Best PIV units for landlords 2026: stop condensation mould

Awaab’s Law — the implied tenancy term in section 10A of the Landlord and Tenant Act 1985, inserted by section 42 of the Social Housing (Regulation) Act 2023 and given effect by the Hazards in Social Housing (Prescribed Requirements) (England) Regulations 2025 (SI 2025/1042) — came into force for the social rented sector on 27 October 2025. Under this framework, registered providers of social housing must respond to hazards within five statutory deadlines, structured across two tracks.

For emergency hazards, landlords have 24 hours from awareness to investigate AND make safe — the obligation runs in calendar hours, including weekends and bank holidays.

For significant hazards (which include all damp and mould hazards within the Phase 1 scope), the further deadlines apply: 10 working days to investigate; 3 working days to provide a written summary of the findings of the investigation (Reg 9 of SI 2025/1042); 5 working days to complete safety works; and, for any additional preventative works, a 5-working-day default to begin (Reg 13(2)) with a 12-week (84 calendar day) backstop only where beginning within 5 working days is not reasonably practicable (Reg 13(3)(b)) — both measured from the day after the day on which the investigation is completed, and completion required within a reasonable period (Reg 13(4)).

Phase 1 (in force since 27 October 2025) covers two categories: damp and mould as significant hazards, and all emergency hazards across all HHSRS hazard categories — including dangerous electrical faults, major leaks, severe penetrating damp, and water leaks causing electrical safety risks. Phase 2 is due to start on 30 November 2026, subject to Parliament approving the regulations. It extends the significant-hazard track to excess cold, excess heat, falls, structural collapse and falling elements, fire and explosions, electrical hazards, and domestic hygiene including pests.

The Renters’ Rights Act 2025 (Royal Assent 27 October 2025) is also relevant. Since 1 May 2026, the maximum civil penalty for failure to comply with an Improvement Notice (under section 249A of the Housing Act 2004 and section 23 of the Housing and Planning Act 2016) has risen from £30,000 to £40,000. The Act also allows Awaab’s Law to be extended to the private rented sector, but that needs further regulations and no start date has been set. Installing effective ventilation now is a cost-effective way to get ahead of the regulatory direction of travel for both social and private landlords.

PIV directly addresses the most common cause of residential mould: excess moisture from cooking, showering, drying clothes, and breathing. By maintaining a constant airflow, PIV prevents moisture from settling on cold surfaces. It is one of the most practical interventions a landlord can install — particularly in pre-2000 housing stock that was not designed with modern ventilation standards in mind.

A positive input ventilation unit pushes a steady supply of filtered air into the home, usually through a ceiling diffuser on the landing or in the hallway. That gentle positive pressure moves the damp air from cooking, washing and breathing out through the gaps in the building, so less of it settles on cold walls and windows. Unlike an extractor fan, which runs only when switched on, a PIV unit runs all the time at low speed.

Loft-mounted units are the most common. They sit in the loft and draw in air from the roof space. Many have a small heater that takes the chill off the air in winter.

Wall-mounted units are for flats and homes without a loft. They draw air from outside through a duct in the wall.

Units with humidity sensing speed up when the air gets damp, for example after a shower, and slow down again afterwards.

If an investigation finds that poor ventilation is causing the damp, dealing with that cause is the landlord’s job. Once a unit is fitted, servicing it is generally the landlord’s responsibility too. Give tenants a short written note on what it does and ask them not to switch it off or cover the diffuser.

PIV suits older properties with natural air leakage, properties suffering general condensation across multiple rooms, and any situation where a whole-house solution is needed at relatively low cost. It covers most pre-2000 UK housing stock — the bulk of rental properties.

Mechanical extract fans (bathroom extractors, continuous mechanical extract ventilation / cMEV) belong where moisture is concentrated: in bathrooms, in kitchens and in utility rooms. Building Regulations Approved Document F requires extract ventilation in these rooms as a minimum. Treat extract as complementary to PIV, not a replacement.

MVHR systems, which supply and extract through a heat-exchanger ducted network, suit airtight new-build properties designed to Part L standards. They are typically £3,000–£7,000 installed and impractical to retrofit into most existing rentals. For older housing stock, PIV is the practical choice.

In many cases, the optimal landlord strategy is a PIV unit in the central hallway combined with intermittent extract fans in wet rooms.

Two things pair well with a PIV unit: a humidity-controlled fan for the bathroom, and a hygrometer to record humidity before and after installation for the case file. Both links below are affiliate links.