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What Is Mechanical Extract Ventilation and What’s the Difference Between DCV Ventilation?
A mechanical extract ventilation – MEV – system keeps your home fresh and energy-efficient. In essence, it continuously removes stale, moist air from “wet” rooms while drawing filtered air into living spaces through background vents.
Moreover, demand control ventilation (DCV) adds smart sensors that automatically increase or reduce airflow depending on indoor air quality or occupancy. In practice, you can think of MEV as “DCV without smart sensors” — same function, just less automated.
Consequently, you enjoy cleaner indoor air, less condensation, and—when the system is properly designed, installed, and commissioned—an easier route to demonstrating compliance with TGD Part F (2019) and TGD Part L (2022) for Irish dwellings.
Why Mechanical Extract Ventilation Matter for Irish Homes
Cleaner Indoor Air
Continuous extraction removes moisture, CO₂, and odours from bathrooms, kitchens, and utilities. As a result, rooms stay fresher and healthier all day.
Condensation & Mould Protection
Because MEV ventilation runs constantly, it prevents damp and mould even in airtight new builds.
Energy-Smart Operation
Unlike traditional fans, MEV avoids uncontrolled draughts. Furthermore, DCV ventilation systems use intelligent sensors to increase airflow only when needed—cutting unnecessary energy loss.
How a Mechanical Extract Ventilation System Operates
Centralised vs Decentralised dmev ventilation
Centralised MEV (CMEV)
A single high-efficiency fan connects via ductwork to multiple rooms. It delivers steady airflow and operates quietly. Therefore, it suits most modern airtight homes.
Decentralised MEV (dMEV ventilation)
Alternatively, each wet room has its own low-energy fan. This approach is ideal for retrofits or smaller properties where full duct runs are impractical.
What Does DCV Stand For
Compared with standard Mechanical Extract Ventilation, Demand Control Ventilation system offer the same reliability but deliver greater long-term savings.
Benefits of MEV System
Compliance with Irish Building Regulations
Ventilation (TGD Part F 2019)
Mechanical or natural ventilation systems must deliver the minimum airflow rates specified in Section 1.2 of TGD Part F.
For natural ventilation, controllable background ventilators with a minimum equivalent area of 2,500 mm² must be installed in every habitable room (except wet rooms), as clarified in the 2019 correction note .
All fixed mechanical ventilation systems (MEV/MVHR) must be commissioned and airflow-tested in accordance with Section 1.2 and the Installation and Commissioning Guide , ensuring correct extract, supply and internal transfer (10 mm door undercuts).
Energy (TGD Part L 2022)
Part L requires limiting air infiltration “as far as practicable” and defines airtightness backstops for new dwellings.
Typical targets are ≤ 5 m³/h·m² at 50 Pa, and dwellings with improved airtightness must incorporate appropriate continuous mechanical ventilation systems to avoid condensation and ensure indoor air quality, in line with Section 0.2.3 of Part L .
Validation
All mechanical ventilation systems must be commissioned and documented.
Following commissioning, airflow rates may also require independent third-party validation (NSAI Ventilation Validation Registration Scheme, Rev 7), depending on the project’s Building Control / certification requirements.
Where required, validated flowrates form part of the ancillary certification for Building Control sign-off.
Our Mechanical Extract Ventilation Process
Assessment & Design
We visit your home, inspect the layout and identify duct routes.
We then:
– Calculate the required extract and whole-house flow rates in accordance with TGD Part F 2019 Section 1.2.2.
– Select the appropriate MEV or DCV strategy (centralised or decentralised).
– Size all ductwork, terminals and background ventilators to meet the required design airflow rates.
– Confirm positions of wet-room extracts, background ventilators (min. 2,500 mm² EA per room except wet rooms, as per corrections to Part F) .
– Provide a layout drawing and builder-coordination notes for first fix.Installation
Our engineer carry out the installation following the Installation & Commissioning Guide Part F 2019 (Sections 2 & 3) .
Then:
– Install the MEV/DCV unit in the agreed location with compliant access for servicing.
– Fit supply/extract terminals and run all ductwork using rigid or semi-rigid systems sized to reduce resistance and noise.
– Ensure all duct joints are sealed and supported to prevent leakage.
Provide transfer paths under internal doors (min. 10 mm undercut as required by TGD F 1.2.1.2) .
Coordinate with builders for air-tightness works, ceiling closures and penetrations.
Typical installation duration:
Centralised MEV / DCV: 1–2 days
Decentralised MEV (dMEV): Often completed same dayCommission & Balance
We commission the system as required under TGD F, EN 14134, and NSAI D-IAB-009.
During commissioning we:– measure extract rates in every wet room using calibrated equipment
balance the system so total extract matches the design requirement
– verify boost modes, sensors (humidity/CO₂), timers and user controls
– record all airflow readings on the official Part F commissioning sheetsIndependent Validation (Where Required)
Where independent validation is required, an NSAI-certified validator independently verifies the system performance and documentation.
The validator typically:
– measures and records the final airflow rates at the terminals / key test points
– verifies that installation, balancing and commissioning documentation align with TGD Part F 2019, Clause 1.2.1.10 (as applicable to the dwelling/system type)
– confirms that the measured performance is consistent with the system’s design intent to support moisture control and indoor air quality (IAQ), provided the system is operated as intended
– issues a formal ventilation validation certificate, which may be used as supporting evidence for Building Control sign-off and (where accepted/required) for BER-related documentationHandover Documentation
We complete the project by providing:
– the commissioning report with measured flowrates
– user manual and operating instructions
Supply:
- Full MEV / DCV system (centralised or decentralised)
- Commissioning sheets & documentation (Part F compliant)
Tools:
- Bosch D-Tect 200
- Bosch laser distance measurer (with slope meter)
- Endoscope camera
- Drill + holesaw set
- Dust extractor with attachments
- DeWalt multitool
- Core drill (diamond)
- Ladder
- Multimeter
- Tape measure
- Screwdrivers & bits
- Tin snips
- Angle grinder
- Silicone gun
- PPE: mask, gloves, goggles
Materials: Ductwork – rigid or semi-rigid ( PVC / metal) Duct insulation Air valves (extract) Room terminals / grilles External wall/roof terminals (weatherproof cowls or hoods) Controllers / boost switches / humidity or CO₂ sensors Fire-rated duct components Mounting brackets & anti-vibration mounts All duct seals & gaskets (EPDM / rubber) Manifolds Attic walk-board / 1.5 m² platform if needed Fixings: screws, strap banding, anchors, supports Electrical connection materials (isolation switch, cable)
Notice
If a system was not designed or installed by Eco Vent, we can still commission and report on it. However, design or installation faults remain the responsibility of the original contractor.
Is MEV / DCV Ventilation Right for Your Property?
Choose MEV/DCV when:
Choose MVHR when:
- You want efficient, low-maintenance ventilation
- Space or budget limits MVHR installation
- You’re retrofitting or upgrading an airtight dwelling
- You require both heat recovery and maximum energy savings
- Full supply and extract ductwork is workable
Typical Applications
- New-build homes and apartments
- Retrofits and extensions
- Rental or student housing
- Low-energy and NZEB dwellings
Costs & Long-Term Value
MEV and DCV systems represent a cost-effective way to protect your property and reduce energy bills. Because airflow adjusts automatically, fan energy and heat loss are kept to a minimum. Over time, this translates into lower running costs and better comfort—particularly under Part L 2022 airtightness standards.
Why Choose Eco Vent
FAQ
How much does an MEV system cost?
An MEV system typically ranges from €1,500 to €3,000, which includes the design, supply, installation, and commissioning.
How much does a DCV system cost?
A DCV system usually costs between €2,000 and €3,500, covering full design, supply, installation, and commissioning.
What affects the final price?
Several factors influence the total project cost, including:
- whether the project is a new build or a retrofit
- overall floor area
- number of extract points required
- number and type of smart sensors (such as PIR boost sensors or additional humidity sensors)
What’s the difference between mechanical extract ventilation and a bathroom ventilation fan?
A standard bathroom fan is intermittent and serves only one room.
Mechanical Extract Ventilation (MEV), by contrast, operates continuously and serves all wet rooms in the home, providing consistent whole-house moisture control and stable indoor air quality.
Where should MEV systems be installed?
Typical extract locations include:
- kitchens
- bathrooms and shower rooms
- utility rooms
- WCs or sanitary accommodation
How loud are MEV/DCV systems?
When installed correctly, both MEV and DCV systems operate at very low noise levels. DCV units often run at reduced speeds for most of the day, which makes them even quieter during normal operation.
Do I still need a cooker hood with MEV?
Yes.
Part F requires a dedicated kitchen extract rate of 13 l/s, and the cooker hood is not counted toward this requirement. A separate boost extract must still be provided.
Is DCV worth the upgrade?
In many situations, yes.
DCV is particularly beneficial in airtight homes because it maintains comfort, adapts airflow automatically, and reduces running costs through demand-based operation.
Do I still need wall vents or window vents if I install MEV?
Yes — a fresh air pathway is still required.
Mechanical Extract Ventilation continuously removes stale and humid air, and Demand Controlled Ventilation removes it as needed, but neither system supplies fresh air into the home.
To maintain balanced airflow, the system relies on wall vents, trickle vents in windows, or dedicated air inlets—usually located in living rooms and bedrooms.
Get Compliant, Comfortable Ventilation Today
Breathe cleaner air and ensure full regulatory compliance with a custom-designed MEV/DCV system from Eco Vent.