Understanding the Different Types of Extractor Fans (and PIV Units)

Your Guide to Effective Moisture Control, Airflow & Compliance

From fogged-up bathrooms to musty-smelling hallways and recurring black mould — poor ventilation is one of the most common causes of property deterioration, tenant complaints, and failed inspections.

At Switch Electrical & Mechanical Services Ltd, we install compliant, effective extractor systems across the North East. Whether you’re planning a new bathroom, managing rental stock, or upgrading a tired WC fan, it’s vital to choose the right solution. Below, we break down the most common extractor fans and whole-property systems — including PIV (Positive Input Ventilation) units — so you can make the right call.

⸻

1. Axial Extractor Fans (Standard Wall Fans)

Best For: Small bathrooms, WCs, en-suites or kitchens with a direct external wall. Description: The most basic and commonly seen fan. Air is pulled straight through the fan and out via a grille on the wall. Features: • Surface-mounted • Typically activated by a light switch or pull cord • Suits short duct runs (under 1.5 metres) Limitations: • Unsuitable for rooms without an external wall • Weak performance if duct run is long or obstructed

⸻

1. Centrifugal Fans (High Pressure)

Best For: Internal bathrooms, utility rooms, or long duct routes. Description: These fans use a turbine-style impeller, allowing them to push air through longer or more complex ducting — typically via ceilings or boxed pipe runs. Features: • Higher pressure than axial fans • Can duct air up to 10 metres • Often ceiling-mounted and routed to soffit or roof terminals

⸻

1. Timer Overrun Fans

Best For: Properties where users may not leave the fan running long enough — e.g. rentals or communal bathrooms. Description: After switching off the light, the fan continues running for a set duration (commonly 5–30 mins) to clear remaining moisture. Benefits: • Helps reduce condensation and mould • No user input required • Compliant with modern ventilation standards

⸻

1. Humidity Sensor Fans

Best For: High-moisture areas such as en-suites, laundry rooms, and steamy bathrooms. Description: These fans automatically activate when humidity exceeds a set percentage (e.g. 65%) and stop once levels return to normal. Benefits: • Fully automated — no switches required • Helps prevent black mould • Saves energy by only running when needed

Combined Humidity & Timer Overrun Fans Some extractor fan models are designed to combine both a humidity sensor and a timer overrun function in a single unit. This means the fan will automatically switch on when humidity levels rise (for example, during a shower) and then continue to run for a set period after the humidity has reduced. This dual feature provides a more thorough approach to moisture control — ensuring that both immediate steam and lingering condensation are effectively dealt with. These combined units are ideal for busy family bathrooms and rental properties, where consistent performance and user‑independent operation are important.

⸻

1. In-Line Fans (Loft or Void Mounted)

Best For: High-spec bathrooms, flats with no wall access, or when silent operation is desired. Description: These fans are mounted remotely in lofts or ceiling voids, with ducting connecting to discreet ceiling grilles. Benefits: • Extremely quiet • Visually discreet • Can serve multiple rooms (dual-input designs)

⸻

1. PIV Systems (Positive Input Ventilation)

Best For: Whole-property airflow in homes suffering from persistent condensation, damp, or mould. Description: PIV units are usually loft-mounted systems that gently introduce filtered, fresh air into the home. This air creates a slight positive pressure, forcing out stale, moist air through natural leakage points or trickle vents. How They Work: • Draw air from the loft (or outside in flat systems) • Filter and temper the air • Push it into the landing or central area • Displace old, moisture-laden air from the property Benefits: • Tackles whole-house condensation, not just bathrooms • Helps eliminate mould spots and musty smells • Improves overall air quality • Low energy consumption • Can help reduce radon levels in certain regions Ideal For: • Properties with no trickle vents or poor extraction • Older homes with solid walls or blocked chimneys • Flats and social housing suffering repeated damp issues

Installation Tip: PIV units should be installed centrally — typically in a landing ceiling. At Switch, we follow manufacturer recommendations for airflow paths, filters, and correct power supply setup.

⸻

Need Help Choosing the Right Fan or System?

Whether you’re dealing with damp complaints from tenants, modernising a bathroom, or exploring whole-house ventilation for compliance — we’re here to help. Our NICEIC-accredited engineers offer expert advice and tailored installations throughout the North East.

📞 Call us on 0191 905 2723 📧 Email: switchtoday@mail.com 📱 Instagram: @switchelectrical_

Switch Electrical & Mechanical Services Ltd Delivering Exceptional Quality and Expertise in Electrical Contracting Across the North East

Frequently Asked Questions (North East UK)

Who is responsible for fixing electrical faults in my rented home? In the UK, your landlord is legally responsible for maintaining the electrical wiring, sockets, and fixed fittings in your home. If you discover a fault, such as a sparking socket or a constantly tripping RCD, you should report it to your landlord or letting agent immediately. Switch Electrical & Mechanical Services works with dozens of letting agents across Newcastle to provide rapid fault-finding services.

Why does my fuse box keep tripping when I use the shower? A constantly tripping RCD or MCB is a sign that there is a fault on the circuit, often caused by water ingress, an overloaded circuit, or a failing appliance (like a damaged shower heater or a blocked mineral bead shower head causing resistance). Do not repeatedly reset the breaker. Contact your landlord or property manager to arrange an inspection by a qualified electrician in the North East.

Are tenants responsible for changing lightbulbs? Generally, yes. Tenants are responsible for basic day-to-day maintenance, such as changing accessible lightbulbs. However, if a fitting is broken, flickering constantly despite a new bulb, or emitting a burning smell, this is a structural fault that your landlord must address using a certified electrical contractor.