Why Ventilation Matters After Insulation
An uninsulated Irish home has plenty of natural ventilation through gaps in walls, around windows, through chimneys, and via the attic. When you insulate and draught-proof, you seal these gaps. That's great for keeping heat in, but it also traps moisture from cooking, showering, breathing, and drying clothes.
Without controlled ventilation, moisture builds up and causes condensation on windows, mould growth on walls and ceilings, musty smells, and poor indoor air quality. These problems often appear within months of insulating.
Types of Ventilation
MVHR (Mechanical Ventilation with Heat Recovery)
The gold standard for retrofitted homes. An MVHR system extracts stale air from wet rooms (kitchen, bathroom, utility) and supplies fresh filtered air to living rooms and bedrooms. A heat exchanger recovers up to 90% of the heat from the outgoing air, so fresh air comes in pre-warmed.
Cost: €3,500–6,000 fully installed. Requires ducting throughout the house, so it's easiest to install during a full retrofit when floors and ceilings are already being worked on.
Demand-Controlled Ventilation (DCV)
Individual extract fans in wet rooms that adjust speed based on humidity levels. Simpler and cheaper than MVHR but doesn't recover heat. Better suited to partial retrofits where full ducting isn't practical.
Cost: €1,500–3,000 for a whole-house system of demand-controlled extracts plus trickle vents in bedrooms and living rooms.
Positive Input Ventilation (PIV)
A single unit (usually in the attic) that pushes filtered air into the house, creating slight positive pressure that pushes stale air out through natural leakage points. The simplest retrofit option.
Cost: €800–1,500 installed. Less effective than MVHR but much cheaper and easier to install.
Which System Do I Need?
| Scenario | Recommended Ventilation |
|---|---|
| Full deep retrofit (BER B2 target) | MVHR (usually required for airtightness compliance) |
| Attic + wall insulation only | Demand-controlled ventilation or PIV |
| Attic insulation only | Ensure existing vents are unblocked, consider trickle vents |
| Adding a heat pump | MVHR recommended (heat pump works best in airtight homes) |
A BER is the starting point for most energy upgrades and grant applications. Homerating.ie has been assessing Irish homes since 2009, with fast turnaround in Dublin and nationwide coverage. Book a BER with Homerating.ie →
Frequently Asked Questions
Attic insulation alone doesn't usually require mechanical ventilation. But if you also draught-proof doors, windows, and add wall insulation, you're significantly reducing air exchange and should address ventilation.
Modern MVHR systems are very quiet, typically 25–35 dB in living spaces. That's quieter than a whisper. Ensure the unit is installed in a utility room or attic, not directly above a bedroom.
Ventilation is covered as part of a One Stop Shop retrofit package. There is no standalone SEAI grant for ventilation alone, but it's included in the overall grant when you do a full deep retrofit.