DOMESTIC VENTILATION
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Combatting the heat: why ventilation is key
New build homes are increasingly overheating as they become more thermally efficient to improve energy efficiency and reduce carbon emissions. Steve Pearce, product manager at Vent-Axia, discusses overheating challenges and how the newest ventilation solutions can help reduce overheating
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n the UK, our homes have not traditionally struggled with overheating. However, today’s new build homes are far more airtight with high
levels of insulation, large glazed areas, and little solar shading, which all increase overheating risks. In addition, the limited number of openable windows, due to noise, air pollution, or security considerations, have also increased the risk. Climate change and increasing summer
temperatures also add to the overheating problem in new build homes. In addition, urbanisation has contributed to raised temperatures, especially in city centres, like London, where the Urban Heat Island eff ect can elevate nighttime temperatures by 10ºC compared to its surrounding rural areas. As a result, some new homes are experiencing indoor temperatures above comfort levels, and in some cases the temperatures are posing health risks.
Part O
The UK Government recognised the seriousness of the overheating problem, introducing Approved Document O of the Building Regulations in 2021. Part O addresses overheating in new dwellings, care homes, and student accommodation. Its core objective is to protect occupant health and wellbeing rather than aimed at thermal comfort. It has two overarching requirements: limiting unwanted solar gains and ensuring excess heat can be removed from the home. When it comes to limiting solar gains and
removing excess heat, Part O prioritises passive measures fi rst. Part O off ers two calculation methods to meet requirements: the Simplifi ed Method which is suitable for sites that are not aff ected by noise or air pollution; and the Dynamic Thermal Modelling (CIBSE TM59), where simplifi ed compliance is not possible. Ventilation is an important part of the solution
for overheating. Part O lists acceptable methods in order of preference, starting with opening windows, followed by ventilation louvres, mechanical ventilation, and lastly mechanical cooling. There are a number of diff erent types of ventilation that can be used to combat overheating.
Extract ventilation
When it is not possible to use windows for ventilation, modern extract systems, such as specifi cally designed unitary fans with built-in temperature sensors and complete inline solutions,
30 June 2025
can help remove excess heat. For example, Vent- Axia’s NBR CoolBox Kits off er on-demand heat extraction. Designed as a complete all-in-one boxed solution to help satisfy overheating requirements in dwellings, these systems are compact, low-noise, and suitable for installation in all habitable rooms. They off er on-demand operation or automatic switching, ensuring effi cient performance aligned with occupant needs.
MVHR
Now a core part of low-carbon building design, the latest Mechanical Ventilation with Heat Recovery (MVHR) units, such as Vent-Axia’s Lo-Carbon Sentinel Econiq, deliver coolth or heat recovery effi ciencies of up to 93%. Off ering complete controllability, the Lo-Carbon Sentinel Econiq provides year-round comfort in new build homes. Crucially for overheating mitigation, the Lo-Carbon Sentinel Econiq comes with intelligent automatic 100% summer bypass
Left: Steve Pearce, product manager at Vent-Axia
capabilities, off ering free cooling, allowing night- time air to fl ow through the home when conditions permit. These systems also provide excellent indoor air quality through high-grade fi ltration, vital in urban developments with high external pollution.
MVHR DX
However, when MVHR alone is insuffi cient to tackle overheating throughout the year, specifi ers can consider all the benefi ts of MVHR systems with integrated DX cooling modules, such as Vent-Axia’s Lo-Carbon Sentinel Econiq Cool-Flow. Featuring intelligent controls that automatically switch between heat recovery, summer bypass, and active cooling via the DX cooling module, the units continuously measure internal and external temperatures to maintain comfort thresholds effi ciently. This helps ensure homes remain cool, comfortable, and energy-effi cient. The intelligent DX cooling module can activate on- demand or automatically to prevent overheating.
MVHR + hot water heat pumps
One of the latest innovations available is a new mechanical cooling option for specifi ers, which combines an MVHR unit with a hot water air source heat pump. This type of system combines two technologies, off ering 2-in-1 – renewable hot water and a free cooling solution. For example, the Lo- Carbon Sentinel Econiq-Cool (KERS), Vent-Axia’s latest fl agship MVHR system, features all-new controls allowing communication with the KERS Coolboost Heat Pump. This system monitors comfort temperatures defi ned by the user, and when cooler outdoor air is not suffi cient to cool the space via the 100% summer bypass, the system automatically sends a signal to the heat pump to request cooling. This will then combine the air fl ow from the MVHR and the cool exhaust air of the heat pump via built-in dampers. This type of system off ers the highest level of comfort and functionality all year round, while being extremely energy effi cient, heating hot water and cooling habitable spaces at the same time. With overheating becoming an increasing problem in new build homes it is important to consider the low carbon ventilation solutions that are available to tackle it. Overheating is a serious health issue, but it is also a comfort issue, which is why ventilation is key to solving the overheating challenge and helps futureproof homes against the climate changes ahead.
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