The four main options in the UK are extract ventilation, positive input ventilation (PIV), mechanical ventilation with heat recovery (MVHR), and decentralised units. The right choice depends on your property's age, airtightness, layout, and what problem you're actually trying to solve.
The Four System Types
Extract ventilation removes stale, moisture-laden air from bathrooms, kitchens, and utility rooms. Intermittent fans run on demand; continuous mechanical extract (MEV) runs at low speed constantly with a boost mode for high-humidity periods. Extract-only systems don't supply fresh air, which can cause negative pressure and draughts through gaps in the building fabric. Cost: £500-£1,500 installed.
Positive input ventilation (PIV) draws filtered fresh air in from outside - typically via a loft-mounted unit - and distributes it gently through the property, pushing stale air out through natural ventilation paths. It's effective against condensation and mould in older, leakier properties. In very airtight modern homes it's less effective, and the incoming air needs warming in winter, which adds slightly to heating costs. Cost: £800-£2,000 installed.
Mechanical ventilation with heat recovery (MVHR) extracts stale air and supplies fresh air simultaneously, passing both through a heat exchanger that transfers up to 90% of the heat from outgoing air to the incoming supply. The result is continuous filtered fresh air with minimal heat loss. MVHR requires a well-designed ductwork layout and suits properties built or renovated to high airtightness standards. It's the standard choice for new builds and deep retrofits. Cost: £3,000-£8,000+ depending on property size and ductwork complexity.
Decentralised units are individual wall-mounted units that ventilate single rooms without ductwork. Many models include a small heat exchanger. They suit room-by-room upgrades, properties where running ductwork is impractical, or mixed-use buildings with varying ventilation needs. Cost: £400-£1,200 per unit installed.
Matching System to Property
| Property type | Typical best fit |
| Pre-1920s traditional construction | PIV or targeted extract |
| 1930s-1990s mixed construction | MEV or decentralised |
| Modern construction (2000s+) | MVHR |
| New build or deep retrofit | MVHR |
| Small flat, limited space | Decentralised or compact MEV |
| Large house, high airtightness | MVHR |
If your main problem is condensation in a bathroom or kitchen, an intermittent extract fan with a humidity sensor is often the most practical fix. If you have persistent whole-house damp, mould on cold walls, or stuffy air throughout, you need a whole-house system.
Running Costs and Energy Impact
Extract systems and PIV have low electricity costs - typically £20-£50 per year to run - but both can increase heating costs. Extract systems pull heated air out; PIV brings cool air in. In a poorly insulated property, either can add £100-£200 to annual heating bills depending on how hard they run.
MVHR's heat recovery offsets most of that penalty. A well-designed MVHR system in a high-airtightness property typically costs £50-£100 per year to run and saves significantly more in reduced heat loss compared to passive or extract ventilation. The payback case is strongest in new builds and deep retrofits where the building envelope is already tight.
Decentralised units with heat recovery sit between the two - better than extract-only, less comprehensive than whole-house MVHR.
Installation Considerations
MVHR requires ductwork running through the property - usually in ceiling voids, loft space, or purpose-built service zones. Retrofitting ductwork in an occupied home is disruptive and sometimes impractical depending on construction type. This is why MVHR is far easier to design into a new build or major renovation than to add later.
PIV needs loft space for the central unit and adequate loft insulation beneath it - a PIV unit in a cold, uninsulated loft blows cold air into the property rather than temperate fresh air.
Extract fans and decentralised units need only a hole through an external wall. Installation is straightforward and causes minimal disruption.
Noise is worth checking. MVHR systems typically operate at 25-35 dB at normal flow rates - quieter than a fridge. PIV units are near-silent. Extract fans vary considerably by model; cheaper fans can be significantly louder than premium equivalents at the same flow rate.
Building Regulations
Part F of the Building Regulations sets minimum ventilation standards for new builds and properties undergoing certain types of renovation in England. Changes to Part F in 2021 tightened requirements, particularly around whole-house ventilation in new builds and extensions. If your project triggers building regulations, your ventilation system needs to comply - your installer or building control officer can confirm what applies to your specific work.
FAQ
My home has a condensation and mould problem. Which system will fix it? Start by identifying where the moisture comes from. If it's concentrated in bathrooms and the kitchen, extract ventilation with humidity-sensing fans addresses it at the source. If mould appears on external walls throughout the house, particularly in corners and behind furniture, you likely have a whole-house humidity problem - PIV or MEV will help more. A surveyor can confirm the cause before you commit to a system.
Is MVHR worth the extra cost for a retrofit? In a modern, well-insulated property it usually is, particularly if you're planning other renovation work at the same time. The heat recovery benefit is most significant when the building fabric is already good. In an older, draughtier property, the heat exchanger efficiency drops because uncontrolled air infiltration bypasses the system - PIV or MEV will deliver better value in that context.
Can I install ventilation myself? Extract fans are within DIY capability for anyone comfortable with basic electrical work. Anything involving ductwork, whole-house system design, or electrical work in bathrooms requires a competent installer. MVHR design is a specialist area - an incorrectly balanced system underperforms significantly and can cause noise and air quality issues.
How often does a ventilation system need servicing? MVHR filters need replacing every 6-12 months depending on local air quality and usage. The heat exchanger itself requires annual checking. PIV filter replacement is typically annual. Extract fans need periodic cleaning to maintain flow rates. All systems benefit from an annual check of flow rates against commissioning values - performance drops quietly over time without one.
Contact us for a free assessment of your property's ventilation needs. We'll respond within one working day.