Renovating homes can improve energy efficiency, comfort and carbon emissions, but it can also reduce natural air renewal by making buildings more airtight. Without effective ventilation, indoor air pollutants, humidity and mould risks can increase. A successful renovation should therefore assess the existing ventilation strategy, ensure continuous airflow, and select systems that combine indoor air quality (IAQ), energy efficiency and verified performance. Certified residential ventilation systems help specifiers, installers and homeowners rely on accurate product data when choosing solutions for healthier, lower-carbon homes.
When it comes to renovation projects, energy performance and ventilation must go hand in hand. Whenever insulation, airtightness or glazing is improved, the ventilation strategy should be checked, adapted or upgraded to protect indoor air quality and building performance.
In existing homes, poor or absent ventilation can affect both occupants and the building itself. Pollutants, excess humidity and stale air can accumulate indoors, contributing to discomfort, respiratory irritation, allergies, condensation and mould growth. Opening windows may provide occasional air renewal, but it is not a controlled, energy-efficient or reliable ventilation strategy, particularly where cold, hot, noisy or polluted outdoor conditions exist.
Renovation projects often focus on reducing heat losses by improving insulation and airtightness. Replacing old windows with high-performance glazing is a common example. However, when a building becomes more airtight, air that previously entered through gaps, leaks or frequent window opening may no longer be renewed naturally. If the home already has a regulated ventilation system, replacement windows must maintain the correct air inlets for that system. If the home has no mechanical ventilation, the renovation can unintentionally reduce air change rates and compromise indoor air quality.
Decarbonising existing housing stock is not only about adding insulation, replacing heating systems or installing renewable energy. It is about improving whole-building performance. Ventilation systems play a vital role because they help renovated homes remain healthy, efficient and comfortable as airtightness improves. Solutions such as heat recovery ventilation and demand-controlled airflow can reduce unnecessary heat losses while ensuring the right level of fresh air. In this way, well-designed ventilation supports lower energy demand, reduced emissions and better indoor environmental quality.
A ventilation audit should be one of the first steps in any renovation project. It can identify whether the existing system is present, correctly sized, properly connected and capable of providing continuous ventilation in all relevant rooms. Where ventilation is neglected, the renovation can make indoor air quality worse, even when the building fabric becomes more energy efficient.
Small changes can make a big difference. New flooring can reduce the gap under internal doors and disrupt airflow between rooms. Existing ducts may be accidentally disconnected, damaged, dirty, poorly sealed or responsible for excessive pressure drops. Extract airflow may then become insufficient, leaving kitchens, bathrooms and WCs under-ventilated. An audit helps identify these weaknesses before specifications are finalised, ensuring that the chosen ventilation approach supports both compliance and occupant wellbeing.
Where a home already has mechanical ventilation, renovation may provide the opportunity to optimise or replace the existing system. Hygro-adjustable single-flow systems, for example, adapt airflow according to humidity and occupancy-related needs, helping reduce unnecessary ventilation losses. In single-flow systems, fresh air is normally introduced into living rooms and bedrooms, while stale air is extracted from service rooms such as kitchens, bathrooms and WCs.
Double-flow systems, also known as balanced ventilation systems, or mechanical ventilation with heat recovery (MVHR), extract stale air and supply filtered fresh air mechanically. Many include a heat exchanger that transfers useful heat from outgoing air to incoming air, reducing heating demand while maintaining controlled ventilation. In well-insulated and airtight renovated homes, this can be a strong option for combining indoor air quality, energy efficiency and comfort.
Not every renovation project can easily accommodate a centralised ducted system. In some existing single-family homes, installing an extraction unit and duct network may be difficult, costly or disruptive. Decentralised ventilation can provide an alternative by ventilating specific rooms locally, while supporting general air movement through correctly designed transfer paths. Service rooms may be equipped with extract units, while main rooms receive fresh air through appropriate inlets. As with any system, performance depends on correct design, installation, commissioning and maintenance.
Ventilation products are selected on the basis of performance data: airflow, pressure drops, leakage, sound levels, electrical consumption, heat recovery efficiency and seasonal energy performance. If this data is inaccurate, products can be incorrectly sized or specified, leading to higher energy use, poor acoustic comfort, insufficient air renewal or non-compliance with regulations. Independently verified data gives specifiers, installers and homeowners greater confidence that the selected system will perform as expected in the intended application.
Eurovent Certification provides independently verified data for a wide range of residential system types:
Eurovent Certified Performance for Residential Air Handling Units provides independently verified product performance data and proves regulatory compliance for MVHR systems for residential use.
Eurovent Certified Performance for Indoor Air Quality and Energy Efficiency provides independently verified product performance and energy efficiency data for full ventilation systems for use in residential dwellings in individual housing.
The NF205 certification programme for residential ventilation provides independently verified product performance data for self-regulating air inlets, extraction vents, single flow & double flow units.
The Residential Ventilation QB37 certification programme provides independently verified product performance data for devices that are part of a single flow Controlled Mechanical Ventilation (CMV) system providing humidity control.
Certification supports transparent comparison between products and helps decision makers select systems using data that has been checked through an impartial process. For renovation projects, this matters because the wrong product choice can affect indoor air quality, running costs, acoustic comfort and the credibility of wider decarbonisation measures.
Renovation often makes a home more airtight. Without a suitable ventilation strategy, pollutants, humidity and stale air can build up indoors, increasing the risk of discomfort, condensation and mould.
The best solution depends on the building layout, airtightness, available space, indoor air quality needs, budget and renovation scope. Options can include optimised single-flow ventilation, balanced ventilation with heat recovery or decentralised systems. An audit should be carried out before selecting a solution.
Eurovent certified residential ventilation systems provide independently verified performance data, helping specifiers, installers and homeowners compare products with confidence. Verified data reduces the risk of selecting equipment based on unproven claims and supports healthier, more energy-efficient homes.
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View our residential ventilation programmes:
Residential Air Handling Units
Indoor Air Quality and Energy Efficiency
Residential Ventilation - NF205
Residential ventilation - QB37
