"The Vent-Axia PoziDry Pro is the most widely installed loft-mounted PIV unit in UK residential properties, and for good reason. It's well-built, genuinely quiet, and effective at controlling condensation and mould in most UK homes. The heater model (476311) is the one to choose for most properties."
- Geoff Smith - Ventilation Expert
Key Takeaways
- Loft-mounted positive input ventilation (PIV) unit — installs in one day without major building work
- Three models available: standard (476310, £276), heater (476311, £363), and multi-storey heater (476312, £512)
- Max airflow of 176 m³/h (standard and heater) — suitable for most UK semi-detached and detached homes
- F7-rated filter removes dust, pollen and PM2.5 particles — lasts up to 5 years before replacement
- Lo-Carbon EC motor keeps annual running costs low — typically £10–£20/year
- 5-year manufacturer warranty as standard
What Is the Vent-Axia PoziDry Pro?
The PoziDry Pro is a Positive Input Ventilation (PIV) unit — a loft-mounted fan that draws fresh filtered air from the loft void and distributes it into the home through a single ceiling diffuser, typically installed in the first-floor hallway. By gently pressurising the home, it pushes humid stale air out through natural gaps in the building fabric, keeping relative humidity low and preventing the condensation that leads to mould growth.
PIV is not the same as an extractor fan or an MVHR system. It doesn't extract air from specific rooms — it works by changing the pressure balance across the whole home. For most existing UK homes with persistent condensation or mould problems, particularly those without adequate trickle vents or whole-home ventilation, a PIV unit is one of the most cost-effective and lowest-disruption fixes available. For a full explanation of how PIV works and whether it's right for your property, see our complete PIV guide.
PoziDry Pro Model Comparison: 476310 vs 476311 vs 476312
There are three variants in the current PoziDry Pro range. The differences come down to whether you need a heater and the size of your property.
| Model | Max Airflow | Best For | Price (eFans) |
|---|---|---|---|
| PoziDry Pro SKU 476310 |
176 m³/h | Well-insulated homes / South of England — no heater | £276.04 |
| PoziDry Pro with Heater SKU 476311 |
176 m³/h | Most UK homes — recommended as standard (+4°C heater) | £363.80 |
| PoziDry Pro Multi Storey with Heater SKU 476312 |
216 m³/h | Larger homes, 3+ storeys — includes speed controller | £512.99 |
Which model should you choose?
For the majority of UK homes — a standard semi-detached or detached house with up to 4 bedrooms — the 476311 heater model is the right choice. The heater warms loft air by 4°C before it enters the living space, which is important in winter when loft temperatures can drop well below the ambient indoor temperature and cold incoming air would otherwise cause discomfort.
The unheated 476310 is only recommended for well-insulated modern homes in the South of England where loft temperatures rarely drop significantly. The 476312 Multi Storey variant is for larger or taller properties where a higher maximum airflow is needed to adequately ventilate all floors from a single unit.
Full Specifications (476311 — Heater Model)
| Specification | Detail |
|---|---|
| Max airflow | 176 m³/h |
| Motor type | Lo-Carbon EC (electronically commutated) |
| Heater output | +4°C temperature boost |
| Filter class | F7 (traps PM2.5, pollen, fine dust) |
| Filter life | Up to 5 years (subject to air quality) |
| Noise level | Ultra-low — anti-vibration mounting legs |
| Warranty | 5 years (Vent-Axia) |
| Property coverage | Up to 150m² floor area |
| Installation location | Loft — above first-floor hallway |
| Diffuser connection | Single ceiling diffuser (included) |
| Included in box | Unit, leg supports, F7 filters, jubilee clips, white extract valve |
Installation: What's Involved?
The PoziDry Pro is designed to be installed by a competent electrician or ventilation engineer in a single visit. No structural work is required — the unit sits in the loft on its adjustable anti-vibration legs, connected to the hallway ceiling below via a short duct drop and the included diffuser grille. The electrical connection requires a fused spur to 240V. Most installations are completed in three to five hours.
The key installation requirements are:
- Accessible loft void with sufficient headroom to place the unit above the hallway (ideally over a first-floor landing or hallway ceiling)
- A clear duct path from the unit down through the ceiling to the diffuser position — typically a 204×60mm flat duct drop or 100mm round
- A 240V fused spur within the loft void
- Loft insulation should not obstruct the unit's air intake — a loft installation kit (available separately) can raise the unit above deep insulation if needed
It is not recommended to install a PIV unit yourself unless you are competent with both electrical work and ductwork — the electrical connection in particular should be carried out by a qualified electrician.
Running Costs
The PoziDry Pro uses Vent-Axia's Lo-Carbon EC motor, which is designed for continuous low-speed operation at very low wattage. At typical operating speeds the unit draws only a few watts — annual electricity costs are estimated at £10–£20 per year depending on energy tariff and usage settings. The heater element uses more power when active, but operates on a thermostat and only engages when incoming air is cold enough to require it.
Filter replacement is the main ongoing cost. Replacement F7 filters are available from eFans and should be changed every two to five years depending on your local air quality. Replacement filters for the PoziDry Pro are available in our Vent-Axia accessories range.
Does the PoziDry Pro Actually Work?
PIV is a proven technology with decades of UK installation history, and the PoziDry Pro is the market-leading product in the category. It is effective at controlling condensation-related mould in most existing UK homes — particularly older properties that rely on infiltration and natural ventilation rather than purpose-designed whole-home mechanical ventilation. Most users report a noticeable improvement in condensation within days to a couple of weeks of installation.
It is worth being clear about what PIV does and doesn't do. It is not an air purifier — while the F7 filter does capture PM2.5 particles and pollen, the unit is not designed or marketed as a primary air quality improvement device. It is specifically a condensation and mould control solution, and in that role it performs well. For properties with severe structural dampness (rising damp, penetrating damp) rather than condensation, PIV alone will not resolve the underlying issue.
Frequently Asked Questions
How long does it take for the PoziDry Pro to work?
Most homes see a reduction in condensation on windows and cold surfaces within a few days. Surface mould that has already formed will not disappear automatically — it needs to be cleaned first — but once the PoziDry Pro has stabilised indoor humidity, mould regrowth is typically prevented. Allow two to four weeks to fully assess the unit's impact on your home's humidity levels.
What is the difference between the 476310 and the 476311?
The 476310 is the standard PoziDry Pro without a heater. The 476311 adds an integrated heater that warms incoming loft air by approximately 4°C before it enters the living space. For most UK homes, particularly those in the Midlands, North of England, Scotland or Wales, the heater model (476311) is strongly recommended. Unheated loft air in winter can be significantly colder than the indoor temperature, making unheated PIV uncomfortable in cooler climates. The 476311 is £87 more expensive than the 476310 — in most cases, it's money well spent.
Can I install a PoziDry Pro myself?
The physical positioning of the unit and the duct connection can be managed by a competent DIYer, but the electrical connection (fused spur to 240V) must be carried out by a qualified electrician. Most installation companies offer a full supply-and-fit service. If you're considering DIY installation, ensure you have adequate access to the loft and a clear path for the duct drop before purchasing.
How often do PoziDry Pro filters need replacing?
Vent-Axia recommends replacing the F7 filter every two to five years. In areas with higher levels of airborne particulates — near busy roads, or in rural areas with significant agricultural activity — filters may need changing more frequently. Replacement filters are available from eFans in our Vent-Axia accessories range.
Is the PoziDry Pro suitable for a bungalow?
Yes — bungalows are well suited to PIV because the entire property is single-storey and a single diffuser in the hallway ceiling can serve the whole floor effectively. For a bungalow, the standard 476311 heater model is typically sufficient regardless of size.
What is the PoziDry Pro 476312 Multi Storey?
The 476312 is a higher-capacity version of the PoziDry Pro heater unit with a maximum airflow of 216 m³/h (versus 176 m³/h on the 476311). It is designed for larger properties — typically homes with three or more storeys, or properties where a single diffuser needs to distribute sufficient fresh air across a larger floor area. It includes an integrated speed controller. At £512, it is significantly more expensive than the 476311, and is not necessary for most standard UK semi-detached or detached houses.
Where can I buy the Vent-Axia PoziDry Pro?
All three PoziDry Pro models are available from eFans with next day delivery. The heater model (476311) is our recommended choice for most UK homes: