Overheating in UK Homes

The Stats That Demand Action

Overheating is no longer a rare issue—it’s a growing public health risk. The introduction of Part O of the Building Regulations was driven by clear evidence of widespread heat-related discomfort in UK homes.

Part O Key Statistics: 80% of homes overheat

80% of UK homes experienced overheating

A 2022 study by the University of East London found that 80% of UK homes experienced overheating during recent heatwaves—up from just 18% in 2011.

This isn't just discomfort - it's a design and compliance failure.


75% of Living Rooms and 57% of Bedrooms Overheated

In a study of post-2010 low-energy homes, three-quarters of living rooms and over half of bedrooms exceeded comfort thresholds (>25°C for more than 5% of occupied hours). Many of these homes included MVHR systems.


•    Overheating persisted despite high insulation and air tightness
•    MVHR systems without summer bypass or adequate airflow failed to cool
•    Rooms with poor cross-ventilation or sealed windows performed worst

75% of Living Rooms and 57% of Bedrooms Overheated

MVHR Systems Can Exacerbate Heat Without Proper Design

Surprisingly, homes fitted with MVHR sometimes showed:


Higher average indoor summer temperatures

While MVHR systems are designed to retain warmth in winter, they can unintentionally retain heat during the summer if not properly equipped with a summer bypass. Without this feature, the system continues to recover heat even when it’s not needed, causing warm air to recirculate indoors.


Reduced temperature fluctuations

MVHR systems create a sealed, airtight environment with controlled ventilation. While this improves energy efficiency, it can also mean that internal heat—whether from cooking, appliances, or solar gain—has nowhere to escape. Without natural ventilation or active cooling, the heat becomes "locked in," leading to consistently warm indoor conditions with little variation between day and night. 


Night-time overheating

Bedrooms are particularly vulnerable to overheating at night if windows are closed for noise, pollution, or security reasons. In these cases, an MVHR system must provide adequate "purge" ventilation—short bursts of high airflow that help flush out warm air and bring in cooler outside air. Without this functionality, heat lingers in bedrooms overnight, leading to uncomfortable sleeping conditions.

Part O of the Building Regulations was introduced to reduce the risk of overheating in new residential dwellings in England. With homes becoming more airtight and summers growing hotter, overheating is a growing health risk — especially in flats and urban developments.

Key aims of Part O:
•    Limit unwanted solar gain
•    Ensure effective removal of excess heat
•    Support health, safety, and comfort of occupants

Applies to: New-build homes, including flats, houses, and student housing
Doesn’t apply to: Extensions, conversions, or non-residential buildings

ResiDUCT™ provides the perfect partnership for MVHR units needed to mitigate overheating in residential dwellings

Superior Performance

Superior Performance

52%

Reduction in air leakage with ResiDUCT™ when compared with other typical ductwork used in MVHR installations. (independently tested)

Energy Efficiency

Energy Efficiency

34%

Reduction in MVHR fan speed to meet Regulations and designed rates when installed with ReisDUCT™.

Project Savings

Project Savings

40%

Reduction in costs when comparing ResiDUCT™ to other metal ducting systems needed to achieve higher airflow rates for overheating regulations.

MVHR Service - Why is it important?

Simplified vs modelling routes to compliance under Part O

Simplified Method (For Low-Risk Homes)

•    Limits glazing by orientation
•    Requires shading on large glazed areas
•    Night cooling assumed via open windows
•    Suitable for suburban homes with good cross-ventilation

Dynamic Thermal Modelling (For Complex Homes)

•    Required for flats, single-aspect units, or urban areas
•    Assesses risk using CIBSE TM59 modelling
•    Offers design flexibility — but needs expertise
Close Cookies

The Air Shop 365 Ltd Privacy Preference Center

General Description

General Description

This cookie tool will help you understand who is using cookies to collect information from your device, for what purposes they use the information, and how you can control the use of cookies for non-essential activities.

The Air Shop 365 Ltd supports the Self-Regulatory Principles for Online Behavioral Advertising of the Digital Advertising Alliance (DAA), the Digital Advertising Alliance of Canada (DAAC), and the European Interactive Digital Advertising Alliance (EDAA).

If you opt out of advertising cookies, you may still see The Air Shop 365 Ltd ads on other sites, but those ads will not be customized by us or our service providers and we will continue to customize your experience on our website via our use of cookies you have not refused.

Alternatively, privacy settings in most browsers will allow you to prevent your browser from accepting new cookies, have it notify you when you receive a new cookie, or disable cookies altogether. If your browser is set to not accept any cookies, you will not receive Interest-Based Advertising, but your use of the The Air Shop 365 Ltd service may be impaired or unavailable. In addition, if you use our cookie tool to opt-out of certain cookies, your opt-out preferences will be remembered by placing a cookie on your device. It is therefore important that your browser is configured to accept cookies for your preferences to take effect. If you delete or clear your cookies, or if you change which web browser you are using, you will need to set your cookie preferences again.

Note that from time to time we are over-inclusive in which cookies are listed in the opt-out tool. For example, we do not use Facebook, Twitter or Google cookies in all regions.

For more information on our use of cookies, please read our Cookies Policy.

Essential Cookies
Performance and Functionality Cookies
Advertising Cookies