What ventilation system type should I use in a new dwelling?

System 4 MVHR is common on new-build flats and efficient dwellings. System 3 MEV with trickle vents suits simpler schemes. Check AD F system descriptions.

How do I size MVHR for a flat?

Use the higher of AD F Table 1.2 (by bedrooms) and 0.3 l/s per m² floor area. Allow boost on kitchen and bathroom extract branches.

What acoustic limits apply to ventilation fans?

AD F Section 1.23 sets maximum sound levels for continuous ventilation. Select fans with published SFP and acoustic data at design duty.

BuildFlo Design Guide · Ventilation · Approved Document F

Dwelling ventilation design under Part F

Whole-dwelling and room extract rates under Approved Document F. MVHR, MEV and trickle vent guidance with built-in calculators.

Approved Document F 2021 Volume 1 sets minimum ventilation for new and materially altered dwellings in England. Wales and Scotland have aligned but not identical requirements - check the jurisdiction.

For MEP engineers on residential schemes, Part F drives whole-dwelling continuous rate, intermittent extract, and background ventilator provision.

Whole-dwelling continuous ventilation (Table 1.2)

AD F gives a rate by bedroom count, checked against 0.3 l/s per m² of internal floor area - use the higher value.

Bedrooms	Minimum continuous rate
1	13 l/s
2	17 l/s
3	21 l/s
4	25 l/s
5	29 l/s

Example: A 2-bed flat at 80 m² → Table gives 17 l/s; floor-area check gives 0.3 × 80 = 24 l/s → 24 l/s governs.

Intermittent extract (Table 1.1)

Room	Minimum extract
Kitchen ( adjacent to hob )	30 l/s ( or 60 l/s cooker hood )
Kitchen ( no hob adjacent )	15 l/s
Utility	15 l/s
Bathroom	15 l/s
Sanitary accommodation	6 l/s

Boost switches or automatic boost on kitchen/bathroom extract are required when using centralised continuous systems ( MVHR/MEV ).

System types - quick decision guide

System 1 - Background ventilators + intermittent extract - Trickle vents + bathroom/kitchen fans. Common on small refurbishments.
System 2 - Passive stack - Restricted; specialist design.
System 3 - Continuous MEV - Centralised or decentralised extract; make-up air via trickle vents.
System 4 - MVHR - Balanced supply/extract with heat recovery. Typical on new-build flats and Passivhaus-aligned schemes.

MVHR units are sized on the continuous duty. Ductwork is sized for that flow plus boost on extract branches.

Checklist before you issue

Whole-dwelling rate meets Table 1.2 and 0.3 l/s per m²
Kitchen and bathroom extract rates to Table 1.1
Trickle equivalents if not using MVHR throughout
Acoustic limits for fans ( AD F Section 1.23 )
Commissioning and user handover information scheduled

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*BuildFlo's ventilation calculator applies AD F Table 1.2 and the floor-area minimum automatically.*

Frequently asked questions

What ventilation system type should I use in a new dwelling?: System 4 MVHR is common on new-build flats and efficient dwellings. System 3 MEV with trickle vents suits simpler schemes. Check AD F system descriptions.
How do I size MVHR for a flat?: Use the higher of AD F Table 1.2 (by bedrooms) and 0.3 l/s per m² floor area. Allow boost on kitchen and bathroom extract branches.
What acoustic limits apply to ventilation fans?: AD F Section 1.23 sets maximum sound levels for continuous ventilation. Select fans with published SFP and acoustic data at design duty.