Insulation and Air Source Heat Pumps - Heat IQ

Air Source Heat Pumps (ASHPs) are increasingly becoming a preferred choice for sustainable home heating in the UK. These systems, known for efficiently transferring heat from outside air into homes, represent a significant shift towards eco-friendly heating solutions. However, the efficiency of ASHPs is not solely dependent on the technology itself; it is also significantly influenced by the insulation of the home in which they are installed.

The effectiveness of an ASHP is greatly enhanced in a well-insulated home. Proper insulation reduces the heat lost from the property, ensuring the heat pump operates optimally. This improves the system’s efficiency and contributes to substantial energy savings and a reduced carbon footprint.


Air Source Heat Pumps and Efficiency

Air Source Heat Pumps (ASHPs) are a modern solution for heating and cooling homes. They operate by extracting heat from the air outside, even in cold temperatures, and using it to warm the interior of a building. An ASHP absorbs heat from the outside environment, compresses it to increase its temperature, and then releases it inside the home. This process is highly efficient because it transfers heat rather than generates it directly, making ASHPs a more environmentally friendly option than traditional heating systems.

The efficiency of an ASHP is closely linked to the insulation quality of the home where it is installed. Good insulation reduces heat loss, meaning that once the ASHP heats the home, that warmth is retained for longer periods. In an inadequately insulated house, the ASHP must work harder to maintain a consistent temperature, as heat is rapidly lost through walls, roofs, and windows. This increases energy consumption and can strain the heat pump, potentially reducing its lifespan.

Effective insulation, therefore, enhances the efficiency of an ASHP in two key ways:

1. Lower Energy Usage:
With reduced heat loss, the ASHP doesn’t need to operate as frequently or as long to maintain the desired temperature, leading to lower energy consumption.

2. Consistent Performance:
A well-insulated home allows the ASHP to maintain a steady and efficient performance, providing a comfortable indoor environment without overburdening the system.


Loft Insulation

Loft insulation is a critical aspect of home insulation, particularly when optimising the efficiency of an Air Source Heat Pump (ASHP). Heat rises, and without proper insulation in the loft or attic, a significant portion of the warmth generated by the ASHP can escape. This leads to higher energy usage and reduced overall efficiency. Homeowners can significantly reduce heat loss by insulating the loft, ensuring the ASHP operates more effectively and economically.

The recommended depth for mineral wool insulation, one of the most common materials used for loft insulation, is at least 270mm. This thickness is considered sufficient to provide optimal thermal resistance, slowing the movement of heat out of the home and thus maintaining a consistent and comfortable temperature indoors.

Installing loft insulation can be a feasible DIY project for many homeowners, offering a cost-effective way to enhance home energy efficiency. The cost of materials, such as rolls of mineral wool insulation, is relatively low, averaging around £6 per square metre. However, for those preferring professional installation, the cost can rise to approximately £11 – £15 per square metre. The decision between DIY and professional installation can be based on personal comfort with home improvement tasks, the complexity of the loft space, and budget considerations.

Two main methods of insulating a loft are between the joists or under the rafters.

Insulating the Joists:
This method involves laying insulation between the joists and the horizontal beams that make up the loft floor. Insulating between the joists effectively prevents heat from rising from the living spaces below. However, this method means the loft space will not be insulated; therefore, it might become colder, which is a consideration if the loft is used for storage.

Insulating the Rafters:
Insulating under the rafters, the sloped beams supporting the roof create a warm loft. This method involves fitting insulation material directly under the roof. It’s a preferable approach if the loft is used as a living space or if homeowners want to maintain a more uniform temperature throughout the house.


Wall Insulation

For homes built with cavity walls, typical in constructions post-1935, cavity wall insulation is crucial in enhancing heating efficiency. A cavity wall consists of two rows of brick or concrete blocks with a hollow space or ‘cavity’ between them. Insulating this cavity is a crucial strategy in preventing heat loss from the home.

Installing cavity wall insulation is a specialised task that requires professional expertise. It involves injecting insulating material into the cavity through drilled holes in the external walls. This process requires specific tools and an understanding of the building structure to ensure the insulation is evenly distributed without damaging the wall’s integrity. The precision and expertise of professional installers are essential to ensure the insulation performs as intended and benefits the overall efficiency of an Air Source Heat Pump system.

For homes with solid walls, which lack the cavity space, insulation options are slightly different and can be more costly. Solid wall insulation can be applied either internally or externally:

Internal Wall Insulation:
This involves fitting rigid insulation boards to the wall or building a stud wall filled with insulating material. While less expensive than external insulation, this method can slightly reduce the interior space of rooms.

External Wall Insulation:
This method involves fixing insulating material to the outside walls and covering it with cladding or render. External insulation is more expensive but can improve the appearance of the building and does not affect the internal living space.

The costs for solid wall insulation vary, but they are generally higher than cavity wall insulation due to the more extensive materials and labour involved.

Wall insulation provides substantial benefits throughout the year, whether in cavity or solid walls. In winter, it helps retain heat within the home, enhancing the efficiency of heating systems like ASHPs. Conversely, in summer, well-insulated walls can keep excessive heat out, maintaining a cooler and more comfortable indoor environment. This dual benefit makes wall insulation a crucial factor in creating an energy-efficient home that maximises the potential of modern heating solutions like ASHPs.


Double Glazing

Double glazed windows play a significant role in enhancing the thermal efficiency of homes, an aspect that is particularly relevant when optimising the performance of Air Source Heat Pumps (ASHPs). These windows are made up of two panes of glass with a gap in between, usually filled with an inert gas like argon. This design creates an insulating barrier that reduces heat transfer, effectively retaining warmth inside the home during colder months and keeping heat out during warmer periods.

The Energy Saving Trust has highlighted the potential savings from installing double glazing. According to their findings, an average household can save between £105 and £155 per year on heating costs by switching to double-glazed windows. These savings are a direct result of the increased insulation provided by double glazing, which reduces the need for excessive heating and, consequently, lowers energy consumption.

While the primary advantage of double glazing is its contribution to heat retention and energy savings, it offers several other benefits:

Enhanced Security:
Double-glazed windows are typically more secure than single-pane windows. Their robust construction makes them harder to break, providing an added layer of security to homes.

Reduced Condensation:
A common issue in homes with poor insulation is condensation, leading to mould and damp problems. Double glazing reduces the risk of condensation as the inner pane of glass is kept at a more consistent and warmer temperature.

Noise Reduction:
For those living in noisy areas, double-glazed windows can significantly reduce the amount of external noise that enters the home. This is due to the vacuum or gas-filled space between the two panes of glass, which acts as a sound barrier.

Temperature Regulation:
Besides keeping the home warm in winter, double glazing helps maintain a cooler environment during hot weather. Reducing the amount of heat entering the home can contribute to a more comfortable living space in the summer months.



In pursuing energy efficiency through insulation and double glazing, it’s crucial not to overlook the importance of adequate ventilation in homes. While well-insulated homes and Air Source Heat Pumps (ASHPs) effectively retain heat, they can also trap moisture and stale air, leading to dampness and poor indoor air quality. Proper ventilation ensures a healthy living environment by circulating fresh air and removing excess moisture.

Maintaining a balance between heat retention and air quality involves strategic ventilation that does not compromise the home’s energy efficiency. Here are some methods to achieve this balance:

Controlled Natural Ventilation

Trickle Vents:
Installing trickle vents in windows is a simple and effective way to allow continuous air exchange. These small vents can be adjusted to control airflow and are designed to minimise heat loss.

Ventilation Grilles:
In areas like kitchens and bathrooms with higher moisture levels, fitting ventilation grilles can help expel damp air.

Mechanical Ventilation Systems

Extractor Fans:
These are particularly useful in rooms with high humidity levels. Modern extractor fans are energy-efficient and can operate automatically when moisture is detected.

Mechanical Ventilation with Heat Recovery (MVHR):
An MVHR system can be a highly effective solution in very well-insulated homes. It extracts warm, stale air to heat fresh air from outside. This maintains good air quality and recovers heat, enhancing overall energy efficiency.

Ventilation Habits

Regular Opening of Windows:
Regularly opening windows, especially in rooms like the kitchen or bathroom after use, can significantly improve air quality.

Ventilation During and After Showers or Cooking:
Ensuring adequate ventilation during activities that produce a lot of steam can prevent condensation and moisture buildup.


The Combined Effect on ASHP Performance

The overall efficiency and effectiveness of Air Source Heat Pumps (ASHPs) are significantly influenced by two key factors: insulation and ventilation. Proper insulation in a home ensures minimal heat loss, so the ASHP doesn’t have to work as hard to maintain a comfortable indoor temperature. This directly impacts the energy consumption of the ASHP, leading to more efficient operation.

Ventilation, on the other hand, while crucial for maintaining air quality, can potentially lead to heat loss if not managed correctly. However, when balanced effectively with insulation, it ensures that while fresh air is circulated, the heat generated by the ASHP is not wasted. Modern ventilation systems, especially those with heat recovery capabilities, complement the function of ASHPs by retaining most of the heat that would otherwise be lost in the ventilation process.

In a well-insulated home with optimised ventilation, an ASHP can achieve its full potential in terms of energy efficiency, leading to significant cost savings over time. Here’s how:

Reduced Energy Consumption:
Since the ASHP does not have to compensate for heat loss due to poor insulation or excessive ventilation, it uses less energy to heat the home. This reduced energy consumption is directly reflected in lower utility bills.

Consistent Performance:
With the minimisation of heat loss, the ASHP can operate more consistently at optimal efficiency. This not only ensures a comfortable living environment but also contributes to the longevity and reduced maintenance of the system.

Maximised Savings over Time:
While the initial costs for installing an ASHP and upgrading insulation and ventilation may be significant, the long-term savings in energy costs make this a cost-effective investment. Over time, the savings in energy bills can outweigh the initial outlay, making the ASHP a financially viable and sustainable heating solution.

The synergy between effective insulation, well-managed ventilation, and an ASHP can transform a home into an energy-efficient haven. By focusing on these aspects, homeowners can significantly enhance the performance of their ASHPs, resulting in a comfortable, healthy, and cost-effective living environment. This integrated approach is critical to realising the full benefits of an Air Source Heat Pump system.


Related Articles