How do I size an MVHR unit for a dwelling?

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

What SFP should I target for Part L compliance?

Part L limits specific fan power for MVHR. Check the certified Eurovent data sheet at design duty — good practice targets ≤0.8 W/(l/s).

How does MVHR duct sizing relate to unit flow?

Main ducts are sized for continuous duty; branch ducts for extract boost. Use the duct sizing calculator for velocity and pressure-drop checks.

BuildFlo Design Guide · Ventilation · Approved Document F / AM13

MVHR sizing calculator for dwellings

Size mechanical ventilation with heat recovery — supply and extract flow rates under Part F. Free UK MVHR sizing calculator.

What this calculator does

MVHR sizing helps UK building services engineers with part f continuous mvhr duty, wet-room boost, heat recovery winter supply, and indicative ducts. The calculation follows Approved Document F / AM13 methods used in everyday MEP design — enter your project inputs below for a first-pass result.

Whether you searched for "mvhr sizing", "mvhr sizing calculator", or "how to mvhr size", this page gives you a working tool plus the context to use it on a real job.

When to use it

Use this for early-stage sizing and sanity checks on UK building services work. It is not a substitute for issued calculations — verify against the project specification, drawings, and relevant standard before sign-off.

How to use it

1. Fill in the inputs for your scenario (defaults are starting points only). 2. Click Calculate — results include the method and assumptions where applicable. 3. Verify against the project specification and relevant standard before issuing.

Typical output unit: l/s.

Tips

Defaults are indicative — replace with project-specific values from the architect, structural, or MEP spec.
For issued calculations, save results in your BuildFlo project and attach to the calculation folder.
Need the regulation citation? Open BuildFlo chat in the app and ask about mvhr sizing under UK standards.

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Frequently asked questions

How do I size an MVHR unit for a dwelling?: Size on the higher of AD F Table 1.2 (by bedrooms) and 0.3 l/s per m² floor area. Allow for boost on kitchen and bathroom extract branches.
What SFP should I target for Part L compliance?: Part L limits specific fan power for MVHR. Check the certified Eurovent data sheet at design duty — good practice targets ≤0.8 W/(l/s).
How does MVHR duct sizing relate to unit flow?: Main ducts are sized for continuous duty; branch ducts for extract boost. Use the duct sizing calculator for velocity and pressure-drop checks.