Passivhaus ventilation

Does a Passivhaus need MVHR?

In practice, yes. A Passivhaus is built to an extreme airtightness of 0.6 air changes per hour at 50 pascals, far tighter than Building Regulations require, so natural ventilation cannot supply enough fresh air. MVHR with high heat recovery is the standard way to ventilate a Passivhaus without losing the heat the airtightness is designed to keep in.

The whole Passivhaus approach depends on keeping heat in, so ventilating with uncontrolled leakage or open windows would undo it. MVHR provides constant filtered fresh air and recovers most of the warmth from the air it extracts, which is exactly what an ultra-airtight, ultra-insulated home needs. That is why MVHR and Passivhaus are so closely associated.

What airtightness does Passivhaus require?

Passivhaus requires an airtightness of no more than 0.6 air changes per hour at 50 pascals, measured by a pressure test. This is much tighter than the UK Building Regulations air permeability limit and is one of the reasons MVHR is needed: at that airtightness, a home has almost no uncontrolled airflow to bring in fresh air.

The Passivhaus figure is quoted in air changes per hour, while UK Building Regulations use air permeability in cubic metres per hour per square metre. They measure the same thing in different units, but the Passivhaus target is far more demanding. Meeting it is what makes controlled mechanical ventilation essential rather than optional.

What does Passivhaus certification of an MVHR unit mean?

A Passivhaus-certified MVHR unit has been independently tested against the Passivhaus Institut criteria for heat recovery efficiency, fan power, airtightness and comfort, and listed in the PHI component database. Certification gives confidence that the unit performs as claimed under a consistent, demanding test, which is why Passivhaus projects specify from that list.

Certification is not just a badge. It sets minimum performance levels and verifies them independently, so a certified unit is a known quantity. For a certified Passivhaus building, using certified components is part of how the whole result is guaranteed, but the same units are also a safe choice for any high-performance home.

Sources: Passivhaus Institut

Where do I find certified Passivhaus MVHR units?

The Passivhaus Institut component database lists all certified ventilation units, with their tested heat recovery efficiency, specific fan power and other figures. It is the reference designers use to choose a unit for a certified project, and a useful neutral source for anyone comparing high-performance units, whether or not they are building to Passivhaus.

Because the database uses one consistent test method, it lets you compare units on equal terms, which manufacturer datasheets do not always allow. Even outside a formal Passivhaus project, it is one of the most reliable places to check a unit real performance before specifying it.

Sources: Passivhaus Institut

Can I build to Passivhaus standards without full certification?

Yes. Many homes are built to Passivhaus principles, sometimes called Passivhaus-inspired, without going through formal certification. They still benefit from high airtightness and MVHR. The difference is that certification independently verifies the result, whereas an inspired build relies on the design and construction being done well without that check.

Formal certification adds cost and process, so some self-builders aim for the performance without the paperwork. That can work well when the team is experienced, but it removes the independent check that a certified project gets. Either way, the ventilation logic is the same: an airtight home needs MVHR to stay fresh and warm.