Mechanical Ventilation and Indoor Air Quality in London Homes
Revised 28/11/2025
How MVHR transforms comfort, health and energy performance
Indoor air quality is often treated as an afterthought. You may notice a room feeling stuffy, or you may see condensation on a window, but the deeper story is about the air you breathe every day. In a London home, moisture and pollutants build up quietly. Over time they affect your health, your comfort and the condition of the building itself.
If you are planning a renovation or retrofit, you have a significant opportunity to put this right. This guide explains what affects indoor air quality, why ventilation matters, and how a mechanical ventilation heat recovery system (MVHR) can create a healthier, quieter and more energy-efficient home.
What is indoor air quality?
Londoners live with the reality of traffic pollution, dust, pollen and industrial emissions. We often assume that closing the front door keeps these issues outside. It does not. Because we spend close to 90 percent of our time indoors, the quality of the air inside matters more than many people realise.
Poor indoor air quality can lead to:
• breathing and lung problems
• aggravated asthma or allergies
• skin irritation
• headaches and reduced concentration
• mould-related health issues
Indoor air quality is influenced by several everyday activities. Breathing releases carbon dioxide and moisture. Cooking, bathing and drying laundry add even more humidity. Furniture, cleaning products and older building materials can release volatile organic compounds. These pollutants need to be removed and replaced with fresh air if a home is to stay healthy.
Why ventilation matters
Opening windows is the simplest form of ventilation, but it is not always possible in city homes. You may be dealing with noise, privacy issues, pollution or security concerns. When windows stay shut, moisture and pollutants remain trapped. This is when condensation, mould and stale air begin to appear.
Ventilation is essential for three reasons.
It removes moisture before it becomes condensation or mould.
It replaces stale air with oxygen-rich fresh air.
It reduces the concentration of pollutants inside the home.
A well-ventilated home is easier to heat, easier to keep clean and far more comfortable day to day.
What is MVHR?
Mechanical ventilation with heat recovery is a whole-house system that continually brings in filtered fresh air while extracting stale, moist air. The clever part is the heat exchanger. This transfers heat from the outgoing air to the incoming air, so you keep most of the warmth you have already paid to generate.
An MVHR system includes:
• an MVHR unit, usually in a loft or utility cupboard
• supply ducts delivering fresh air to living spaces and bedrooms
• extract ducts removing air from bathrooms, kitchens and utility spaces
• filters that clean both incoming and outgoing air
What to consider if you want MVHR in a London home
1. The size of the unit
A typical three or four-bedroom home needs a compact unit that fits within a cupboard, plant room or loft space. Filters should be accessible, as they need changing at least twice a year.
2. Where to place the unit
It is usually placed near an external wall or roof. Cooler locations such as a north-facing loft often work well. Units can sit in insulated or uninsulated spaces, although unheated lofts may require additional acoustic and thermal considerations.
3. Coordinating the ductwork
The ducts move like the legs of a spider through floors, walls or ceiling voids. Good coordination is essential. You want clean, well-shaped rooms without awkward boxing or bulky soffits. This is where early planning during a retrofit makes the difference between a calm, uncluttered home and a compromised one.
4. Retrofitting older buildings
Victorian and Edwardian homes often have limited voids for ductwork. Whole-house MVHR is still possible during a full refurbishment, but individual through-wall MVHR units or multi-room extract systems may be a better interim step. These improve air quality but do not recover heat as efficiently.
5. The opportunity of a full retrofit
If you are planning insulation upgrades or a whole-house refurbishment, this is the perfect moment to integrate MVHR. You avoid disruption later, and you benefit from the full comfort and energy performance of a coordinated fabric-first retrofit.
Why MVHR is good for you
Cleaner air
MVHR filters both incoming and outgoing air. Dust, pollen, pollution and many airborne particles are removed before they reach the rooms where you spend your time. Homeowners often report that their sleep improves and allergies ease. The first filter change is usually a shock because it shows how much pollution has been captured.
A warm, dry home
Constant low-volume ventilation keeps moisture at safe levels. Temperatures feel more even from room to room. Laundry dries more quickly. Bathrooms recover faster after showers. Towels stay dry without needing heated rails.
Quiet comfort
Fresh air arrives without opening windows, so you have less noise from traffic, neighbours or wildlife. Many owners describe an MVHR home as calmer and noticeably more peaceful.
Lower energy use
Because up to 90 percent of the heat is recovered through the exchanger, you lose far less warmth than with a traditional extract fan. MVHR supports highly insulated, airtight homes and forms a core part of Passivhaus design.
Why MVHR is good for your home
Better long-term condition
Moisture is one of the biggest threats to building fabric. Reducing humidity protects plaster, joinery and structure. Over time your home stays in better condition and is easier to maintain.
A future-proof feature
As energy prices rise and London’s climate shifts, homes with excellent ventilation and airtightness will hold their value. Buyers increasingly look for quiet, efficient, low-maintenance homes with good air quality.
Why MVHR is good for the environment
Supports a fabric-first approach
A well-designed retrofit begins with insulation, airtightness and moisture management. MVHR ties these elements together. It allows you to build a highly insulated, low-energy home that uses far less heating for the same level of comfort.
What to do next
If you are planning a renovation or full-house retrofit, early ventilation design is one of the most effective ways to improve comfort and health. A quiet, dry, warm home feels different the moment you walk in. Good air quality is not something you notice only when it is missing. It becomes part of the background calm of everyday living.
At Studio CMA, we integrate MVHR design into our sustainable retrofit strategy and our full architectural service.
If you have a project in mind and want to create a healthier and more energy-efficient home, reach out to discuss your project.
Frequently asked questions
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An MVHR system brings in filtered fresh air and removes stale, moist air. A heat exchanger transfers warmth from the outgoing air to the incoming air, so the home stays comfortable with less energy use.
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MVHR is ideal for London homes that suffer from noise, pollution, condensation or mould. It provides clean, continuous ventilation without opening windows, which is helpful in busy urban areas.
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Yes, but planning is important. These homes often have limited voids, so the best time to install MVHR is during a full retrofit or extension. Individual through-wall units can work as an interim solution.
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Costs vary with property size and the extent of refurbishment. A whole-house system for a three or four-bedroom London terrace is usually installed as part of a larger retrofit. The benefit is long-term comfort, better air quality and lower heating demand.
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A well-designed system is very quiet. Air is delivered at a low volume, so most homeowners only notice the improved freshness rather than any sound.
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Filters are usually replaced twice a year. This protects indoor air quality and ensures the system performs efficiently.
