Part F Ventilation Calculator 2026 | UK Building Regulations

Part F Ventilation Calculator 2026

Calculate Ventilation Requirements for UK Buildings

Compliant with Building Regulations Approved Document F

Adequate ventilation is essential for health, comfort, and building performance. Building Regulations Approved Document F sets minimum ventilation standards for all UK buildings updated in 2022. Our Part F ventilation calculator determines extract rates, background ventilation, and purge ventilation requirements for dwellings and non-domestic buildings in 2026.

Proper ventilation removes moisture, pollutants, and odours while maintaining indoor air quality. Requirements vary by room type, building use, and ventilation strategy. This calculator incorporates CIBSE guidance and current Building Regulations to ensure compliance with indoor air quality standards.

💨 Ventilation Rate Calculator

Calculate minimum ventilation requirements for your project

Building Details

Building Type

Room Type

Floor Area (m²)

Number of Bedrooms (Dwelling)

Ventilation Strategy

Required Extract Rate

0 l/s

Continuous/Intermittent extraction

Ventilation Requirements

Background Ventilation

0 mm²

Purge Ventilation

0 m²

Whole Dwelling Rate

0 l/s

Air Changes/Hour

0 ACH

Equipment Specifications

Extract Fan Type Centrifugal/Axial

Fan Power Rating 0.3 W/(l/s)

Duct Diameter 100-125mm

Trickle Vent Size -

Building Control Approval Required

Compliance Notes

Part F Compliance Yes

Noise Level Limit < 30 dB (bedrooms)

Commissioning Required & Certificate

Part F Ventilation Requirements 2026

Building Regulations Approved Document F (Ventilation) ensures adequate ventilation to limit moisture, pollutants, and maintain indoor air quality. Updated in 2022, Part F sets specific requirements for extract ventilation, background ventilation, and purge ventilation across all building types.

Minimum Extract Ventilation Rates - Dwellings

Room Type	Intermittent Extract (l/s)	Continuous Extract (l/s)	Boost Duration
Kitchen	30 l/s (adjacent to hob)	13 l/s	30 minutes overrun
Utility Room	30 l/s	8 l/s	30 minutes overrun
Bathroom (with bath/shower)	15 l/s	8 l/s	15 minutes overrun
Toilet (separate)	6 l/s	6 l/s	15 minutes overrun
Shower Room (no bath)	15 l/s	8 l/s	15 minutes overrun

Kitchen

Intermittent Extract 30 l/s

Continuous Extract 13 l/s

Overrun 30 minutes

Bathroom (with bath/shower)

Intermittent Extract 15 l/s

Continuous Extract 8 l/s

Overrun 15 minutes

Toilet (separate)

Extract Rate 6 l/s

Overrun 15 minutes

Whole Dwelling Ventilation Rates

Continuous whole dwelling ventilation provides background air supply throughout the dwelling. Part F 2022 requires minimum whole dwelling ventilation based on floor area and number of bedrooms.

Formula-Based Calculation

Whole Dwelling Rate = 0.3 l/s per m² of floor area

Whole Dwelling Rate whichever is greater:

• 1 bedroom: 13 l/s

• 2 bedrooms: 17 l/s

• 3 bedrooms: 21 l/s

• 4 bedrooms: 25 l/s

• 5+ bedrooms: 29 l/s

Example: 3-Bed House (100m²)

Floor Area Method: 100m² × 0.3 = 30 l/s

Bedroom Method: 3 beds = 21 l/s

Required Rate: 30 l/s (use higher value)

This ensures adequate fresh air supply throughout the entire dwelling continuously.

Ventilation Strategies

System 1: Background ventilators + intermittent extract fans

System 3: Continuous MEV (Mechanical Extract)

System 4: Continuous MVHR (with Heat Recovery)

PIV: Positive Input Ventilation (loft-based)

Background Ventilation Requirements

Background ventilation provides continuous low-level air supply through trickle vents in windows or wall vents. Part F requires specific equivalent areas for habitable rooms when using natural or intermittent extract ventilation systems.

Room Type	Equivalent Area (mm²)	Typical Vent Size	Notes
Habitable Rooms (Living/Bedroom)	8,000 mm²	300mm slot vent	Controllable, secure when closed
Kitchens	4,000 mm²	150mm slot vent	If mechanical extract present
Bathrooms/Toilets	Not required	-	Extract ventilation sufficient
Utility Rooms	4,000 mm²	150mm slot vent	Optional if mechanical extract

Habitable Rooms

Equivalent Area 8,000 mm²

Typical Vent 300mm slot

Kitchens

Equivalent Area 4,000 mm²

Typical Vent 150mm slot

Purge Ventilation Requirements

Purge ventilation allows rapid air exchange for cooling and removing high concentrations of pollutants. Typically provided by opening windows, Part F requires purge ventilation equivalent to 1/20th of the floor area.

✓ Purge Ventilation Formula:

Openable Area = Floor Area ÷ 20

20m² bedroom: Requires 1.0m² openable window area
30m² living room: Requires 1.5m² openable window area
Typical window: 1200mm × 900mm = 1.08m² when fully open
NOT required: In rooms without habitable use (hallways, stairs)
Opening mechanism: Must be easily accessible and operable

Ventilation System Types

Part F recognizes four main ventilation system types for dwellings. System selection depends on building design, energy performance targets, and budget. Each system has specific design requirements and performance standards.

System 1: Background + Intermittent Extract

Components: Trickle vents + extract fans

Extract Fans: Kitchen 30 l/s, Bathroom 15 l/s

Background: 8,000mm² per habitable room

Cost: Most economical £500-1,200

Best for: Small dwellings, retrofits, tight budgets

System 3: Continuous MEV

Components: Central extract unit + ductwork

Operation: 24/7 low rate + boost function

Air Supply: Background vents 8,000mm²

Cost: Moderate £1,500-3,000 installed

Best for: New builds, flats, consistent extraction

System 4: MVHR

Components: Heat recovery unit + supply/extract ducts

Operation: Continuous balanced ventilation

Heat Recovery: 85-95% efficiency

Cost: Premium £3,500-7,000 installed

Best for: Passive House, low energy homes, airtight construction

PIV - Positive Input Ventilation

Components: Loft-mounted fan + diffuser

Operation: Pressurizes dwelling, forces stale air out

Air Supply: Filtered fresh air from loft

Cost: Affordable £600-1,500 installed

Best for: Retrofit, condensation control, simple installation

Specific Fan Power (SFP) Requirements

Part F limits energy consumption of ventilation systems by setting maximum Specific Fan Power (SFP) values. SFP measures electrical power consumed per litre/second of air delivered, expressed in W/(l/s).

⚡ Maximum SFP Limits 2026:

Intermittent Extract Fans: 0.5 W/(l/s) maximum
Continuous MEV Systems: 0.4 W/(l/s) maximum (whole system)
MVHR Systems: 1.5 W/(l/s) maximum (supply + extract combined)
Calculation: SFP = Fan Power (W) ÷ Air Flow Rate (l/s)
Example: 15W fan delivering 30 l/s = 0.5 W/(l/s) ✓ Compliant
Penalty: High SFP systems fail Part F and increase SAP/SBEM ratings

Noise Level Limits

Ventilation systems must not create excessive noise that affects occupant comfort. Part F Section 1.30 sets maximum noise levels for continuous ventilation systems measured in the room being ventilated.

Room Location	Maximum Noise Level	Measurement Method
Living Rooms & Bedrooms	30 dB LAeq,T	Measured 1m from diffuser/grille
Other Habitable Rooms	35 dB LAeq,T	Measured 1m from diffuser/grille
Bathrooms/Toilets/Kitchens	45 dB LAeq,T	Measured 1m from extract terminal
Boost Mode (Intermittent)	No limit specified	Temporary operation acceptable

Living Rooms & Bedrooms

Maximum Noise 30 dB

Bathrooms/Kitchens

Maximum Noise 45 dB

Commissioning and Testing Requirements

All mechanical ventilation systems must be commissioned and tested to verify performance. Part F requires commissioning certificates for Building Control approval, showing actual measured airflow rates match design specifications.

📋 Commissioning Requirements:

Airflow Testing: Measure extract/supply rates at each terminal with calibrated anemometer
System 1 (Intermittent): Test each fan individually - kitchen 30 l/s, bathroom 15 l/s
System 3 (MEV): Test continuous background rates and boost rates at each extract point
System 4 (MVHR): Balance supply/extract flows, verify heat recovery efficiency, check filter status
Noise Testing: Verify maximum noise levels not exceeded in habitable rooms
Documentation: Provide homeowner manual with maintenance instructions and filter replacement schedule
SAP Calculations: Final SAP/SBEM must reflect as-built ventilation system performance

Common Ventilation Failures and Solutions

Inadequate ventilation causes condensation, mould growth, poor air quality, and Building Control failures. Understanding common issues ensures compliant installations that perform effectively long-term.

Insufficient Extract Rates

Issue: Fan undersized or installed incorrectly

Symptoms: Persistent condensation, mould, odours

Solution: Measure actual airflow with anemometer, upgrade fan if below Part F minimums

Prevention: Calculate extract rates accurately, use duct sizes per manufacturer specs

Blocked Background Ventilation

Issue: Trickle vents painted shut or blocked

Symptoms: Stuffy rooms, insufficient air supply for combustion appliances

Solution: Clean and open all trickle vents, ensure 8,000mm² per habitable room

Prevention: Label vents clearly, educate occupants on importance

Excessive Duct Runs

Issue: Long or kinked ductwork reduces airflow

Symptoms: Low extraction despite correct fan specification

Solution: Minimize duct length (< 6m), use rigid duct, avoid 90° bends

Prevention: Design shortest duct routes, use 45° bends instead of 90°

Noisy MVHR Systems

Issue: Unit vibration or high air velocity in ducts

Symptoms: Exceeds 30 dB in bedrooms, occupant complaints

Solution: Install vibration mounts, reduce fan speed, use larger diameter ducts

Prevention: Locate MVHR unit away from bedrooms, specify low-noise models

Ventilation System Costs 2026

Ventilation system costs vary significantly by system type, dwelling size, and installation complexity. Professional installation ensures Building Regulations compliance and optimal performance.

System Type	Equipment Cost	Installation Cost	Total (3-bed house)
System 1 - Intermittent Fans	£200-500	£300-700	£500-1,200
System 3 - MEV	£800-1,500	£700-1,500	£1,500-3,000
System 4 - MVHR	£2,000-4,000	£1,500-3,000	£3,500-7,000
PIV System	£400-800	£200-700	£600-1,500
Commissioning/Testing	-	£200-500	£200-500 (all systems)

System 1 - Intermittent Fans

Equipment £200-500

Installation £300-700

Total £500-1,200

System 3 - MEV

Equipment £800-1,500

Installation £700-1,500

Total £1,500-3,000

System 4 - MVHR

Equipment £2,000-4,000

Installation £1,500-3,000

Total £3,500-7,000

Part F Ventilation FAQs

What is Part F and why is it important?

Part F (Ventilation) of the Building Regulations ensures all buildings have adequate ventilation to maintain indoor air quality, remove moisture, dilute pollutants, and prevent condensation and mould growth. Updated in 2022, Part F sets minimum extract rates, background ventilation, and whole dwelling ventilation requirements. Compliance is mandatory for all new builds, extensions, and material alterations requiring Building Control approval.

What ventilation rate do I need for a kitchen?

Kitchens require either 30 l/s intermittent extract (adjacent to hob, with 30-minute overrun) OR 13 l/s continuous extract. Intermittent fans are typically activated by light switch with overrun timer. Continuous systems (MEV/MVHR) provide constant low-level extraction with boost function. Background ventilation of 4,000mm² is also required when using intermittent extract strategy.

Do I need trickle vents if I have mechanical extract?

Yes, if using System 1 (intermittent extract) or System 3 (continuous MEV), you need background ventilation through trickle vents: 8,000mm² per habitable room (living rooms, bedrooms) and 4,000mm² for kitchens. System 4 (MVHR) does NOT require trickle vents as it provides mechanical supply air directly. Blocking trickle vents reduces ventilation effectiveness and can cause Building Control failure.

What is whole dwelling ventilation and how do I calculate it?

Whole dwelling ventilation is the continuous fresh air supply for the entire dwelling, calculated as the greater of: (A) 0.3 l/s per m² of floor area, OR (B) bedroom-based rate (1-bed=13 l/s, 2-bed=17 l/s, 3-bed=21 l/s, 4-bed=25 l/s, 5-bed=29 l/s). Example: 100m² 3-bed house needs 30 l/s (100×0.3) vs 21 l/s (3-bed rate) = use 30 l/s. This applies to continuous systems (MEV/MVHR).

Can I install ventilation myself or do I need a professional?

Simple intermittent extract fans (System 1) can be DIY-installed if you're competent with electrical work (must comply with Part P Electrical Safety). However, MEV and MVHR systems require professional installation due to ductwork design, commissioning requirements, and airflow balancing. ALL systems require Building Control notification and commissioning certificates showing measured airflow rates meet Part F requirements before sign-off.

What is the difference between MEV and MVHR?

MEV (Mechanical Extract Ventilation) extracts stale air from wet rooms continuously, with fresh air supplied passively through trickle vents. MVHR (Mechanical Ventilation with Heat Recovery) is a balanced system that mechanically supplies AND extracts air, recovering 85-95% of heat from extracted air. MVHR is more expensive (£3,500-7,000) but more energy-efficient than MEV (£1,500-3,000). MVHR works best in airtight, well-insulated homes.

How often should ventilation systems be serviced?

Intermittent extract fans: Annual check, clean grilles every 3 months. MEV systems: Filter cleaning/replacement every 3-6 months, professional service annually. MVHR systems: Filter replacement every 3-6 months (critical), heat exchanger cleaning annually, full professional service every 2 years. Blocked filters dramatically reduce performance and increase energy consumption. Manufacturer instructions specify exact maintenance schedules.

What happens if my ventilation doesn't meet Part F?

Non-compliant ventilation results in: Building Control refusal to issue completion certificate, inability to sell property without retrospective compliance work, condensation/mould/damp issues requiring expensive remediation, poor indoor air quality affecting health, potential insurance claims for moisture damage. Commissioning testing identifies failures before final inspection - typical issues include undersized fans, blocked ducts, missing trickle vents.

Do I need purge ventilation in every room?

Purge ventilation (rapid air exchange via opening windows) is required in all habitable rooms (living rooms, bedrooms, kitchens) at 1/20th of floor area. A 20m² bedroom needs 1.0m² openable window area. NOT required in: internal bathrooms/toilets (extract sufficient), hallways, stairs, cupboards. Purge ventilation removes high pollutant concentrations and provides rapid cooling. Roof windows and opening doors can contribute to purge ventilation area.

What is Specific Fan Power (SFP) and why does it matter?

SFP (Specific Fan Power) measures electrical efficiency: fan power (Watts) ÷ airflow (l/s). Part F limits: intermittent fans ≤0.5 W/(l/s), MEV ≤0.4 W/(l/s), MVHR ≤1.5 W/(l/s). High SFP systems consume excessive electricity, increasing running costs and worsening SAP/SBEM energy ratings. Example: 20W fan delivering 30 l/s = 0.67 W/(l/s) fails Part F for intermittent use. Always check manufacturer SFP data before purchasing fans.