.075 €/kWh	0.126 €/kWh	0.111 €/kWh
At 15,000 kWh/year	1,125 €/year	1,890 €/year	1,665 €/year

With a seasonal factor of 4.0, a heat pump has the lowest running costs, even though electricity is more expensive per kWh than gas or oil.

Incentives and grants (UK, Ireland & international)

In Germany, heat pumps are supported via BAFA and the BEG scheme. In the UK, Ireland and other countries, there are different but broadly comparable programmes.

United Kingdom (Great Britain):

• Boiler Upgrade Scheme (BUS)

  • Grants for low‑carbon heating in existing homes and some non‑domestic buildings in England and Wales.
  • Typical grant levels (2025/26 – check for updates):
  • £7,500 for air‑source heat pumps
  • £7,500 for ground source heat pumps
  • Requirements include:
  • Property in England or Wales
  • Replacing existing fossil fuel or direct electric heating
  • MCS‑certified installer and product
  • Valid EPC without outstanding loft or cavity wall insulation recommendations (with some exceptions)

• Home Energy Scotland grants and loans (Scotland)

  • Grants and interest‑free loans for heat pumps, insulation and other measures.
  • Typical support: several thousand pounds grant plus optional top‑up loan, subject to eligibility and property type.

• Northern Ireland

  • Support schemes change more frequently; at the time of writing, there is no direct equivalent to BUS, but occasional grant programmes and low‑interest loans may be available via local or UK‑wide schemes.

Ireland:

• SEAI Heat Pump System Grants
  • Grants for air‑to‑water, ground source and other heat pumps in existing homes.
  • Typical grant amounts (subject to change):
  • Up to €6,500 for ground source systems
  • Around €4,500–€6,500 for air‑to‑water systems, depending on dwelling type
  • Key conditions:
  • Home built before 2021
  • Technical assessment to confirm the building is heat‑pump‑ready (sufficient insulation and airtightness)
  • SEAI‑registered contractor and products.

Insulation and renovation support:

• UK: ECO4, Great British Insulation Scheme and various local authority schemes support insulation and other fabric measures, especially for low‑income households.
• Ireland: SEAI offers grants for attic, cavity wall, external wall and other insulation measures, as well as “One Stop Shop” deep retrofit supports.

Solar/PV and general efficiency:

• UK: Smart Export Guarantee (SEG) pays for exported PV electricity; some local grants or low‑interest finance for PV and batteries.
• Ireland: SEAI Solar PV grants for domestic systems (up to several thousand euros depending on system size).
• Many other countries offer tax credits, rebates or low‑interest loans for heat pumps, insulation and PV. Local regulations and funding levels vary significantly, so always check current national and regional programmes.

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Heat pumps in existing buildings

Installing a heat pump in an existing building is often possible but requires careful planning.

Typical challenges

• High flow temperatures: Older radiators may need 60–70°C to deliver enough heat.
• Poor insulation: High heat load requires a large heat pump and increases running costs.
• Space constraints: Finding a suitable location for the outdoor unit can be difficult in dense urban areas.

Possible solutions

Measure	Effect
Fabric insulation (walls, roof)	Reduces heat load by 30–50%
Window replacement	Reduces heat losses and draughts
High‑output/low‑temperature radiators	Allow 45–50°C flow temperatures
(Partial) underfloor heating	Further reduces required flow temperature
Hybrid system	Uses boiler support in very cold weather

Realistic seasonal performance in existing buildings

Building condition	Flow temperature	Expected SPF/JAZ
Largely uninsulated, old radiators	60–70°C	2.5–3.0
Partially renovated	50–55°C	3.0–3.5
Renovated, new radiators	45–50°C	3.5–4.0
Renovated, underfloor heating	35–40°C	4.0–4.5

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The dream team: heat pump + solar PV

Combining a heat pump with a photovoltaic (PV) system offers particular advantages: self‑generated solar electricity powers the heat pump, reducing running costs and improving the carbon footprint.

Synergies of the combination

• Increase self‑consumption: Surplus solar power is used by the heat pump.
• Cut electricity bills: Self‑generated electricity instead of paying the full retail tariff.
• Low‑carbon heating: Renewable electricity for heat.
• Greater independence: Reduced reliance on the grid and energy price volatility.

Sizing recommendations

Component	Sizing guideline	Example (150 m²)
Heat pump	Based on heat load	8 kW
PV system	Standard size + 2–3 kWp	10 kWp
Battery storage	Optional, 8–12 kWh	10 kWh

Example calculation

Starting point:

• 150 m² new build, 4 occupants
• 8 kW heat pump, seasonal factor 4.0
• Heat demand: 15,000 kWh/year → HP electricity: 3,750 kWh/year
• Household electricity: 4,000 kWh/year
• Total electricity demand: 7,750 kWh/year

With 10 kWp PV and 10 kWh battery:

• PV yield: approx. 10,000 kWh/year
• Self‑consumption: approx. 5,000 kWh/year (50%)
• Degree of self‑sufficiency: around 65%
• Grid import: only about 2,750 kWh/year
• Saving: roughly 1,500 €/year (depending on tariffs and export payments)

More on this combination can be found in Heat Pump Types and the Dream Team with Solar.

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Pros and cons at a glance

Advantages

Advantage	Explanation
High efficiency	Seasonal factors of 3–5: 1 kWh of electricity yields 3–5 kWh of heat
Environmentally friendly	No on‑site CO₂ emissions; very low carbon with renewable electricity
Low running costs	With good seasonal performance, cheaper than gas or oil per kWh of heat
Long service life	15–25 years, relatively low maintenance
No fuel storage	No oil tank, no gas connection required
Cooling capability	Many models can provide summer cooling
Grants available	Significant government support in the UK, Ireland and many other countries

Disadvantages

Disadvantage	Explanation
High upfront cost	10,000–35,000 € depending on type and building
Dependent on electricity	No heating during power cuts without backup
Efficiency in very cold weather	Air‑source units lose output and efficiency at very low temperatures
Noise	Outdoor units produce 35–50 dB(A); careful siting is important
Low flow temperatures needed	Not ideal for systems that require very high flow temperatures
Design effort	Careful sizing, hydraulic design and controls are essential

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Frequently asked questions (FAQ)

Is a heat pump worthwhile in an older building?

Yes, under certain conditions. The key factors are the achievable flow temperature and the building’s heat load. If flow temperatures below about 55°C are possible and a seasonal factor of at least around 3.0 can be achieved, a heat pump is usually economically sensible. Where high flow temperatures remain necessary, a hybrid system (heat pump plus boiler) can be the better choice.

How loud is a heat pump?

Modern air‑to‑water heat pumps typically have sound power levels of around 35–55 dB(A). For comparison: a fridge is about 40 dB(A), normal conversation around 60 dB(A). Local planning rules in the UK and Ireland set limits on noise at neighbouring properties, so the outdoor unit should be sited with adequate distance from boundaries and bedrooms, and vibration‑damping mounts should be used.

How long does a heat pump last?

With regular maintenance, the service life is typically 15–25 years. The compressor is the component most subject to wear. Frequent cycling (on/off operation) shortens its life, which is why correct sizing and good control strategies are important.

What is the optimal flow temperature?

The lower the better for efficiency. Typical guide values:

• Underfloor heating: 30–35°C
• Low‑temperature radiators: 45–50°C
• Conventional radiators: 55–60°C

Every 5°C reduction in flow temperature increases the seasonal performance factor by roughly 0.3–0.5 points.

Can a heat pump also cool?

Many heat pumps are reversible and can provide cooling in summer. Air‑to‑water heat pumps offer active cooling via the heating circuit, while ground source systems can often provide passive cooling using the ground as a heat sink. Cooling capacity is limited and does not fully replace a dedicated air‑conditioning system, but it can significantly improve comfort.

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Building standards, regulations and energy labels (UK, Ireland & international)

In the original German context, heat pump design and building performance are linked to DIN and VDI standards and the German building energy code. In the UK, Ireland and internationally, there are different but comparable frameworks.

Key standards and norms:

• Heat load and U‑values:

  • EN ISO 6946 (thermal resistance and U‑value calculation) is implemented in the UK and Ireland via national building regulations and guidance (e.g. SAP and SBEM in the UK, DEAP in Ireland).
  • Heat loss calculations for heating design are based on BS EN 12831‑1 (UK & Ireland equivalent to DIN EN 12831).

• Heat pump performance and testing:

  • BS EN 14511 – testing and rating of air conditioners, liquid chilling packages and heat pumps.
  • BS EN 14825 – seasonal efficiency (SCOP/SEER) for space heating and cooling.
  • In the UK, MCS standards (e.g. MIS 3005 for heat pumps) set design and installation requirements.
  • In Ireland, SEAI technical standards and HARP database requirements apply.

• Building energy performance regulations:

  • United Kingdom:
  • England: Building Regulations Part L 2021 (Conservation of fuel and power) with SAP 10 methodology.
  • Scotland: Section 6 (Energy) of the Scottish Building Standards.
  • Wales and Northern Ireland have their own Part L equivalents.
  • Ireland:
  • Building Regulations Part L and the NZEB (Nearly Zero Energy Building) requirements for new dwellings.
  • Internationally, many countries implement the EU Energy Performance of Buildings Directive (EPBD) or similar national codes.

Energy labels and certificates:

• EU/UK product energy labels:

  • Heat pumps sold in the EU and UK carry an energy label based on EN 14825, showing SCOP, efficiency class (A+++ to G) and noise data.

• Building energy performance certificates:

  • UK: Energy Performance Certificates (EPCs) are required when selling or letting properties and for new builds. They are based on SAP or SBEM calculations.
  • Ireland: Building Energy Rating (BER) certificates are mandatory for sale, rent and new construction, based on DEAP.
  • Many other countries have similar EPC/BER systems, though rating scales and methodologies differ.

Minimum U‑values, airtightness requirements and renewable energy obligations vary between jurisdictions and are updated regularly. As a rule, new buildings in the UK and Ireland must meet stringent fabric standards and often incorporate low‑carbon heating such as heat pumps to comply with Part L/NZEB requirements.

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Conclusion

The choice of the right heat pump type depends on the building, the plot and the available budget. Air‑to‑water heat pumps offer the best compromise between cost and efficiency for most homes, while ground source systems achieve the highest efficiencies where sufficient space and budget are available.

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The complete “Heat Pumps” article series

1. Heat Pumps: The Complete Guide – you are here
2. The Anti‑Fridge: How Does a Heat Pump Work? – physical principles
3. Components: Heat Exchangers, Compressor and Expansion Valve – components in detail
4. Key Figures and Sizing of Heat Pumps – COP, seasonal factors, SCOP
5. Operating Modes: Monovalent, Bivalent and Hybrid – operating strategies explained
6. Heat Pump Types and the Dream Team with Solar – types & combination with PV

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Sources

• DESTATIS: Heat Pumps in New Buildings 2023
• UK Government: Boiler Upgrade Scheme and Building Regulations Part L (official gov.uk guidance)
• SEAI (Ireland): Heat Pump System Grants and Domestic Technical Standards
• BS EN 14511: Air conditioners, liquid chilling packages and heat pumps – Testing and rating
• BS EN 14825: Seasonal energy efficiency of space heating and cooling
• EN ISO 6946: Building components and building elements – Thermal resistance and thermal transmittance
• Mordor Intelligence: Heat Pumps Market Report

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Calculate your seasonal performance now

Use our free heat pump calculator to estimate the seasonal performance factor of your heat pump – including running costs and CO₂ balance.

→ Go to the Heat Pump Calculator