How to compare MVHR units

What should I compare when choosing an MVHR unit?

Compare five things: heat recovery efficiency, how much heat the unit keeps; specific fan power, how much electricity it uses to move air; noise, in decibels; the filters it takes; and whether it is certified. Comparing units on these, using tested figures rather than marketing claims, tells you far more than a headline price or a single number.

Price matters, but a cheap unit with high fan power can cost more over its life because it runs continuously. Likewise a high efficiency unit that is noisy or takes expensive filters may not be the right pick. Weigh the five factors together against your home and budget rather than chasing any single best number.

What heat recovery efficiency and fan power should I look for?

Look for high heat recovery efficiency and low specific fan power together. As a benchmark, the Zehnder ComfoAir Q range quotes up to 96 percent heat recovery efficiency and a specific fan power as low as around 0.53, and is Passivhaus certified, which places it at the premium end. Economy units sit lower on both. Check the tested figures in the Passivhaus database rather than trusting a single quoted number.

Efficiency and fan power pull in the same direction on cost: a unit that recovers more heat and uses less electricity to do it is cheaper to own. The premium units lead on both, but many homes are well served by a solid mid-range unit. The point is to compare like with like, using tested data.

Sources: Zehnder Group UK

How much noise should an MVHR unit make?

A good MVHR unit is quiet in the living space. The Zehnder ComfoAir Q, for example, is quoted at around 42 decibels at the unit, where some units run closer to 50. What you actually hear in a room also depends heavily on the ducting and the installation, so even a quiet unit can be noisy if it is badly fitted.

Noise is one of the most common complaints about MVHR, and it usually traces back to design, undersized or crushed ducting, or a unit sited too close to a bedroom, rather than the unit itself. A quiet unit is a good start, but a proper duct design and installation matter just as much.

Sources: Zehnder Group UK

What filters do MVHR units use?

MVHR units use graded filters, commonly G4 for general dust and F7 for fine particles and pollen. The Zehnder ComfoAir Q takes G4 and F7, with F7 used for Passivhaus. Better filtration improves indoor air quality but the filters need changing on schedule. Check which grades a unit takes and what replacement filters cost before buying.

Filter cost is an ongoing expense that varies a lot between brands, so it is worth factoring in. An F7 filter captures much finer particles than a G4, which matters for allergies and in areas with poorer outdoor air. Whatever the grade, filters only work if they are replaced on time.

Sources: Zehnder Group UK

Where can I find neutral MVHR unit figures?

Two databases hold tested figures rather than marketing claims. The Passivhaus Institut component database lists certified units with their heat recovery efficiency and fan power, measured by one consistent method. The UK Product Characteristics Database, at ncm-pcdb.org.uk, lists units used in SAP energy calculations. Between them they let you compare units on equal terms.

Manufacturer datasheets are a useful starting point but can quote figures under favourable conditions. The databases put units on the same footing, which is exactly what you need when comparing across brands. Use them to sanity check any headline number before you rely on it.

Sources: Passivhaus Institut; BRE / DESNZ