Ventilation & Indoor Air Quality
Poor air quality and stuffiness signal inadequate ventilation. Measuring CO₂, humidity and airflow shows whether the home is genuinely ventilated.
Why is my house so stuffy?
A stuffy home is one where the air is not being changed often enough. Carbon dioxide from breathing builds up, moisture and smells linger, and the air feels heavy and stale — all signs that fresh air is not arriving and used air is not leaving at the rate the household needs. Stuffiness is rarely about temperature; it is about ventilation, and it is very fixable once you understand why the air is not moving.
Read the guideWhat are the signs of poor ventilation?
Poor ventilation rarely announces itself directly — instead it shows up as a cluster of everyday symptoms: misting windows, stuffy rooms, lingering smells, recurring mould and air that only feels fresh when a window is open. Recognising these signs early matters, because they point to a home that is not changing its air often enough to stay healthy and dry.
Read the guideHow do I improve indoor air quality at home?
Improving indoor air quality is not about masking smells or running an air purifier — it is about controlling the things that pollute indoor air at source and ventilating the home properly so they are removed. Moisture, carbon dioxide, fine particles and chemical pollutants each have a source and a remedy, and the most reliable way to improve the air is to measure what is actually in it and ventilate accordingly.
Read the guideDo I need MVHR or will extract fans do?
Choosing between MVHR and extract fans is one of the most common ventilation questions — and the honest answer is that it depends on how airtight your home is and what you need the ventilation to do. Extract fans remove moisture at source; MVHR supplies filtered fresh air everywhere and recovers heat. Understanding what each does, and matching it to your home, is the key to ventilating well without wasting money or heat.
Read the guideWhat humidity should my house be?
A healthy home generally sits in a moderate band of relative humidity — broadly around the middle of the scale, neither persistently damp nor uncomfortably dry. When indoor humidity stays too high, it feeds condensation, mould and dust mites; too low and the air feels dry. But the number itself matters less than what it tells you: persistently high humidity is a signal that the home is generating more moisture than its ventilation can remove.
Read the guideWhy isn't my extractor fan clearing the steam?
An extractor fan that runs but leaves the room full of steam is usually not removing anywhere near the air it should — because it is underpowered for the room, badly ducted, poorly positioned, or simply not run long enough. A fan spinning is not the same as a fan extracting. If the steam lingers, the moisture stays in the home and feeds condensation and mould, so it is worth finding why the extract is failing rather than assuming the fan is doing its job.
Read the guideDo I need to open windows if I have MVHR?
With a properly designed and commissioned MVHR (mechanical ventilation with heat recovery) system, you do not need to open windows for fresh air — that is exactly what the system provides, continuously and to every room, while recovering most of the heat from the air it extracts. Opening windows simply bypasses the heat recovery and lets that warmth escape. There are times when opening windows is still useful — for summer cooling, or to clear a one-off strong smell — but for everyday fresh air and moisture removal, MVHR is designed to do the job with the windows shut.
Read the guideWhy is my house too dry in winter?
A home often feels dry in winter for a simple, physical reason: cold outdoor air holds very little moisture, and when that air comes inside and is heated, its relative humidity falls sharply, leaving the indoor air dry. The colder it is outside, the more pronounced the effect. It is the reverse of the summer/condensation problem and usually nothing is wrong — but if the air is uncomfortably dry, the answer is gentle humidity management, not turning off ventilation, which would simply trade dryness for condensation.
Read the guideDo I need a PIV unit to stop condensation and mould?
A positive input ventilation (PIV) unit can help reduce condensation and mould in the right home, but it is not a universal cure, and fitting one before understanding the cause often disappoints. A PIV works by gently introducing filtered air, usually from the loft, into the home to slightly pressurise it and dilute and displace the humid internal air. That can lower whole-house humidity effectively where the problem is generally damp, stale air across the dwelling. But where the mould is driven by a specific cold surface, a localised moisture source, a leak or inadequate extraction at source, a PIV may make little difference. Whether you need one depends on diagnosing why the home is humid and whether the building suits positive input ventilation.
Read the guideWhy is my MVHR not working properly?
When a mechanical ventilation with heat recovery (MVHR) system does not seem to be working — the home feels stuffy or humid, there is condensation, or the unit is noisy or draughty — the cause is rarely a faulty unit. Far more often the system was never properly commissioned, is out of balance, has blocked filters or ducts, or was poorly designed and installed. An MVHR only delivers good air quality and heat recovery if it is set up to move the right amount of air to and from each room and kept maintained; without that, even a good unit underperforms. Diagnosing which of these is at fault — commissioning, balance, blockage, design or maintenance — is what gets the system actually working.
Read the guideDo I need mechanical ventilation in my home?
Whether your home needs mechanical ventilation depends on how much moisture it produces, how airtight it is, and how well it can ventilate naturally. As homes are sealed up to save energy, the accidental draughts that used to carry away moisture and stale air disappear — so a tighter home increasingly needs deliberate, mechanical ventilation to stay healthy. The right answer ranges from improved extract fans, to a positive-input ventilation (PIV) unit, to whole-house mechanical ventilation with heat recovery (MVHR), and depends on measuring the home's actual conditions rather than guessing. The aim is controlled, adequate ventilation that removes moisture and pollutants without throwing away heat.
Read the guideWhy is the air in my bedroom stale in the morning?
Waking to stale, stuffy bedroom air is almost always a sign that the room was under-ventilated overnight — carbon dioxide and moisture from your breathing built up in a closed room faster than the small amount of air change could remove them. A sleeping person exhales CO₂ and water vapour continuously, and in a modern, fairly airtight bedroom with the door and windows shut and no working trickle vent or fan, those levels climb through the night, leaving the air feeling stale and humid by morning — and often misting the windows. It is a ventilation problem with a ventilation solution, and it matters because high overnight CO₂ is linked to poorer sleep quality.
Read the guideHow do I ventilate a home without losing heat?
Ventilating a home without losing heat seems contradictory — fresh air comes in cold and warm air goes out — but it is exactly what controlled ventilation, and especially heat recovery, is designed to solve. The trick is to stop ventilating by accident, through draughts and open windows that dump heat uncontrollably, and instead ventilate deliberately at the right rate, recovering the heat from the air you expel. In a leaky home the priority is to seal the uncontrolled leakage and provide good extract; in an airtight home, mechanical ventilation with heat recovery (MVHR) supplies fresh air and reclaims most of the warmth from the stale air leaving. Either way, the answer is controlled ventilation, not no ventilation.
Read the guide