Air Source Heat Pumps: A Comprehensive Overview

Air Source Heat Pumps (ASHPs) are a revolutionary solution for heating homes, offering warmth and an environmentally conscious approach. Understanding sustainable heating options becomes paramount as we navigate the challenges of climate change.

In this discussion, we’ll unravel the mechanics behind ASHPs, their eco-friendly advantages, and their increasing relevance in fostering a greener way of life, particularly within the UK’s diverse landscape.

This article discusses science, benefits, installation, and other essential aspects of ASHPs.

Air Source Heat Pumps: A Comprehensive Overview

What is an Air Source Heat Pump?

An Air Source Heat Pump (ASHP) is a device that uses the outside air to heat or cool a building. Think of it as a kind of “reverse refrigerator.” Instead of creating cold air inside and releasing hot air outside (like a fridge does).

The ASHP takes the heat from outside and brings it inside to warm up a space. It can also work the other way around, extracting heat from inside to cool a building. It makes ASHPs an energy-efficient and eco-friendly way to control the temperature.

Types of Air Source Heat Pumps

Air Source Heat Pumps (ASHPs) have revolutionized our thoughts on heating systems. Among the various configurations available, the Air-to-Air and Air-to-Water systems are popular choices, each with unique advantages and applications. Here’s a detailed breakdown of both:

1. Air-to-Air Heat Pumps


As the name suggests, air-to-air heat pumps transfer heat from the outside air directly into the indoor air of a building.

Key Features:

Fans: These pumps employ fans to circulate the warm air throughout the rooms.

Quick Response: They often provide rapid heating or cooling, making them ideal for spaces requiring immediate temperature adjustments.

No Central Heating System Needed: Unlike Air-to-Water systems, Air-to-Air pumps don’t require a wet central heating system, simplifying installation in some cases.


Efficiency: They can quickly adjust the indoor temperature, saving energy.

Versatility: Suitable for both heating and cooling purposes.

Simplicity: Typically easier and less expensive to install in homes without central heating systems.

2. Air-to-Water Heat Pumps


Air-to-water heat pumps extract heat from the outside air and transfer it to a water-based system, such as underfloor heating or radiators.

Key Features:

Distribution System: They work in tandem with wet central heating systems.

Consistent Temperature: Once the water reaches the desired temperature, it circulates through the heating system, providing consistent warmth across different rooms.

Hot Water Production: Many air-to-water systems can also produce hot water for domestic use.


Uniform Heating: Ideal for more significant properties or buildings with multiple rooms, ensuring even heat distribution.

Integration with Existing Systems: They can often be integrated with existing radiators or underfloor heating systems, making them a feasible choice for renovations.

Energy Efficiency: By leveraging the heat from the air, they offer a more sustainable and potentially cost-effective heating solution.

Read more about How to Obtain Air Source Heat Pump.

Science Behind Air Source Heat Pump

Air Source Heat Pumps (ASHPs) are fascinating devices that effectively capture and utilize the heat present in the surrounding air. Their functionality is grounded in scientific principles, which, when understood, offer insights into their efficiency and reliability. Here’s a detailed look at the science behind ASHPs:

  1. The Principle of Heat Exchange:

At the heart of an ASHP is the process of heat exchange. Even when the outside air feels cold, it still contains thermal energy, albeit in a dispersed form. ASHPs tap into this latent heat energy.

  1. The Role of Refrigerant:

A central component in the operation of ASHPs is the refrigerant—a special fluid with properties that allow it to change states at relatively low temperatures. The refrigerant circulates through the system, transitioning between liquid and gaseous states.

  1. The Evaporation Process:

When the refrigerant first enters the outdoor unit of the ASHP, it is in a liquid state. As it encounters the cold ambient air, it absorbs the available heat. This absorption causes the refrigerant to evaporate, transforming it from a liquid into a low-temperature gas.

  1. Compression and Temperature Increase:

Now laden with absorbed heat, the gaseous refrigerant is directed into the ASHP’s compressor. Here, it undergoes compression, which significantly increases its temperature. This process is fundamental to the pump’s efficiency because raising the temperature of the refrigerant to a usable level ensures effective heating indoors.

  1. Heat Release Indoors:

The now-hot refrigerant gas, which has absorbed heat from the outside and been further heated through compression, is passed through a condenser coil inside the building. As indoor air passes over this coil, the heat from the refrigerant is released into the space, warming it up. This mechanism is akin to how a central heating system operates but with the added advantage of extracting external heat.

  1. Recirculation and Repetition:

After releasing its heat indoors, the refrigerant reverts to a liquid state. It then returns to the outdoor unit, starting the cycle anew. This continuous process ensures a consistent supply of warmth inside, even as the external temperature fluctuates.

Components of Air Source Heat Pump System

Components of Air Source Heat Pump System

Components of Air Source Heat Pump System

Air Source Heat Pump (ASHP) systems are intricately designed assemblies incorporating various components to ensure efficient heat transfer and distribution.

1. Outdoor Unit:

Compressor: Often termed the heart of the ASHP, the compressor plays a pivotal role in the system’s operation. Its primary function is to compress the low-temperature, low-pressure refrigerant vapor, significantly increasing its temperature and pressure. This high-pressure, high-temperature gas is then ready for heat exchange.

Heat Exchanger (Condenser Coil): Positioned within the outdoor unit, the heat exchanger facilitates the transfer of heat from the refrigerant to the outside air. As the hot, pressurized refrigerant gas flows through the coil, it releases its heat to the colder ambient air, causing the refrigerant to condense back into a liquid state.

2. Indoor Unit:

Indoor Heat Exchanger (Evaporator Coil): This component serves as the counterpart to the outdoor heat exchanger. After the refrigerant has been compressed and heated outdoors, it enters the indoor unit’s evaporator coil as a high-pressure, high-temperature liquid. As the refrigerant expands and evaporates within the coil, it absorbs heat from the indoor air, cooling the surrounding space.

Fan: Integral to the indoor unit, the fan circulates air over the evaporator coil. This airflow ensures that the heat absorbed by the refrigerant is effectively distributed throughout the room or building, maintaining a consistent temperature.

3. Refrigerant:

Role in Heat Transfer: The refrigerant is the medium through which heat is transferred within the ASHP system. Its unique properties allow it to change states (from liquid to gas and back) at relatively low temperatures, facilitating efficient heat exchange processes.

Circulation Path: The refrigerant follows a closed-loop pathway, cycling continuously between the outdoor and indoor units. As it moves through the system, it undergoes phase changes and temperature variations, ensuring the consistent extraction and release of heat.

Benefits of Air Source Heat Pumps

Air Source Heat Pumps (ASHPs) have garnered attention for their multifaceted advantages in modern heating and cooling applications.

  1. Energy Efficiency: ASHPs can produce more energy than they consume, reducing energy bills.
  2. Versatility: They can provide both heating and cooling solutions.
  3. Low Maintenance: Fewer moving parts mean less wear and tear.
  4. Reduced Carbon Footprint: Using renewable heat, ASHPs contribute to lower greenhouse gas emissions.

Installation and Maintenance of Air Source Heat Pumps

Installation and Maintenance of Air Source Heat Pumps

Air Source Heat Pumps (ASHPs) represent a blend of sophisticated technology and environmental conscientiousness. Here’s a detailed exploration of the installation process and essential maintenance practices for ASHPs:

1. Importance of Professional Installation:

The standard installation of ASHPs is a complex DIY task. Given the intricate components and precise calibration required, it’s imperative to enlist the expertise of certified professionals. Professionals possess the requisite training and experience to:

Ensure Correct Sizing: Determining the suitable capacity is crucial. Oversized or undersized units can compromise efficiency and longevity.

Optimize Placement: Proper positioning away from obstructions and in conducive environments can enhance performance and minimize wear.

Ensure Safe Installation: Adherence to safety protocols during installation is paramount, safeguarding the system’s integrity and the property.

2. Regular Maintenance Essentials:

Refrigerant Levels: The refrigerant plays a pivotal role in the heat exchange.  Periodic checks, ideally by professionals, ensure optimal levels, preventing inefficiencies or system malfunctions.

Cleaning Filters: The efficiency of ASHPs can be significantly hampered by clogged or dirty filters. Regular inspection and cleaning or replacement of filters ensure unobstructed airflow, promoting optimal heat exchange and reducing strain on the system.

Inspecting Coils and Fans:Dust, debris, or other contaminants can accumulate on the coils and fans, impeding their function. Regular inspections and cleaning sessions can prevent such build-ups, ensuring consistent performance.

Checking Electrical Components: Electrical energy connections, controls, and other related components should be inspected for wear, corrosion, or potential faults. Addressing any issues promptly can prevent larger, more costly problems.

3. Scheduled Professional Maintenance:

While homeowners can undertake some maintenance tasks, scheduling periodic professional inspections is invaluable. Professionals possess the expertise to detect underlying issues, calibrate the system for optimal performance, and provide recommendations tailored to prolong the ASHP’s lifespan and maximize its efficiency.

Air Source Heat Pump Efficiency

Due to advanced technologies, modern air source heat pumps (ASHPs) excel in diverse climates, functioning efficiently even at -15 °C. Key factors for optimal efficiency include regular maintenance to ensure clean coils and proper refrigerant levels. Additionally, selecting the right-sized unit tailored to specific space needs ensures peak performance and energy savings.

Environmental Impact of Air Source Heat Pumps

Environmental Impact of Air Source Heat Pumps

Air Source Heat Pumps (ASHPs) play a pivotal role in promoting environmental sustainability. Their impact can be dissected into several key facets:

1. Reduction in Fossil Fuel Dependency:

Transitioning from Fossil Fuels: ASHPs operate by harnessing heat from the ambient air, eliminating the need for traditional heating systems that rely on burning fossil fuels like coal or natural gas.

Direct Carbon Emission Reduction: By substituting fossil fuel-based heating methods, ASHPs directly contribute to a decrease in carbon emissions associated with heating processes.

2. Alignment with Climate Change Initiative:

Global Efforts and ASHPs: The deployment of ASHPs resonates with international initiatives aimed at reducing greenhouse gas emissions and mitigating the impacts of climate change.

Promoting Sustainable Practices: As ASHPs become more prevalent, they foster a broader shift towards sustainable heating solutions, reinforcing a collective commitment to environmental stewardship.

Compatibility with UK Climate

Compatibility of Air Source Heat Pumps with the UK Climate

The UK’s temperate climate presents specific challenges and opportunities for heating technologies. Air Source Heat Pumps (ASHPs) have emerged as a fitting solution for this environment, and their compatibility can be analyzed through several lenses:

1. Climate Suitability:

Temperate Characteristics: The UK’s climate is characterized by mild summers and cool winters. ASHPs are designed to extract heat from ambient air, making them particularly effective in such temperate conditions.

Operational Range: Advanced ASHP models are engineered to function efficiently even when temperatures drop, ensuring consistent performance throughout the varying UK seasons.

2. Technological Advancements:

Enhanced Cold Weather Performance: Recognizing the UK’s occasional colder spells, technological innovations in ASHPs have bolstered their capacity to operate optimally in sub-zero temperatures.

Efficiency Optimizations: Continuous research and development have refined ASHP designs, enhancing their overall efficiency and reliability, especially in regions with temperate climates like the UK.

Cost Savings with Air Source Heat Pumps

Air Source Heat Pumps can be expensive to buy and install. However, they offer significant long-term savings on energy bills.

For instance, the UK government’s ECO4 scheme suggests that homeowners can save an average of £570 per year on an air source heat pump cost with an ASHP. These pumps also act as a buffer against rising energy prices. Furthermore, the UK’s ECO4 Scheme provides financial incentives to encourage more people to adopt ASHPs.

ASHP under ECO4 Scheme 

The UK’s Energy Company Obligation (ECO4) Scheme is a fantastic initiative to tackle rising energy costs and carbon emissions. It promotes installing energy-efficient heating systems, including Air Source Heat Pumps (ASHPs), by offering substantial financial incentives to homeowners and businesses.

Let’s delve deeper into how the ECO4 Scheme can help you reap the benefits of ASHPs:

Financial Incentives:

Grants: ECO4 provides valuable grants to eligible households to install ASHPs. The exact amount you receive depends on various factors like your household income and energy efficiency band.

Reduced Bills: ASHPs are notoriously energy-efficient, extracting heat from the air rather than relying on fossil fuels. This translates to dramatically lower heating bills than traditional gas boilers, especially in the face of rising energy costs. Studies estimate average annual savings of £570 on heating bills through ECO4-funded ASHP installations.

Environmental Benefits:

Reduced Carbon Footprint: ASHPs play a crucial role in decarbonizing the heating sector. By switching to clean, renewable energy from the air, you significantly reduce your reliance on fossil fuels and decrease your household’s carbon emissions. This contributes to cleaner air, improved public health, and tackling climate change.

Energy Independence: The growing dependence on imported fossil fuels makes energy security a national concern. By utilizing an abundant and locally available energy source like air, ASHPs promote energy independence and reduce reliance on volatile global markets.

Eligibility and Steps to Take:

  • Homeowners and businesses in England, Scotland, or Wales with energy efficiency ratings D-G are eligible for ECO4 support.
  • You can check your eligibility and potential grant amount through our website or by contacting us.

ASHP Frequently Asked Question

Does Air Source Heat Pump Cooling Work?

Yes, they can work in reverse to provide cooling during warmer months.

How noisy are they? 

Modern units are designed to operate quietly, but placement and installation quality can impact noise levels.

How will S6 Energy Assist you in Obtaining an ASHP under the ECHO Scheme?

S6 Energy is here to assist you in acquiring an Air Source Heat Pump (ASHP) under the ECHO Scheme. We leverage our expertise and industry connections to guide you through the application process, ensuring all eligibility criteria are met. With our support, you can confidently navigate the complexities of the scheme and make a seamless transition to sustainable heating solutions.

Check your eligibility today with S6 Energy.

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