Specialist installers of positive input ventilation (PIV) systems — also called positive pressure ventilation — for London homes, flats, and rented properties. If you’re dealing with persistent condensation, black mould that keeps coming back, or stale musty air in your home, a PIV system is likely the most cost-effective long-term solution available.
📞 020 4542 6114 | Book a free ventilation survey →
✅ Loft and wall-mounted units · ✅ Suitable for houses and flats · ✅ 4.9★ rated · ✅ London-wide installation
What Is Positive Input Ventilation (PIV)?
Positive input ventilation (PIV) — also called positive pressure ventilation (PPV) — is a whole-home or office ventilation system that continuously supplies filtered fresh air into your property to reduce condensation, eliminate mould, and improve indoor air quality.
A PIV unit draws fresh air in from outside (usually through the loft or via a wall-mounted unit), filters it, then gently introduces it into the living spaces at low positive pressure. This slightly pressurised fresh air gradually displaces the damp, stale air inside the home — pushing it out through natural gaps in windows, doors, and the building fabric.
The result is a continuous, gentle air change that keeps indoor humidity at a healthy level, prevents condensation from forming on cold surfaces, and removes the conditions that allow mould to grow.
PIV systems are increasingly the preferred solution for condensation-related damp and mould in London properties because they treat the root cause — excess indoor moisture — rather than just the symptoms.
Not sure if you need a PIV system or a different treatment? Condensation, rising damp, and penetrating damp all look similar but require completely different solutions. Book a damp and ventilation survey → and we’ll identify exactly what’s causing the problem in your property.
How Does a PIV System Work? Step by Step
Understanding the process makes it easier to see why PIV is so effective where other solutions — dehumidifiers, mould sprays, or simply opening windows — fail to deliver lasting results.
- Fresh air intake — The unit draws external air in continuously, typically from the loft space in houses, or directly from outside through a duct in flats.
- Filtration — Incoming air passes through a filter that removes pollen, dust particles, and airborne pollutants before the air enters your home. This is why PIV systems benefit allergy and asthma sufferers as well as resolving damp.
- Gentle diffusion — Filtered air is introduced at ceiling height or from a ceiling diffuser, spreading evenly across the room at low velocity — you don’t feel a draught.
- Positive pressure is created — The continuous supply of fresh air creates a slightly higher air pressure inside the home than outside. This gentle positive pressure is what makes the system work.
- Stale, humid air is displaced — The pressurised fresh air gradually pushes damp, moisture-laden air out through natural ventilation gaps — around window frames, letterboxes, door gaps, and trickle vents — without any mechanical extraction.
- Humidity stabilises — Because the incoming external air is typically drier than the moisture-laden air inside a condensation-affected home, indoor humidity levels fall and stabilise within a comfortable range. Condensation stops forming. Mould loses the conditions it needs to grow.
Signs You Need a PIV System
If you recognise any of these in your home, a positive input ventilation system is likely what you need:
Condensation on windows every morning — Water running down the inside of glass in bedrooms and living rooms is the clearest sign that indoor humidity is too high. This is a ventilation problem, not a structural one.
Black mould that keeps coming back — If you clean mould from walls, window frames, or sealants and it reappears within weeks, the underlying moisture hasn’t been addressed. A PIV system removes the excess humidity that feeds mould growth. Read our black mould removal guide →
Musty or stale-smelling rooms — A damp, musty smell — particularly in bedrooms, hallways, or rooms that are used infrequently — is caused by mould spores and stale humid air. PIV replaces this with fresh, filtered air continuously.
Mould in wardrobes or behind furniture — Condensation mould frequently grows on the cold walls behind wardrobes and behind sofas on external walls. This is a cold-bridging and ventilation issue that PIV directly addresses.
Mould in a flat with no obvious structural damp — In London flats, particularly those on higher floors or in modern buildings with good insulation, condensation is almost always the cause of mould. PIV is highly effective in these properties.
A property that feels stuffy or airless — Homes that are tightly draught-proofed and well-insulated can suffer from poor air exchange. PIV solves this without sacrificing warmth.
PIV Systems for London Houses
For houses with a loft space, a loft-mounted PIV unit is the standard solution. The unit sits discreetly in the loft, draws fresh air from the loft environment, filters it, and distributes it down into the hallway or landing through a ceiling diffuser. From there, air circulates naturally through the home.
Loft PIV systems work particularly well in:
London’s Victorian and Edwardian terraces, which have solid brick construction that gets cold in winter and creates significant condensation on internal wall surfaces. Semi-detached and detached properties where condensation is concentrated in specific rooms. Homes where rooms have been added in extensions with limited natural ventilation.
Many loft PIV units include an optional heating element. This warms the incoming air slightly during colder months so that it doesn’t reduce the ambient temperature — a practical consideration in London’s winter climate.
PIV Systems for London Flats
Flats present a specific challenge: most don’t have loft access, and many are in converted Victorian houses or purpose-built blocks where standard loft PIV installation isn’t possible. Wall-mounted PIV units — also called flat PIV units or PPV units for flats — solve this.
A wall-mounted PIV unit is fixed to an internal wall (typically in a hallway or landing), ducted through to an external wall, and operates in exactly the same way as a loft unit — supplying filtered fresh air at positive pressure to displace humid indoor air.
Wall-mounted PIV for flats is particularly effective in:
Ground floor and basement flats where condensation is compounded by cold floors and walls. Top floor flats in converted houses where loft access belongs to the building rather than the flat. Modern purpose-built apartments with mechanical ventilation that has deteriorated or is insufficient. Flats in HMOs (houses in multiple occupation) and rented properties where tenants have limited control over ventilation.
Landlords and letting agents: A PIV system is one of the most cost-effective ways to comply with your obligations under the Homes (Fitness for Human Habitation) Act 2018 regarding condensation and mould. We install PIV units in tenanted properties with minimal disruption. Read our landlord services →
PIV Installation: What to Expect
We handle the entire process from initial assessment to signed-off installation.
Survey — We assess your property to confirm that PIV is the right solution, establish which type of unit (loft or wall-mounted) is appropriate, and identify the best location for the diffuser and air intake. For most London properties, this takes under an hour.
Installation — Loft PIV installation typically takes half a day. Wall-mounted flat installations take two to four hours. Our engineers work cleanly and leave the property tidy. All electrical work is carried out to Part P standards.
Commissioning — The unit is set to the correct flow rate for your property size and confirmed operational before we leave.
What you’ll notice — Most homeowners see a reduction in window condensation within days. Mould patches stop growing and the musty smell reduces over one to three weeks as the air quality improves. Within four to eight weeks the effect is typically marked — surfaces that were previously wet every morning stay dry.
How Much Does PIV Installation Cost in London?
PIV installation costs in London depend on the property type, the unit specification, and whether additional ductwork is required.
| Installation type | Typical London cost |
|---|---|
| Loft-mounted PIV unit – heated (house) | £870 – £1020 installed |
| Wall-mounted PIV unit (flat) | £950 – £1070 installed |
| Running costs (annual electricity) | Approximately £50 – £70/year |
These are indicative ranges. We provide a fixed, itemised quote after the initial survey with no hidden charges. Compared to the cost of repeated mould remediation, replastering, and redecorating, most PIV installations pay for themselves within one to two years.
👉 Read the full London ventilation and damp treatment cost guide →
PIV vs Dehumidifier: Which Is Better for Condensation?
This is one of the most common questions homeowners ask, and it’s worth addressing directly.
A dehumidifier extracts moisture from indoor air but doesn’t replace that air with fresh air from outside. It recirculates the same indoor air repeatedly. In a poorly ventilated home, this can reduce peak humidity but doesn’t create the sustained air exchange that prevents condensation from forming on cold surfaces overnight. Dehumidifiers also require emptying, consume more electricity than PIV units, and make noise.
A PIV system works differently — it continuously replenishes indoor air with outdoor air rather than simply drying the indoor air it already has. This means it addresses the stale air quality problem as well as the humidity problem, and it does so continuously and automatically.
For most London homes with condensation-related damp and mould, a PIV system delivers better long-term results than a dehumidifier. For properties with structural damp — rising damp or penetrating damp — the underlying damp must be treated first. PIV is not a substitute for structural damp proofing.
👉 Not sure which type of damp you have? Read our guide →
PIV Installation Across London
We install positive input ventilation systems across all London boroughs, with particular experience in the flat-heavy residential areas of North and West London.
Barnet · Finchley · Hendon · Golders Green · Hackney · Haringey · Wood Green · Tottenham · Enfield · Ealing · Chiswick · Acton · Greenford · Kensington · Camden · Hampstead · Brent · Kilburn · Hertfordshire
Book a Free PIV Assessment in London
If condensation or mould is a recurring problem in your home or flat, we can assess whether a PIV system is the right solution — or whether there is a structural cause that needs treating first. Most London condensation problems are resolved within a single installation visit.
📞 Call: 020 4542 6114 📧 Email: info@dampandmouldsolutions.co.uk
Same-week appointments available across London. No obligation to proceed after the survey.
FAQ
What is a PIV system and what does it do?
A PIV (Positive Input Ventilation) system — also known as a positive pressure ventilation or PPV unit — is a whole-home ventilation system that continuously supplies filtered fresh air into your property. It works by creating a gentle positive pressure that pushes damp, stale air out through natural gaps in the building, while introducing cleaner, drier air from outside. The result is lower indoor humidity, less condensation, and the elimination of the conditions that allow mould to grow.
Does a PIV system actually stop mould and condensation?
Yes — for condensation-related mould, a properly installed PIV system is one of the most effective long-term solutions available. Condensation occurs when warm, moisture-laden air contacts cold surfaces. By continuously reducing indoor humidity through fresh air introduction, PIV prevents this from happening. Most homeowners notice significantly less window condensation within days of installation, and mould stops growing within two to four weeks. For mould caused by structural issues — rising damp or penetrating damp — the underlying damp must be treated separately.
What is the difference between PIV and PPV (positive pressure ventilation)?
In a domestic context, PIV (Positive Input Ventilation) and PPV (Positive Pressure Ventilation) refer to the same type of system — one that introduces filtered air at positive pressure to ventilate a home and reduce condensation. PIV is the term most commonly used by manufacturers and installers for residential systems. PPV is sometimes used as a broader term for positive pressure ventilation, which includes industrial and commercial applications as well. Both describe the same working principle when used in domestic settings.
How much does PIV installation cost in London?
A standard loft-mounted PIV unit for a house typically costs £400–£700 fully installed in London. A wall-mounted unit for a flat costs £500–£800. Units with an integral heating element for colder properties cost £600–£900. Running costs are very low — typically £10–£30 per year in electricity. We provide a fixed, itemised quote after the initial survey with no obligation to proceed.
Can a PIV system be installed in a flat without a loft?
Yes. Wall-mounted PIV units are specifically designed for flats, apartments, and properties without loft access. They are installed on an internal wall — typically in a hallway or landing — and ducted through to an external wall. They operate on exactly the same principle as a loft unit and are equally effective at reducing condensation and mould in flats.
How long does PIV installation take?
A loft-mounted PIV installation in a house typically takes three to four hours. A wall-mounted flat installation takes two to three hours. There is no major disruption involved — just one ceiling diffuser opening in the hallway and a small external vent. The unit is fully operational the same day.
How long before I see results from a PIV system?
Most homeowners notice less condensation on windows within a few days of installation. The musty smell typically reduces within one to two weeks as stale air is progressively displaced. Mould patches stop growing relatively quickly — they don’t disappear on their own, but they stop spreading and can then be cleaned and treated knowing they won’t immediately return. Full stabilisation of indoor humidity levels usually takes two to four weeks.
Will a PIV system make my home cold?
This is a concern many homeowners raise, particularly in winter. The incoming air is at external temperature, but because PIV systems operate at a very low flow rate — a gentle trickle rather than a draught — the impact on room temperature is minimal in most properties. For properties that are sensitive to incoming air temperature, units with a built-in heating element gently warm the air before it enters the living spaces. We will recommend the appropriate specification for your property during the initial assessment.
Does a PIV unit need regular maintenance?
PIV units require very little maintenance. The main task is an annual filter change, which takes a few minutes and costs a small amount. Some units have an indicator light that signals when the filter needs replacing. There are no moving parts beyond the fan motor, which has a long service life. We also provide ventilation system servicing → for existing units if required.
Is PIV suitable for a property with rising damp or penetrating damp?
PIV addresses condensation-related damp and mould. It is not a treatment for rising damp or penetrating damp, which are structural problems requiring specific remediation. If your property has structural damp as well as condensation, the structural damp should be treated first — after which PIV may still be beneficial to manage ongoing moisture levels. A damp survey will identify which issues are present.
My landlord says the mould is caused by my lifestyle. Could a PIV system help?
This is a very common situation in London rented properties. While tenant behaviour (cooking, drying clothes indoors, showering without ventilation) does contribute to moisture levels, the root issue is usually a property that lacks adequate ventilation for normal residential use. A PIV system provides the base ventilation that the property structurally lacks. Many London landlords install PIV systems to resolve persistent mould complaints and to comply with their legal obligations under the Homes (Fitness for Human Habitation) Act 2018. Read about landlord and tenant rights →
Related Services
- Condensation Control Services →
- Ventilation System Servicing →
- Damp Survey →
- Landlord Services →
- Why ventilation is important in your home →
- How to stop condensation in your loft →
- Damp in London flats →