The UK Overheating Crisis: Why Traditional British Homes Trap Heat and Need Climate Adaptation

Extreme heat is now more than just an occasional comfort issue for UK households.

The UK Health Security Agency estimates that 1,504 deaths were associated with five heat episodes in England during summer 2025. These figures estimate mortality associated with heat episodes. They do not represent a count of death certificates that specifically recorded heat exhaustion.

This situation is only accelerating as our climate changes.

Recent estimates from the UK Health Security Agency (UKHSA) reveal that 2,877 deaths were linked to hot weather during just two heatwaves in May and June of 2026.

To put this into perspective, this early 2026 figure is almost double the 1,504 heat-associated deaths recorded across a three-month period in 2025, putting the UK on track to surpass its highest annual record.

With periods of hot weather expected to become longer, more frequent, and more extreme, protecting vulnerable individuals from soaring indoor temperatures is no longer just about comfort—it is a critical health priority that reduces the severe pressures facing the NHS.

It is now clear that being exposed to long periods of high temperatures can have serious consequences.

According to the English Housing Survey, approximately three million English homes were reported to be overheating in 2024. Owner-occupied homes were slightly more likely to be reported as overheating than private or social rented homes.

For generations, British homes were mainly designed to retain warmth during cold, damp winters. Today, those same properties must also cope with warmer summers, strong solar gain and hot conditions that can continue for several days.

This has led parts of the British press to describe overheating homes as a “heat trap”. The phrase captures how some properties remain hot even after outdoor temperatures begin to fall, but the underlying problem is more complex.

To understand why UK houses get so hot in summer, we need to examine how heat enters the property, where it is stored and whether the building can release it effectively.

Why Do UK Houses Get So Hot In Summer?

A house does not become uncomfortably hot because of one material or design feature.

Overheating happens when more heat enters or is generated inside the home than can escape. The longer this goes on, the more heat builds up inside.

Common sources include:

• Direct sunlight passing through windows
• Heat entering through roofs, walls and open windows
• Occupants and pets
• Cooking and hot-water use
• Computers, televisions and other electrical equipment
• Artificial lighting
• Warm air entering through ventilation and air leakage

The building’s structure can absorb some of this heat.

Simply put, the building fabric is the outer shell of the home, including its walls, floors, roof, windows, and doors. Materials like brick, concrete, and stone can soak up heat during the day and slowly release it later.

Historic England refers to this ability to absorb, store and release heat as thermal mass.

If evenings stay warm, the home might not have enough time to release the stored heat before it gets hot again the next day.

Does Insulation Make UK Homes Overheat?

Some people blame insulation for making homes too hot in summer, but the situation is more complex.

Insulation slows the movement of heat through the building envelope. During winter, it helps retain warmth. In summer, it can also slow the transfer of heat from outdoors through walls and roofs.

The problem starts once heat gets inside the home.

Heat can enter through unshaded windows while people, appliances and cooking add even more warmth indoors. Insulation may then slow the rate at which that accumulated heat escapes.

This does not mean that insulation is inherently responsible for overheating. A well-insulated home with suitable shading, ventilation and cooling controls can perform well during both winter and summer.

Problems are more likely when a property combines good heat retention with:

• Large areas of unshaded glazing
• Limited cross-ventilation
• Windows that cannot be opened fully
• High internal heat gains

A home designed solely for winter warmth may perform well in cold weather but struggle in prolonged summer heat.

How Thermal Mass Affects Victorian Homes

Many Victorian terraced and semi-detached homes contain large areas of solid brickwork.

These heavy materials have thermal mass, which means they absorb, store and later release heat. This can help stabilise indoor temperatures during a short warm spell by slowing rapid changes.

During a prolonged heatwave, however, the walls may continue absorbing energy over several days. The stored heat can then be released back indoors during the evening and overnight.

If outdoor temperatures remain high, the property has little opportunity to cool before the next day begins. Bedrooms may therefore remain uncomfortable long after sunset.

Other overheating risks in older homes include:

• Loft rooms directly beneath the roof
• Narrow layouts with limited airflow
• Dark roofing exposed to direct sunlight
• Ventilation restricted by later renovations
• Extensions with large glazed doors or roof lights
• Internal rooms without direct access to outside air

Victorian homes can therefore retain unwanted summer heat, even if it feels draughty and difficult to warm in winter.

Why Modern New Builds Can Also Overheat

Older homes are not the only ones affected by overheating in the UK.

Modern houses and flats are often designed to reduce uncontrolled air leakage and unwanted heat loss. Building regulations also require suitable ventilation, while newer homes in England must consider overheating in line with Approved Document O.

These features can greatly lower heating needs. But homes still need an effective way to control sunlight and reduce heat in summer.

Modern overheating risks may include:

• Large south-facing or west-facing windows
• Limited external shading
• Highly glazed balconies and living areas
• Restricted window openings in upper-floor flats
• Internal corridors with poor airflow
• Heat generated by communal systems or neighbouring properties
• Mechanical ventilation that is not designed to provide active cooling
• Bedrooms positioned immediately beneath the roof

Flats can face particular challenges because occupants may be unable to create cross-ventilation or safely leave windows open overnight.

The problem is not that modern homes are too efficient. Instead, we need to think about both winter efficiency and summer comfort together.

What Is A Home’s Cooling Load?

Jargon Buster: Cooling Load
The total amount of heat energy that must be removed from an indoor space to maintain a comfortable temperature, factoring in elements like room dimensions, insulation, windows, and internal heat sources.

A cooling load is the amount of heat that must be removed from a space to maintain the desired indoor temperature.

It is not just about the size of the room.

Two bedrooms of the same size can require very different levels of cooling depending on their orientation, construction and use.

An experienced air-conditioning installer or HVAC engineer will assess the room’s cooling load before recommending a system.

This may involve considering:

• Room dimensions and ceiling height
• Window size and orientation
• Glazing type
• Roof and wall construction
• Insulation levels
• Occupancy
• Lighting and electrical equipment
• Ventilation
• Typical outdoor temperatures
• The preferred indoor temperature

These factors help determine the cooling capacity required for reliable and efficient performance.

If an air conditioner is too small, it may run constantly without adequately cooling the room. An oversized unit may cool the space too quickly, causing frequent on-and-off cycling and poor humidity control.

Getting the size right supports more consistent comfort, better efficiency and a longer system lifespan.

When Fixed Air Conditioning Becomes More Than a Luxury

Fans and portable air conditioners can provide temporary relief, but they do not always solve the underlying overheating problem.

A fan moves air across the skin, helping people feel cooler without removing heat from the room. The walls, ceiling, furniture, and surrounding air remain warm, so the accumulated heat persists even after the fan is switched off.

Portable air conditioners go a step further by extracting heat from a single room. However, many domestic models rely on a single exhaust hose fitted through a partially open or temporarily sealed window.

As indoor air is pushed outside, warmer air may be drawn back into the property through gaps around windows, doors and other openings. The compressor also remains inside the room, adding noise and taking up floor space.

Other limitations may include:

• A suitable window opening and temporary seal are required
• The exhaust hose can release heat back into the room
• Condensate may need to be drained or emptied
• One unit generally cools only one room
• The appliance must be moved or stored when not in use

Fans remain affordable, while portable air conditioners can be useful for tenants, for occasional cooling, or for properties where permanent installation is not possible.

However, when a home overheats repeatedly, temporary measures can become less practical. Bringing out the same equipment every summer does not address how the property will cope with longer and more frequent periods of heat.

A fixed split-system air conditioner provides a permanent solution for removing indoor heat. It transfers that heat outside through a closed refrigerant circuit, with the compressor positioned outdoors. This allows the system to provide quieter and more consistent cooling without relying on an open-window exhaust hose.

For some properties, fixed air conditioning may therefore become more than a luxury. It can form part of the building’s essential cooling infrastructure, particularly where passive measures cannot maintain a comfortable indoor temperature.

This may apply to:

• Loft conversions
• Top-floor flats
• Bedrooms with large west-facing windows
• Homes where noise or security limits window use
• Rooms containing heat-producing equipment
• Properties with limited opportunities for external shading

Not every home will require mechanical cooling. Shading, ventilation and reduced solar gain should still form part of the wider strategy.

However, where these measures cannot prevent repeated overheating, a fixed system may provide the reliable cooling the property needs rather than an occasional comfort upgrade.

How Does a Fixed Split-System Air Conditioner Work?

A fixed split-system air conditioner physically transfers heat from inside the property to the outdoors.

It normally consists of:

• An indoor unit
• An outdoor unit
• Refrigerant pipework
• Electrical connections
• A condensate drainage system

The indoor and outdoor units operate as part of a closed refrigerant circuit.

Inside the room, the refrigerant absorbs heat through the indoor heat exchanger. The compressor then changes the refrigerant’s pressure and temperature, allowing the captured heat to be released through the outdoor unit.

The refrigerant continues circulating through the system rather than being consumed during normal operation.

Unlike a single-hose portable air conditioner, a split system does not continuously expel conditioned room air through an open window. The compressor is also positioned outdoors, helping to reduce noise inside the home.

Many modern split systems are reversible. During colder weather, they can move heat into the property and operate as efficient air-to-air heat pumps.

This year-round capability strengthens the case for treating a fixed system as part of the home’s permanent heating and cooling infrastructure rather than a temporary appliance used during occasional heatwaves.

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Is Air Conditioning a Form of Climate Adaptation?

A Founder’s View

The UK still culturally views air conditioning as an unessential luxury – a mindset that feels increasingly out of touch with our changing climate. Across mainland Europe, where historic heatwaves are driving record adoption of cooling systems, modern, highly efficient AC is rightly seen as essential infrastructure. What is frustrating from an industry perspective is the lack of joined-up government thinking: policies push for winter heating efficiency, yet largely ignore that air-to-air heat pumps (air conditioning) offer incredibly efficient, life-saving climate control during these increasingly dangerous summers. We need to stop treating summer cooling as an unessential luxury and start treating it as vital climate adaptation.

– Matthew Powell, Founder

This shift in perspective is not without precedent. Lee Kuan Yew, the founding Prime Minister of Singapore, famously described the air conditioner as one of the most important inventions in history, noting that it “changed the nature of civilization by making development possible in the tropics.” While the UK does not have a tropical climate, we are facing a similar imperative to adapt our indoor environments so they remain safe and livable.

Climate adaptation involves changing buildings, infrastructure and behaviour to cope with conditions that are already occurring or are increasingly likely to occur.

In residential properties, summer adaptation may include:

• External window shading
• Improved ventilation
• Solar-control glazing
• Reflective roofing measures
• Reduced internal heat gains
• Better-designed extensions
• Ceiling fans
• Secure nighttime ventilation
• Mechanical cooling

Air conditioning can be part of this broader approach, especially when passive measures cannot maintain comfortable indoor temperatures.

It should not always be the first or only solution.

A home with intense solar gain may still benefit from external shading after air conditioning has been installed. Reducing the amount of heat entering the room lowers the cooling load and can reduce the electricity required to maintain the target temperature.

The best approach is not to choose between cooling and building improvements, but to use both wisely.

Why Professional Air-Conditioning Design Matters

An Engineer’s View

Choosing the correct size for your air conditioning unit is absolutely critical, as an oversized system will cycle on and off too rapidly without dehumidifying the air. We always assess the unique cooling load of your space to ensure consistent comfort and maximum energy efficiency.

– Rhys Powell, Engineer

A permanent air-conditioning system affects several parts of the property. A split-system installation can involve:

• Drilling through external walls
• Routing refrigerant pipework
• Installing condensate drainage
• Providing suitable electrical connections
• Securing an outdoor unit
• Sealing penetrations through the building envelope
• Positioning indoor units for even airflow
• Commissioning the refrigerant circuit

Poor installation can lead to water leaks, excessive noise, reduced performance, damaged finishes or unwanted air leakage around wall penetrations.

Unit placement is also important. An indoor unit should distribute conditioned air evenly without directing a continuous draught towards beds, desks or seating areas.

The outdoor unit also needs sufficient airflow, secure mounting and suitable access for future maintenance. Its position should take nearby windows, neighbours and potential noise disturbance into account.

A professional design should integrate the system with the building rather than simply attach it to the nearest available wall.

Good installation is not only about where the units are positioned. It also depends on how the refrigerant circuit is connected, tested and commissioned, which is where F-Gas certification becomes important.

Why F-Gas Certification Matters

Air-conditioning refrigerants must be handled correctly.

UK rules require technicians carrying out certain work on stationary air-conditioning equipment containing fluorinated greenhouse gases to hold the appropriate F-Gas qualifications. This includes installation, servicing, leak checking and refrigerant recovery.

F-Gas certification demonstrates that an engineer has been trained to work with these refrigerants and associated equipment.

This matters because the refrigerant circuit must be correctly connected, tested and commissioned. A leaking or incorrectly charged system may perform poorly and release refrigerant into the atmosphere.

WarmZilla’s fixed air-conditioning systems are installed by F-Gas registered engineers.

Certification should form part of a wider professional standard that also considers system sizing, electrical safety, condensate management, workmanship and the integrity of the property envelope.

What Does SEER Mean?

SEER stands for Seasonal Energy Efficiency Ratio.

It shows the seasonal cooling efficiency of an air-conditioning system under standardised test conditions. Generally, a higher SEER means the system can provide more cooling per unit of electricity consumed over the cooling season.

However, SEER is not the only factor to consider.

Real-world energy use also depends on:

• Outdoor temperatures
• The chosen thermostat setting
• Hours of operation
• Room heat gains
• System sizing
• Maintenance
• Filter condition
• Door and window use
• Solar shading
• Installation quality

Setting an air conditioner to its lowest temperature does not make the room cool faster. It simply keeps the system running until that lower setting is reached.

A moderate thermostat setting, combined with shading and sensible window use, can reduce the amount of work the system needs to do.

The same principle applies before air conditioning is installed: the less heat that enters and builds up inside the property, the easier it is to keep the home comfortable.

How Can Homeowners Reduce Overheating?

Before choosing a cooling system, homeowners should first identify how heat enters and accumulates inside the property.

Useful measures may include:

Shade Windows During Direct Sunlight

Close blinds or curtains where appropriate and consider external shading for windows that receive substantial solar exposure.

Ventilate When It Is Cooler Outside

Opening windows during the hottest part of the day can allow more warm air into the home.

Ventilation is generally more effective when the outdoor temperature has fallen below the indoor temperature.

Create Cross-Ventilation

Where the layout and security allow, opening windows on opposite sides of the property can create a path for air to move through the home.

Reduce Internal Heat

Turn off unnecessary lights, computers and other electrical equipment. Cooking during cooler parts of the day may also help. UKHSA recommends these steps to reduce internal heat.

Review Loft and Roof Spaces

Upper-floor rooms can experience strong heat gains through the roof, particularly where loft conversions have limited ventilation or large roof windows.

Consider Solar-Control Measures

Window films, specialist glazing and external shading can reduce the amount of solar energy entering problem rooms.

Identify Recurring Hot Spots

Assessing the property room by room can reveal whether the whole home needs cooling or whether the main problem is limited to one or two bedrooms, loft spaces or home offices.

These measures may reduce overheating or remove the need for mechanical cooling altogether. Even where they cannot keep the property comfortable on their own, they can reduce the amount of heat a fixed system must remove and help it operate more efficiently.

Prepare Your Home For Hotter Summers

For homes that overheat repeatedly, cooling may need to become part of the property’s long-term design rather than a temporary response to the next heatwave.

A correctly sized split-system air conditioner provides a permanent means of transferring unwanted heat outdoors. WarmZilla offers fixed-price air-conditioning packages with installation by F-Gas registered engineers.

Complete the WarmZilla air-conditioning survey to answer a few questions about your property, compare suitable systems and receive a quote based on your cooling requirements.

Frequently Asked Questions

Why Do UK Homes Stay Hot At Night?

Walls, floors, roofs and furniture can absorb heat throughout the day before releasing it later.

When outdoor temperatures remain high overnight, the property has less opportunity to release this stored heat before the following day.

Can Insulation Make A Home Overheat?

Insulation is not usually the only cause of overheating.

It can slow the entry of outdoor heat into the home, but it may also slow the escape of heat that has already built up from sunlight, occupants, appliances, and cooking. Shading and ventilation must therefore be considered alongside insulation.

Is Fixed Air Conditioning Worth Installing In A UK Home?

It may be worthwhile where a property overheats repeatedly and shading or ventilation cannot maintain a comfortable temperature.

A fixed split system can provide quieter, more consistent cooling than a portable unit, and many modern systems can also provide heating during colder weather.