Which ventilation system do I need?

Which ventilation system does a new build or airtight home need?

A new build or any very airtight home usually needs MVHR, mechanical ventilation with heat recovery. At that airtightness there is too little natural airflow to keep the home fresh, and MVHR supplies filtered fresh air while recovering most of the heat that ventilation would otherwise lose. It is the standard choice for new builds and deep retrofits.

Building regulations require adequate ventilation, and in an airtight home a mechanical system is normally the only reliable way to provide it. MVHR is not the only compliant option, but it is the usual one where the home is airtight, because it avoids the heat loss of simpler systems.

Sources: GOV.UK

Which ventilation suits a reasonably airtight home?

A reasonably airtight home is often well served by continuous mechanical extract, either MEV with a central fan or dMEV with a fan in each wet room. These continuously remove stale air from kitchens and bathrooms while fresh air enters through background vents. They are simpler and cheaper than MVHR but do not recover heat.

Continuous extract is a good middle ground for homes that are tighter than an old draughty house but not built to new-build airtightness. If the home is or becomes very airtight, MVHR usually becomes the better choice so that the ventilation does not waste heat.

Which ventilation suits a leaky older home with condensation?

A leakier older home, particularly one with a condensation problem, can often be helped by positive input ventilation, PIV. A loft unit gently pushes filtered fresh air through the home, diluting damp, stale air and pushing it out through gaps. It is low cost and simple to fit, but it has no heat recovery, so it does not suit a very airtight home.

PIV works with the leakiness of an older home rather than against it, which is why it is a common damp and condensation fix. In a home that is being made airtight, or a new build, there is nowhere for the stale air to escape, so PIV is the wrong tool and MVHR or continuous extract is appropriate instead.

How does the ventilation selector work?

The selector asks about your build type, how airtight the home is, and whether there is a damp problem, then points to the system most likely to suit. It is a starting point, not a substitute for a ventilation design. The right choice also depends on layout, budget and, for a new build, your airtightness test result.

The logic follows the same rule most designers use: the more airtight the home, the more it needs mechanical ventilation, and heat recovery becomes worthwhile once the home is tight enough to hold the heat. Where the answers are unclear, the selector recommends a ventilation assessment rather than guessing.