Global temperatures are rising

Due to climate change there is a significant increase in the risk of buildings overheating worldwide. The building industry face the complex challenge of creating sustainable buildings that balance health, comfort, and energy efficiency. This involves adapting to improved building fabrics, adhering to strict regulations, and meeting the diverse needs of occupants.




CIBSE's fixed temperature test defines overheating as internal temperatures exceeding 26°C for more than 3% of the time. This not only compromises comfort but also raises health risks, with temperatures over 35°C increasing the chance of heat stress and even death.

Where does the heat come from?

Although climate change is essentially the main driver behind the temperature increase, one key reason for overheating in buildings is the improved building fabric standards, which are designed keep the building warm in winter, but trap heat inside during warmer periods.

It is a complex issue that is affected by a wide range of issues, such as increased amounts of glazing on modern buildings which allow more solar gains, or lightweight constructions which are prone to large fluctuations in temperature.

The challenges of modern building design are intensified by the higher temperatures from climate change. Many buildings today are designed without adequate passive cooling solutions, often due to environmental and security concerns.

Regulations that are driving change

To address this pressing issue, regulatory bodies have implemented new standards to ensure residential buildings maintain comfortable temperatures. Approved Document O in England and its counterparts in Wales and Scotland mandate compliance with thermal comfort regulations.

Approved Document O England

Approved Document O (2021 edition – England) was released in December 2021 and came into force for all Building Regulations building notices, full plans applications and initial notices for residential buildings submitted in England from 15 June 2022.

Approved Document O Wales

Approved Document O (2022 edition – Wales) was released in May 2022 and came into force for all Building Regulations building notices, full plans applications and initial notices for residential buildings submitted in Wales from 23 November 2022.

Scottish Building Standard 3.28

Standard 3.28 of the Scottish Building Standards Domestic Technical Handbook (December 2022 edition) was released in June 2022 and came into force for all residential Building Warrant applications submitted in Scotland from 01 February 2023.

Designing out the heat

Excessive heat in homes is not solely a result of environmental factors but also of design, making thermal modeling crucial. In addition to core design features, implementing certain solutions within the dwelling can create a win-win situation. For instance, low-energy lighting not only reduces energy usage but also helps in lowering internal heat gains.

Key Design Considerations for Overheating

  • Minimise internal heat generation through energy-efficient design.
  • Reduce heat entering the building by considering orientation, shading, fenestration, insulation, and green roofs and walls.
  • Manage heat using exposed internal thermal mass and high ceilings.
  • Incorporate natural ventilation, including openable windows and cross ventilation.
  • Integrate balanced whole-house mechanical ventilation systems, such as heat recovery with true summer bypass.
  • Utilise active, low-carbon cooling to support energy-efficient design, avoiding traditional air conditioning.
  • Ensure installation quality and design with certified, and trained installers to combat overheating.
CIBSE Accredited CPD
Our CIBSE accredited CPD offers invaluable insights into mitigating overheating. From understanding the underlying causes and new building regulations to exploring ventilation solutions, our course equips professionals with the knowledge needed to navigate these challenges effectively.

Understanding good indoor climate

A good indoor climate is a balance between health, energy efficiency, and comfort:

  • Healthy Indoor Climate: Low CO2 levels, rapid reduction of (virus) particles, prevention of dust mites and molds, reduction of fine dust and pollen.
  • Energy-Efficient Indoor Climate: Optimal (re)use of energy to reduce electricity and fossil fuel usage needed for a healthy and comfortable home.
  • Comfortable Indoor Climate: Proper temperature, rapid odor removal, appropriate humidity levels, and prevention of draughts.

Using ventilation to mitigate overheating in homes

Combining ventilation with active cooling can offer a low carbon solution to overheating issues in residential properties and can be designed in conjunction with dynamic thermal modelling.

In most instances, a mechanical ventilation system such as MEV (Central Extract System) or more likely MVHR (Heat Recovery) forms the base of the strategy for overheating. This can then be adapted accordingly to ensure compliance with best practice guidance (CIBSE TM59).


Zehnder's approach to better ventilation and cooling:

Zehnder offers various options, ranging from standalone solutions to integrated strategies, aimed at mitigating overheating whilst also balancing health, energy efficiency, and providing a comfortable indoor environment.

Our solution

LPID100 Low Profile Induct Fan

  • Designed to fit within a ceiling void, cupboard or loft space
  • 100% variable speed control via optional SDC1 controller
  • High speed only using switching by others without the need for SDC1 controller
  • Can be installed in any orientation, horizontal, vertical, on floor, wall or ceiling.
  • 4 air changes an hour for rooms up to 15m2 per fan, large rooms can use multiple fans wired in parallel

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Acoustically treated inline extractor fans located in habitable rooms provide additional ventilation up to 4 ACH in lieu of openable windows.

Quiet in operation and ideal for running at night! Can be used in conjunction with MEV and MVHR mechanical systems.

Our solution

Zehnder ComfoAir Q

  • Range of airflow performances with excellent pressure handling to reduce installed noise levels
  • Constant volume motors to ensure the delivery of guaranteed installed performance
  • Zero leakage, low pressure ducting solution for reduced noise levels and continued airflow performance

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Increased extract and supply rates (typically to around 2.5ACH) to provide purge requirements without the need for additional solutions.

Radial ducting ensures a balanced system and reduces noise and leakage to maintain lower running speeds

Our solution

True summer by-pass and passive cooling

  • Filtered fresh supply air in bypass mode to prevent dust, debris and pollutants entering the house
  • Summer by-pass works to deliver comfort – open, close, or partially opened or closed depending on internal vs. external conditions and comfort factor
  • Passive cooling via automatic increase in flow rate during favourable external conditions to rapidly bring in cooler external air
  • In favourable conditions where internal air is cooler than external air, the unit will disable the summer by-pass and instead look to offer cold recovery of up to 87%. The ComfoAir Q350 is the first unit to be certified by the PHI for its cold recovery efficiency

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Modulating bypass within MVHR system constantly aims to improve the internal comfort temperature/humidity by allowing full/partial/no heat recovery depending on conditions.

Constant volume motors ensure ventilation rates are met and help overcome increased pressure drops.

Passive cooling can be activated based on external conditions that can help maximise comfort in warmer months by automatically boosting supply air rates

Our solution

Zehnder ComfoTube Therm

  • Ideal solution for continuously insulated air distribution.
  • Optimal thermal insulation properties; tempered air is conducted into the living space with very low temperature loss
  • The sound-optimised inner skin ensures low air resistance and extremely quiet air flow even with larger air volumes
  • Corrosion-resistant and heat-resistant materials ensure longevity of solution

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Innovative Zehnder ComfoTube Therm ducting solutions ensure continuously insulated air distribution, so the living space is cooled and heated in an energy efficient manner.

Durable, whilst maintaining its flexible properties.

Our solution

Zehnder ComfoFond

  • Ground closed loop system that works in conjunction with MVHR Unit
  • Provides pre-heating during the winter and air temperation during the summer
  • Hygienic closed loop system to prevent water, dust ingress and avoid the need for maintenance of a collector of open air to air systems
  • Maintain a balanced ventilation rate down to -22°C external conditions

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Working in conjunction with the MVHR system, sealed ground loops and a water to air heat exchanger provide pre-heating in the winter and pre-cooling in the summer on the supply/intake air.

Our solution

Zehnder ComfoClime & Enthalpy

  • 1.5kW cooling capacity integrated with MVHR Unit (ComfoAir Q450 and ComfoAir Q600) and ducting network
  • Easy and space-saving installation
  • Filtered fresh supply air, not recycled stale air
  • Controlled via the ComfoAir Q450 and ComfoAir Q600s including ComfoSense C, KNX or ComfoControl app for IOS or Android

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Working in conjunction with the MVHR system, this provides 1.5KW active air temperation and dehumidification via refrigerant cycle.  Enthalpy MVHR cell passively reduces humidity of incoming fresh air under favourable internal/external conditions.

Our solution

Zehnder ComfoPost

  • Cooling and dehumidification of filtered supply air via MVHR, during peak conditions (water at 7°C)
  • Complete control and setting of temperature and humidity to improve the indoor climate
  • Good thermal and acoustic solution, no draughts or nuisance noise

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Works in conjunction with a centralised chiller system or reversible heat pump to provide 1.88-5.64KW of cooling capacity via the supply air of a constant volume MVHR system with Enthalpy cell.

Our innovative ventilation solutions

Discover more about how Zehnder’s advanced ventilation systems help regulate temperatures across various spaces, ensuring comfort and energy efficiency throughout the warmer seasons.

Looking for support on your next project?

Don't wait for overheating to become a problem, act now to beat the heat and mitigate overheating in buildings. Whether you're a developer, consultant, social housing provider, or homeowner, we're here to help. Ensure regulatory compliance, optimise designs, enhance livability, and create comfortable spaces with our expert solutions. Partner with us for a safer, more comfortable future.

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