What's the difference between MVHR and ERV?

MVHR (Mechanical Ventilation with Heat Recovery) typically refers to a centralised whole-house system with ductwork. ERV (Energy Recovery Ventilator) can be either centralised or decentralised, but the term is often used for single-room units. The key technical difference is that ERVs recover both heat and moisture, while basic HRVs recover heat only. In practice, most modern systems — both centralised and decentralised — offer energy recovery.

Can I install a single-room ERV in an existing home?

Yes — that's their main advantage. A single-room ERV like Optim Vent installs through a single core hole in an external wall. No ductwork, no attic work, no ceiling voids. Most rooms are done in under two hours. It's the most practical option for retrofitting ventilation into existing Irish homes.

How many single-room ERV units do I need for my house?

Each unit covers up to 500 square feet. A typical 3-bedroom semi-detached house needs 2-3 units, usually in bedrooms where condensation and air quality are worst. You don't need to do every room — start with the problem areas and add more if needed.

Is whole-house MVHR better than single-room ERV?

Neither is universally better — it depends on your home. Whole-house MVHR is ideal for new builds where ductwork can be designed in from the start. Single-room ERVs are better for existing homes, renovations, and situations where running ductwork would be impractical or too expensive. Both achieve the same outcome: fresh, filtered air with heat recovery.

How much does whole-house MVHR cost vs. single-room ERV?

Whole-house MVHR typically costs €5,000-€10,000+ installed (including ductwork, the central unit, and making good). Single-room ERV units cost significantly less per unit, and you only install them where they're needed. For an existing 3-bed semi needing 2-3 rooms ventilated, single-room ERV is usually the more cost-effective option.

Single-Room ERV vs. Whole-House MVHR: Which Is Right for Your Home?

So you’ve decided you need heat recovery ventilation. Good call. But now you’re facing a choice: do you go with a whole-house MVHR system (one big unit in the attic, ducts to every room), or individual single-room ERV units (one per room, no ductwork)?

Both approaches work. Both provide fresh, filtered air with heat recovery. But they suit very different situations — and the wrong choice can cost you thousands in unnecessary installation, or leave you with a system that doesn’t perform as well as it should.

This guide gives you an honest comparison so you can make the right call for your home.

The Quick Version

Choose whole-house MVHR if: You’re building a new home or doing a major renovation where walls and ceilings are already being opened up. You want a single, invisible system with centralised control and maintenance.

Choose single-room ERV if: You live in an existing home and want to add ventilation without major disruption. You want to target specific problem rooms. You want a lower upfront cost with the option to expand later.

The reality for most Irish homeowners: If you’re reading this, you probably live in an existing house that already has condensation and mould problems. In that case, single-room ERV is almost always the more practical and cost-effective option.

How Each System Works

Whole-House MVHR

A centralised system. One unit (typically in the attic, utility room, or hot press) connected to the entire house via a network of insulated ducts.

The setup:

A central MVHR unit containing the heat exchanger, fans, and filters
Supply ducts running to bedrooms and living areas (delivering fresh air)
Extract ducts running from kitchens, bathrooms, and utility rooms (removing stale air)
Ductwork is typically run through the attic, ceiling void, or boxed in along walls
A single control panel or app manages the whole system

How it ventilates: Fresh air is pulled in from outside, filtered, and warmed by the heat exchanger using the warmth from the extracted stale air. The fresh air is distributed to “dry” rooms (bedrooms, living rooms) while stale air is extracted from “wet” rooms (kitchen, bathroom). This creates an airflow pattern through the house from supply rooms to extract rooms.

Single-Room ERV

A decentralised system. Individual units in each room that needs ventilation, each independently handling its own heat recovery.

The setup:

One compact unit per room, mounted on an external wall
Installed through a single core hole (150-160mm diameter)
Each unit contains its own ceramic heat exchanger, fan, and F7 filter
Units operate independently but can be coordinated via app
No ductwork, no attic unit, no ceiling work

How it ventilates: Each unit alternates between extracting stale air and supplying fresh air through its ceramic heat exchanger. During the extract phase, warm room air heats up the ceramic core. During the supply phase, cold outside air passes through the warmed ceramic, picking up the stored heat. This cycle repeats every 70 seconds or so, continuously ventilating the room with minimal heat loss.

The Honest Comparison

Let’s compare these two approaches across every factor that matters:

Installation

Factor	Whole-House MVHR	Single-Room ERV
New build	Straightforward — ducts designed into the build	Also straightforward, but overkill if you can do MVHR
Existing home	Very disruptive — ceiling voids, boxing, redecoration	Minimal — one core hole per room, 2 hours per room
Renovation	Good if walls/ceilings are already open	Good for targeted rooms or partial renovation
Listed/protected building	Difficult — internal ductwork may not be permitted	Easier — minimal internal impact
Apartment/flat	Usually impossible (no attic, shared ceilings)	Ideal — just needs an external wall

The verdict: For existing Irish homes, single-room ERV wins decisively on installation practicality. Running ductwork through a house that’s already finished — with furniture, decoration, and people living in it — is a major undertaking.

Cost

Factor	Whole-House MVHR	Single-Room ERV
Equipment	€2,000-€4,000 for the central unit	Lower cost per unit
Installation	€3,000-€6,000+ (ductwork, fitting, making good)	A couple of hours per room, minimal making good
Total for a 3-bed semi	€5,000-€10,000+	Significantly less for 2-3 rooms
Running cost	€30-€80/year (larger fans, longer duct runs)	~€10/year per unit
Maintenance	Annual filter changes + duct cleaning every 5-7 years	Filter changes every 6-12 months per unit

The verdict: Single-room ERV has a much lower upfront cost, especially in existing homes where the ductwork installation is the major expense. Running costs are comparable or lower for ERVs because the units are low-power (7.8W each) and there’s no duct resistance to overcome.

Performance

Factor	Whole-House MVHR	Single-Room ERV
Heat recovery efficiency	85-95% (typical installed performance)	Up to 97% (ceramic regenerator)
Air distribution	Even distribution to all rooms via ducts	Each room independently controlled
Filtration	Centralised F7 or higher	F7 per unit
Humidity management	Some units offer ERV mode	Built-in — ERV by design
Noise	Very quiet in rooms (fan is in attic), but ducts can transmit noise	Under 33dB at the unit
Failure mode	If central unit fails, entire house loses ventilation	If one unit fails, other rooms continue

The verdict: Performance is comparable. Whole-house MVHR can achieve slightly more even distribution, but single-room ERV often achieves higher heat recovery rates because there’s no duct heat loss. The redundancy advantage of decentralised systems (one unit failing doesn’t affect others) is genuinely useful.

Controllability

Factor	Whole-House MVHR	Single-Room ERV
Room-by-room control	Limited — central system serves all rooms equally	Full — each unit is independent
Boost mode	Whole-house boost (e.g., cooking mode)	Room-specific boost
Night mode	Whole-house reduced speed	Bedroom units can be set individually
Sensors	Central or zoned sensors	Per-room humidity and CO2 sensors
Schedules	Whole-house schedules	Per-room schedules

The verdict: Single-room ERV offers superior room-level control. You can run the bedroom unit on a quiet night mode while boosting the kitchen unit during cooking — something a whole-house system can’t do without expensive zone dampers.

Aesthetics

Factor	Whole-House MVHR	Single-Room ERV
Visibility	Invisible (ducts in ceiling void, grilles flush-mounted)	Unit visible on wall (compact, modern design)
Ceiling impact	May need lowered ceiling or boxing in some rooms	No ceiling impact
External appearance	One or two external vents	One small vent per room on external wall

The verdict: Whole-house MVHR is more invisible once installed — but the installation process is far more invasive. Single-room ERV units are visible but compact (Optim Vent is designed to be unobtrusive on the wall).

Which Is Right for Your Situation?

Choose whole-house MVHR if:

You’re building a new house and can design the ductwork in from the start
You’re doing a deep renovation where walls and ceilings are already stripped back
Every room needs ventilation and you want a single, centralised system
You prefer completely invisible systems and don’t mind the installation complexity
Your budget allows €5,000-€10,000+ and the disruption of ductwork installation

Choose single-room ERV if:

You live in an existing home and don’t want weeks of disruption
You have a specific problem — condensation in bedrooms, mould in the bathroom, stuffy living room
You want to start with one room and add more later based on results
Your home can’t accommodate ductwork — no accessible ceiling void, solid floors, or protected building
You want lower upfront cost with the flexibility to expand
You rent your property or you’re a landlord upgrading rental accommodation
You’re in an apartment or a home without attic access

The hybrid approach

Some homeowners use both: whole-house MVHR for the main living areas (installed during a renovation) and single-room ERV units for rooms that are difficult to reach with ductwork — or rooms added later (extensions, converted garages, attic conversions).

The Retrofit Reality in Ireland

Let’s be honest about the state of most Irish housing stock.

Ireland has roughly 2 million homes. The majority were built before modern ventilation standards existed. They have solid ceilings, no ceiling voids suitable for ductwork, and tight attic spaces. Many are semi-detached or terraced with limited access routes for ducting.

For these homes — which represent the vast majority of the market — whole-house MVHR is either impractical, prohibitively expensive, or both. The installation would require:

Creating ceiling voids or boxing ducts along walls in every room
Running ducts from the attic to ground-floor rooms (through walls or creating vertical runs)
Potentially lowering ceilings in some rooms
Significant making-good, replastering, and repainting
Weeks of disruption while you’re living in the house

Single-room ERV sidesteps all of this. One hole in the external wall per room. A couple of hours per room. Minimal making good. You can use the room that evening.

Common Questions

Can I mix single-room ERV units in some rooms with natural ventilation in others? Yes. Install ERV units in the rooms where you need them most (usually bedrooms and living rooms), and rely on extractor fans or trickle vents for rooms where moisture is less of an issue. You can always add more units later.

Do single-room ERV units “talk” to each other? Optim Vent units can be managed together through the app, so you can monitor and control all your units in one place. They don’t need to physically communicate with each other — each unit is independent.

What about Building Regulations Part F? Both whole-house MVHR and single-room ERV systems can meet Part F requirements for background ventilation. Your system should be designed to provide adequate ventilation for the room size and use — which your installer will calculate.

I’m getting external wall insulation — should I do ventilation at the same time? Absolutely. External wall insulation makes your home more airtight, which makes ventilation more important. Installing ERV units at the same time means the core holes are drilled before the insulation goes on, and the units are set at the correct depth for the new wall build-up. It’s also a great time to bundle it into an SEAI grant application.

What happens in a power cut? Both systems stop when the power goes out. For a single-room ERV, the auto-shutter closes to prevent draughts. When power returns, the unit resumes automatically. Whole-house MVHR is the same, though the ductwork may allow some natural draught through the system while it’s off.

Making Your Decision

Here’s a simple decision tree:

Are you building a new home? → Strongly consider whole-house MVHR. Design the ductwork into the plans from the start. It’s far easier and cheaper than retrofitting later.

Are you doing a major renovation with walls/ceilings already being opened? → Consider whole-house MVHR if the budget and building layout allow. Otherwise, single-room ERV is still the practical choice.

Are you living in an existing home with condensation, mould, or air quality issues? → Single-room ERV. Start with the worst-affected rooms. Optim Vent installs in a couple of hours per room with minimal disruption.

Are you in an apartment, a listed building, or a home without suitable attic space? → Single-room ERV is your only practical option — and it works brilliantly.

Not sure? → Get in touch for a free home assessment. We’ll look at your home and recommend the right approach.