What is the difference between G4 and F7 filters?

G4 is a coarse filter that stops dust and larger particles; F7 is a fine filter that captures most pollen and fine particles. G4 typically protects the unit on the extract side, while F7 cleans the incoming supply air.

What happens if I do not change the filters?

A clogged filter restricts airflow, so the fans work harder and use more electricity, the home is under-ventilated, and the air quality the filter was protecting gets worse. It is a false economy.

How much do MVHR filters cost?

A replacement set typically costs about £20 to £125, depending on the brand, grade and unit. Over a year, with one or two changes, it is a modest ongoing cost.

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MVHR filters, explained

MVHR units use graded filters to clean the incoming air and protect the unit. The common grades are G4, M5 and F7, each capturing progressively finer particles. Choosing the right grade and changing filters on schedule keeps the air clean and the system working properly. This guide explains the grades and the maintenance.

By VentRight Editorial · Last updated 2026-07-08 · Impartial · Sourced

MVHR filter grades. Labelled: G4, M5, F7. — MVHR filter grades — labels

G4G4 — A coarse filter that stops dust and insects. Often used on the extract side to protect the unit.

M5M5 — A medium filter that catches finer dust and some pollen.

F7F7 — A fine filter that captures most pollen and fine particles. Often used on the fresh-air supply.

What do G4, M5 and F7 filters mean?

These are filter grades that describe how fine a particle each captures. G4 is a coarse filter that stops dust, insects and larger particles. M5 is medium, catching finer dust and some pollen. F7 is a fine filter that captures most pollen and fine particles, and is the grade usually specified where air quality matters, including for Passivhaus.

G4, M5 and F7 come from the older European filter classification. A newer standard, ISO 16890, rates filters by the particle sizes they capture, such as ePM1 and ePM10, and some current units quote these instead. The principle is the same: a higher grade captures finer particles. If you see an ISO rating, an F7 broadly corresponds to a filter that captures a good share of the finest particles.

Which MVHR filter grade should I use?

Most homes use a G4 filter on the extract side, to protect the unit, and an F7 filter on the supply side, to clean the incoming air. F7 is worth having in areas with poorer outdoor air or for anyone with allergies, as it captures fine particles and most pollen. Check what grades your unit takes, as this varies by model.

The supply filter is the one that affects the air you breathe, so that is where the finer F7 grade earns its place. The extract filter mainly protects the heat exchanger and fans from dust, so a coarser G4 is usually fine there. Fitting a finer filter than the unit is designed for can restrict airflow, so stick to what the manufacturer specifies.

How often should MVHR filters be changed?

As a general rule, filters are changed every 6 to 12 months, and more often, roughly every 3 to 6 months, for higher-grade filters or in areas with poor outdoor air. Follow the manufacturer schedule. A clogged filter restricts airflow, makes the fans work harder and pushes up running cost, so changing them on time matters.

Some units have a filter-change indicator; otherwise, set a reminder. Homes near busy roads or in dusty environments get through filters faster. Skipping changes is a false economy: the system moves less air, the fans use more electricity, and the air quality the filter was there to protect gets worse.

Why do MVHR filters matter?

Filters do two jobs: they keep the incoming air clean, and they protect the heat exchanger and fans from dust. A good filter, especially the finer F7 grade, improves indoor air quality. But filters only work if they are replaced on schedule; a neglected filter both worsens air quality and drags down the system performance.

A well filtered MVHR system is one of the quiet advantages of the technology: the fresh air arriving in the home has been cleaned of much of the pollen and fine particles from outside. That benefit disappears if the filters are left in past their life, when they clog and restrict the very airflow they are meant to clean.

How much do replacement MVHR filters cost?

Replacement filter sets typically cost somewhere between about £20 and £125 a set, depending on the brand, the grade and the unit. Over a year, with one or two changes, that is a modest running cost. Genuine manufacturer filters cost more than compatible ones, but a poor fit can let unfiltered air past, so fit matters.

Filter cost is a small but real part of the ongoing cost of MVHR, alongside the electricity to run the fans. Our running cost guide covers the electricity side. When comparing units, it is worth checking not just the filter grade but what replacement sets cost and how often they are needed.

Questions

What is the difference between G4 and F7 filters?: G4 is a coarse filter that stops dust and larger particles; F7 is a fine filter that captures most pollen and fine particles. G4 typically protects the unit on the extract side, while F7 cleans the incoming supply air.
How often do I change MVHR filters?: Usually every 6 to 12 months, and every 3 to 6 months for finer filters or in areas with poor outdoor air. Follow the manufacturer schedule, and change them sooner if a filter-change indicator prompts you.
What happens if I do not change the filters?: A clogged filter restricts airflow, so the fans work harder and use more electricity, the home is under-ventilated, and the air quality the filter was protecting gets worse. It is a false economy.
How much do MVHR filters cost?: A replacement set typically costs about £20 to £125, depending on the brand, grade and unit. Over a year, with one or two changes, it is a modest ongoing cost.