Why ventilation matters more than you think
Ventilation quietly determines whether a home is healthy or damp, comfortable or stuffy, efficient or wasteful. Its job is to remove the moisture and pollutants that build up indoors and replace them with fresh air. Get it wrong in either direction and you have problems: too little ventilation traps moisture, causing condensation, mould and poor air quality; too much, or the wrong kind, throws heat away and leaves the home cold and expensive. The goal is controlled, deliberate ventilation — 'build tight, ventilate right'.
Most homes have never had their ventilation properly assessed. Extract fans, trickle vents and background ventilation are installed piecemeal, and rarely evaluated as a whole. A home ventilation assessment looks at the complete picture and designs a strategy that fits your home.
Extract, background and whole-house ventilation
There are several ways to ventilate a home, and the right mix depends on your property and how airtight it is. Extract ventilation removes moisture at source in kitchens and bathrooms. Background ventilation — trickle vents and similar — provides a continuous trickle of fresh air. In airtight homes, whole-house systems such as MVHR (mechanical ventilation with heat recovery) supply fresh, filtered air to living spaces and extract stale air from wet rooms, recovering most of the heat in the process. We assess which approach your home needs.
Airtightness and ventilation go together
The more airtight a home, the more important deliberate ventilation becomes. As draughts are sealed to save energy, the accidental ventilation they provided disappears, and moisture and pollutants can build up. This is why so many homes develop condensation and mould after new windows or insulation. A ventilation assessment, ideally alongside airtightness testing, ensures the two are balanced — so an efficient home is also a healthy one.
How Retrofit IQ assesses your ventilation
We review ventilation provision room by room — extract fans, trickle vents, background and any whole-house system — and measure humidity, temperature and dew point to see how well moisture is being controlled. Thermal imaging finds the cold surfaces where inadequate ventilation turns into condensation. Where relevant, blower door testing measures airtightness so ventilation can be balanced against it. You receive a clear assessment and a recommended ventilation strategy.
Part of a full Building Performance Investigation
Ventilation cannot be designed in isolation from airtightness, insulation and moisture. A home ventilation assessment is most valuable as part of a full Building Performance Investigation, which balances fresh air, warmth and efficiency in one prioritised plan.
Ventilation and energy efficiency together
Ventilation and energy efficiency can seem to pull in opposite directions — you need fresh air, but you do not want to throw away heat. The resolution is controlled ventilation, and in particular heat recovery. A mechanical ventilation with heat recovery system extracts stale, moist air and uses its warmth to pre-heat the incoming fresh air, so you gain healthy air while keeping most of the heat. This is why, in an airtight home, good ventilation and low energy bills are not in conflict but go hand in hand. Our assessment finds the balance that keeps your home both fresh and efficient.
Maintenance, filters and keeping it working
Ventilation systems only deliver if they are maintained. Extract fans lose performance if grilles clog with dust; MVHR systems need their filters cleaned or replaced periodically and their ductwork kept clear. A neglected system quietly under-performs, letting moisture and pollutants build up again. Part of a good assessment is not only recommending the right system but explaining the simple, occasional maintenance that keeps it effective — so the healthy indoor climate you invest in continues for the long term rather than fading within a year or two.
Ventilation in flats and smaller homes
Flats and smaller homes present particular ventilation challenges: fewer external walls, limited options for cross-ventilation, sometimes restricted window opening, and single-aspect layouts where fresh air struggles to reach every room. These homes can suffer condensation and stale air even when they seem modern and efficient. Tailored ventilation — often continuous mechanical extract or a compact heat-recovery system — is frequently the answer. Our assessment is well suited to flats, recognising the constraints and recommending a strategy that works within them.
How we recommend the right level
There is no single correct ventilation system for every home, which is why we assess before advising. We weigh your home's airtightness, layout, occupancy and moisture loads, and the symptoms you are experiencing, to recommend a proportionate solution — from improving and correctly using existing extract, through continuous mechanical extract, to full heat-recovery ventilation where the home can make good use of it. The aim is always the right level for your home: enough to keep it healthy and dry, without wasting heat or over-engineering the solution.
What you receive
The main ventilation strategies explained
There is more than one way to ventilate a home, and understanding the options helps you see why an assessment matters. Natural ventilation relies on windows, trickle vents and passive airflow — simple, but inconsistent and wasteful of heat in winter. Intermittent extract uses fans in kitchens and bathrooms to remove moisture at source. Continuous mechanical extract runs at a low rate all the time, with boost when needed. And mechanical ventilation with heat recovery (MVHR) supplies fresh filtered air and extracts stale air throughout the home while recovering most of the heat. The right strategy depends on how airtight your home is and how it is used, which the assessment determines.
Signs your ventilation is failing
Homes rarely announce a ventilation problem directly; instead they show symptoms. Condensation on windows and walls, black mould in corners and bathrooms, a persistent musty smell, air that feels stuffy and stale, and steam that lingers long after a shower are all signs that moist, stale air is not being removed effectively. If these appeared or worsened after new windows or draught-proofing, the link to ventilation is even clearer — the home became more airtight, but the ventilation did not keep pace. An assessment confirms whether, and where, your ventilation is falling short.
MVHR: when it makes sense
Mechanical ventilation with heat recovery is a powerful solution, but it is not right for every home. It performs best in reasonably airtight properties, where it can supply a steady flow of fresh, filtered air and recover a large share of the heat that would otherwise be lost with the extracted air. In a leaky home, much of its benefit escapes through the gaps, so airtightness usually needs addressing first. This is why we assess ventilation and airtightness together, and recommend MVHR only where the building can make good use of it — otherwise a simpler extract strategy may serve you better.
Getting installation and commissioning right
Even the best ventilation system underperforms if it is poorly installed or never properly commissioned. Extract fans sited in the wrong place, ducting that is too long or crushed, and systems left on their lowest setting all fail to remove the moisture they should. MVHR in particular must be correctly ducted, balanced and commissioned to deliver its promised performance, and its filters maintained thereafter. Our assessment considers not just what to install but how it must be set up to work — so you get the healthy, efficient result the equipment is capable of.
- A room-by-room assessment of your ventilation
- Measured humidity, temperature and dew-point findings
- Thermal images of surfaces at condensation risk
- An airtightness result where blower door testing is carried out
- A recommended, prioritised ventilation strategy
A real-world investigation example
After fitting new windows and insulation, a homeowner was baffled to find condensation and mould appearing in a house that had never had them before. A ventilation assessment made the cause plain: the improvements had made the home considerably more airtight, but the ventilation had not changed — trickle vents were closed, the bathroom fan was feeble and there was no whole-house strategy. The moisture that once escaped through draughts now had nowhere to go. A balanced plan — effective extract in the wet rooms, reinstated background ventilation and, given the airtightness achieved, consideration of heat-recovery ventilation — restored a dry, healthy home without sacrificing the energy savings.
Common homeowner mistakes
The defining mistake is treating airtightness and ventilation as separate jobs, improving one and neglecting the other, which is why so many upgraded homes develop condensation. Another is assuming more ventilation always means opening windows, wasting heat and doing it inconsistently. Homeowners often specify or reject MVHR without first establishing how airtight the home actually is, so the system is either wasted on a leaky house or missing from a tight one. And installing a system without proper commissioning and maintenance leaves it quietly under-performing.