What are the UK Building Regulations for extractor fans?

Under Part F of the Building Regulations, a new bathroom must have an extraction rate of at least 15 Litres per second (L/s). For a kitchen with a wall-mounted fan, the minimum is 30 L/s, and for a utility room, it is 30 L/s.

What is the difference between an Axial and a Centrifugal fan?

Axial fans move air directly through the blades and are best for short ducting runs (under 1.5m). Centrifugal fans are much more powerful and can push air through long ducting runs with several bends, making them ideal for flats or internal bathrooms where the vent is far from the outside wall.

How do I calculate Litres per second from m³/h?

To convert Cubic Metres per Hour (m³/h) to Litres per Second (L/s), you divide the m³/h figure by 3.6. For example, a fan rated at 54 m³/h is equivalent to 15 L/s.

Do I need a fan if I have a window?

In most modern UK renovations or new builds, an extractor fan is mandatory in 'wet rooms' (bathrooms and kitchens) even if there is an openable window. This ensures consistent moisture removal regardless of the weather.

What are the UK Building Regulations for extractor fans?

Under Part F of the Building Regulations, a new bathroom must have an extraction rate of at least 15 Litres per second (L/s). For a kitchen with a wall-mounted fan, the minimum is 30 L/s, and for a utility room, it is 30 L/s.

What is the difference between an Axial and a Centrifugal fan?

Axial fans move air directly through the blades and are best for short ducting runs (under 1.5m). Centrifugal fans are much more powerful and can push air through long ducting runs with several bends, making them ideal for flats or internal bathrooms where the vent is far from the outside wall.

How do I calculate Litres per second from m³/h?

To convert Cubic Metres per Hour (m³/h) to Litres per Second (L/s), you divide the m³/h figure by 3.6. For example, a fan rated at 54 m³/h is equivalent to 15 L/s.

Do I need a fan if I have a window?

In most modern UK renovations or new builds, an extractor fan is mandatory in 'wet rooms' (bathrooms and kitchens) even if there is an openable window. This ensures consistent moisture removal regardless of the weather.

Extractor Fan Calculator

Ensure your home meets UK ventilation standards.

Width (m)

Depth (m)

Height (m)

Room Type (UK Regs)

Required Capacity

Selection Tip: Always buy a fan with a slightly higher capacity than the minimum required. Factors like long ducting runs, bends in the pipe, and wind resistance can reduce the effective extraction rate of a fan by up to 30%.

Fresh Air: The UK Ventilation Guide

Air Changes Per Hour

Condensation and mould are the biggest threats to a UK home's structural integrity and occupant health. A correctly sized extractor fan removes moisture-laden air before it can settle on cold surfaces.

Our **extractor fan calculator** uses your room dimensions to ensure your new fan meets the minimum 'Air Changes per Hour' required by **Part F Building Regulations**.

Minimum Extraction Rates

Bathroom / Shower15 Litres/sec

Kitchen (Wall Fan)30 Litres/sec

Utility Room30 Litres/sec

Ducting & Resistance

A fan's performance on the box is its 'free air' rating. In reality, every metre of ducting and every 90-degree bend creates resistance (back pressure) that slows the air down.

If you are venting through a long duct in the loft, you must choose a fan with a high 'Static Pressure' rating—typically a centrifugal or mixed-flow fan—rather than a basic axial fan, which will fail to move air over long distances.

Heat Recovery

Standard fans pull warm air out of your house. Modern 'dMVHR' (Single Room Heat Recovery) fans extract moisture but use a ceramic heat exchanger to pre-warm the fresh air coming in, saving on heating bills.

IP Ratings & Zones

Fans installed directly above a shower or bath (Zone 1) must be at least **IPX4** rated or **SELV** (Safety Extra Low Voltage) to ensure electrical safety in wet environments.

Pro Tip: The Undercut Door

An extractor fan cannot pull air out of a room if fresh air cannot get in. Ensure there is at least a **10mm gap** under your bathroom or kitchen door. Without this 'undercut', the fan will create a vacuum and its efficiency will drop by up to 50%.

Ventilation & Part F FAQ

Project Disclaimer

Electrical work in bathrooms is 'Notifiable' under Part P of the Building Regulations. All fans should be installed by a qualified electrician and tested with a vane anemometer to ensure the actual L/s output meets the design requirements.