Is PIV or MVHR better for condensation?

For an existing house with an accessible loft and a whole-home humidity problem, PIV is usually the right answer at £400–£800 installed. MVHR performs better and recovers heat but needs ductwork throughout and a reasonably airtight building, so it mainly suits new build or a substantial refurbishment. MVHR retrofitted into a leaky period property loses much of its benefit.

Do extractor fans on their own stop condensation?

They help, and modern continuous-running (dMEV) fans in the kitchen and bathroom are a strong baseline. But extract only ventilates the room it serves — bedrooms and living rooms with condensation on external walls still need air movement from a whole-house system or from background ventilation such as trickle vents.

Can a PIV unit be fitted in a flat with no loft?

A standard loft-mounted PIV needs a roof void to draw from. Flats without one need a loft-less PIV variant that draws from outside through a wall, or a different approach — usually continuous extract in the wet rooms plus trickle ventilation.

Does more heating fix condensation instead of ventilation?

Only partly. Warmer air holds more moisture and warmer surfaces stay above the dew point longer, so heating helps — but heating without ventilation just carries warmer, wetter air to the next cold surface. The reliable fixes combine heating with ventilation and, where surfaces are cold, insulation.

How disruptive is fitting MVHR to an occupied house?

Very. Retrofitting ductwork to every wet room and habitable room in a finished, occupied property means lifting floors or boxing in runs, and it is often impractical. MVHR is far cheaper and less disruptive when installed during a refurbishment before rooms are finished.

Is PIV or MVHR better for condensation?

For an existing house with an accessible loft and a whole-home humidity problem, PIV is usually the right answer at £400–£800 installed. MVHR performs better and recovers heat but needs ductwork throughout and a reasonably airtight building, so it mainly suits new build or a substantial refurbishment. MVHR retrofitted into a leaky period property loses much of its benefit.

Do extractor fans on their own stop condensation?

They help, and modern continuous-running (dMEV) fans in the kitchen and bathroom are a strong baseline. But extract only ventilates the room it serves — bedrooms and living rooms with condensation on external walls still need air movement from a whole-house system or from background ventilation such as trickle vents.

Can a PIV unit be fitted in a flat with no loft?

A standard loft-mounted PIV needs a roof void to draw from. Flats without one need a loft-less PIV variant that draws from outside through a wall, or a different approach — usually continuous extract in the wet rooms plus trickle ventilation.

Does more heating fix condensation instead of ventilation?

Only partly. Warmer air holds more moisture and warmer surfaces stay above the dew point longer, so heating helps — but heating without ventilation just carries warmer, wetter air to the next cold surface. The reliable fixes combine heating with ventilation and, where surfaces are cold, insulation.

How disruptive is fitting MVHR to an occupied house?

Very. Retrofitting ductwork to every wet room and habitable room in a finished, occupied property means lifting floors or boxing in runs, and it is often impractical. MVHR is far cheaper and less disruptive when installed during a refurbishment before rooms are finished.

PIV vs MVHR vs Extractor Fans for Condensation

Quick answer: For most existing homes with a loft, a positive input ventilation (PIV) unit at £400–£800 installed is the most cost-effective way to control whole-home condensation. Mechanical ventilation with heat recovery (MVHR), at £3,000–£8,000, performs better and recovers heat but suits new build or major refurbishment. Continuous extract fans handle the wet rooms; trickle vents supply the replacement air both of the others rely on.

There is no single "condensation product". Every option does one job well and hits a limit somewhere else. This guide compares them honestly and gives a process for choosing the right combination for a specific property.

The three things any fix has to address

Condensation is the result of an imbalance between how much moisture is in the indoor air, how fast that air is exchanged for drier outdoor air, and how cold the internal surfaces are. A competent fix targets whichever of those is the weak link — and often more than one.

Positive input ventilation (PIV)

A loft-mounted unit draws filtered air from the roof space and gently pushes it into the home through a single central ceiling diffuser, slightly pressurising the property so stale humid air is displaced out through gaps and vents.

Best for: houses and bungalows with an accessible loft and a whole-home humidity problem. The most cost-effective single intervention for most condensation mould.
Typical cost: £400–£800 installed.
Limitations: needs a loft or roof void — flats without one need a loft-less variant. It moves air one way, so it relies on the property having enough leakage or trickle venting for air to escape. It is not a substitute for extract at the source in kitchens and bathrooms.

Mechanical ventilation with heat recovery (MVHR)

A whole-house ducted system continuously extracts stale air from wet rooms and supplies filtered fresh air to living rooms and bedrooms, passing the two airstreams through a heat exchanger so most of the warmth in the outgoing air is recovered.

Best for: new build and substantial refurbishment, where the ductwork can be installed and the building fabric is airtight enough for heat recovery to be worthwhile.
Typical cost: £3,000–£8,000 installed.
Limitations: retrofitting ductwork into an occupied period property is disruptive and often impractical. It only performs well in a reasonably airtight building — in a leaky property much of the benefit is lost. The unit and filters need regular maintenance.

Extractor fans: continuous and intermittent

Continuous mechanical extract (dMEV) — low-wattage fans in the kitchen and bathroom that run continuously at a trickle rate and boost on humidity or occupancy, removing moisture where it is produced rather than after it has spread through the home. A strong baseline upgrade from old intermittent fans. It only ventilates the rooms it serves, and relies on replacement air being able to enter the property.

Intermittent extract fans — standard fans that run while the room is in use. The cheapest first step where a wet room currently has no mechanical extract at all, but they do nothing between uses, so moisture produced overnight or from drying laundry is not addressed. They are frequently found undersized, badly ducted, or wired so tenants can switch them off.

Trickle vents: the piece everyone forgets

Trickle vents are small controllable slot vents in the head of a window or door frame that provide a continuous background supply of outdoor air. They are the "way in" for the replacement air that mechanical extract and PIV both depend on. Since 15 June 2022, Approved Document F requires that replacement windows do not reduce a home's existing ventilation, which in practice means trickle vents on most replacements. They are background ventilation only — not a fix for an active problem by themselves.

Insulation and heating

Where the underlying issue is cold surfaces and thermal bridging, the fix that removes the cause is to raise the temperature of those surfaces: loft, cavity or solid-wall insulation, insulated plasterboard to a specific cold patch, and better heating controls so rooms are actually heated. Solid-wall insulation is a significant cost and, done badly, can move the condensation risk into the wall, so it needs designing rather than just installing.

Dehumidifiers

A dehumidifier manages humidity while it runs and is useful for drying a property out or holding a problem room while permanent work is planned. It does not fix the building defect. A home that needs a dehumidifier running permanently to stay mould-free has an unresolved ventilation, heating or insulation problem. For a landlord, supplying a dehumidifier in place of fixing the property is not a lawful response to a ventilation deficiency.

Matching the fix to the property

A few common situations and where they usually land:

Three-bed semi, sealed replacement windows with no trickle vents, mould in both children's bedrooms. Fit trickle vents, upgrade the bathroom and kitchen fans to continuous, and add a PIV unit in the loft. Total is usually well under £1,500 and resolves the whole house.
Ground-floor flat, no loft, bathroom mould and streaming kitchen windows. Continuous extract (dMEV) in both wet rooms, trickle vents to the main habitable rooms, and a check that the extract is actually ducted to outside rather than into a void.
Solid-wall Victorian terrace, cold north-facing bedroom wall with mould behind the wardrobe. This is a cold-surface problem first. Internal wall insulation or insulated plasterboard to that wall, designed to manage vapour, plus background and extract ventilation.
New build or full refurbishment. Specify MVHR from the start. The ductwork is cheap to install before the rooms are finished and the airtight fabric makes heat recovery worthwhile.

What a good contractor does before quoting

A competent installer takes humidity readings, checks the existing fans and their ducting, looks at insulation and window ventilation, and asks about the pattern of the mould — before recommending anything. A single-product quote against a whole-home problem, with no diagnosis, is the warning sign to walk away from. If a survey is needed, an independent damp survey costs £200–£400 and is not tied to selling a treatment.

How to choose

Diagnose the weak link — moisture load, air exchange, cold surfaces, or a combination. A humidity reading, a check of the existing fans, and a look at insulation and window ventilation usually tell you.
Fix extraction at the source — working, correctly-sized extract in every kitchen and bathroom, ducted to outside. Upgrade old intermittent fans to continuous where practical.
Restore background ventilation — open or fit trickle vents, unblock airbricks, undercut internal doors.
Add whole-house ventilation if needed — PIV for a house with loft access; MVHR for new build or substantial refurbishment.
Warm the cold surfaces — insulate and make the property affordable to keep at a steady temperature.

For firm cost breakdowns see how much condensation control costs. To get a survey and quotes, find a verified condensation specialist.

PIV vs MVHR vs extractor fans: which ventilation system stops condensation?