Mechanical Ventilation with Heat Recovery: How It Works, What It Costs, and Why the Numbers Don't Agree
A mechanical ventilation with heat recovery system, usually shortened to MVHR, swaps the entire volume of air inside a home roughly every two hours, continuously, day and night, according to industry figures reported by BioBuilds (2026). No window needs to be opened — windows can still be opened as desired, but the system keeps air moving without them. No draught is felt. Yet the stale, moist air from the kitchen and bathrooms is pulled out, and fresh air comes back in, pre-warmed by the heat the house was about to lose anyway.
That part is not in dispute. What is in dispute, at least on paper, is how efficient the whole process actually is. Depending on which source a homeowner reads, MVHR units recover anywhere from 70% to 95% of that heat. Both numbers can be true at once, because they are not measuring the same thing. Understanding why is the difference between buying a system that performs as advertised and buying a brochure.
Key Takeaways
- Two separate air streams, one going out and one coming in, cross through a single heat exchanger without mixing, so the stale air warms the fresh air without the two ever touching.
- MVHR performs best in buildings that are already reasonably airtight — new builds or homes undergoing a full refurbishment, not a leaky older property with the odd upgrade.
- The percentage on a spec sheet is rarely the percentage a household actually gets; duct insulation, filter maintenance and balanced airflow decide the real-world result.
- A fully installed central system in Germany runs to roughly €8,900–15,600 according to 2026 figures from co2online, with planning, unit and installation each contributing a separate slice of that range.
- Because incoming air is already warm, heating costs can fall by 10–30%, according to UK guidance from the Centre for Sustainable Energy (CSE) — but the system itself generates no heat.
How Does MVHR Actually Move Air and Heat?
Inside the unit, two air streams run past each other through a single heat exchanger, close enough to transfer warmth but never close enough to mix, according to CSE. The outgoing stream is the air you want to get rid of: moist, stale, loaded with cooking smells. The incoming stream is outdoor air that would otherwise arrive cold. As they pass each other inside the exchanger, the outgoing air gives up its heat to the incoming air before either one continues on its way.
The routing follows the logic of how a home is actually used. Extraction happens where moisture and odours are generated — kitchen, bathrooms, utility room, WC — while the pre-warmed supply air is delivered to bedrooms and living rooms, according to Ecovent, an Irish ventilation specialist. The system also adapts to the seasons. A summer bypass setting routes cooler night air around the heat exchanger instead of through it, so the house can be cooled overnight without dragging in the following day's heat, according to BioBuilds (2026). A boost mode, triggered automatically or manually, briefly raises the fan speed during cooking or a shower, clearing moisture faster than the default setting would.
One clarification matters more than any spec number: MVHR is not a heater. It conserves heat that is already inside the building envelope; it does not generate any, according to BioBuilds (2026). A poorly insulated house with an MVHR unit is still a poorly insulated house — the ventilation system just stops that house from throwing away even more heat through open windows and extractor fans.
Central or Decentralised: Which Setup Fits Which Project?
A central MVHR system sits in one place — a cupboard, a utility room, or the loft — and distributes air through ducting concealed in ceiling cavities throughout the house, according to CSE. That ducting is also where things can quietly go wrong: if the unit sits in a cold loft, both the ducts and the condensate pipe need proper insulation, or the system loses efficiency before the air even reaches a room, CSE notes.
Decentralised MVHR works differently. Instead of one central unit and a network of ducts, paired fans sit on opposite walls of a room and exchange air directly through the wall, a layout CSE describes as cross-flow ventilation. Because there is no ducting to install, decentralised systems are generally the cheaper route.
That cost difference points to a sharper decision than brand or model. Retrofitting ducting into a finished house is difficult, because it demands space that often doesn't exist behind existing walls and ceilings, and because the whole approach depends on a level of airtightness the building may not have, according to CSE. MVHR, central or decentralised, performs best in buildings that are already fairly airtight — new builds, or homes mid-way through a full refurbishment, CSE notes. Reliable euro cost ranges for decentralised systems are scarce; where that gap exists, it is worth treating any single quoted figure with caution rather than assuming it represents the market.
Why Heat-Recovery Percentages Range from 70% to 95%
Line up the claims side by side and they look contradictory. CSE, in UK guidance, puts typical MVHR heat-recovery efficiency at 80–90%. Ecovent, writing for the Irish market, says a good unit keeps around 90% of the heat an ordinary extract fan would waste, and lists one specific model at 89–93%. German figures from co2online, reported in 2026, put modern residential units between 75% and over 90%, while noting that Passivhaus certification requires a minimum of 75%. BioBuilds (2026) cites Zehnder systems it installs as recovering around 95%. And Ireland's building regulations, Part L, set a minimum of 70% heat recovery for a unit fitted in a new home, according to Ecovent.
None of these numbers are wrong. They are answering different questions.
- A regulatory floor, such as Ireland's Part L 70% minimum, is the lowest a unit is legally permitted to achieve in a new home — a baseline, not a target.
- A tested, listed figure is what a specific unit actually measured under a standardised laboratory test (EN 13141-7) and entered into Ireland's product database, the PCDB, according to Ecovent — this is the number worth asking an installer to produce for the exact model being quoted.
- A certification threshold, like the Passivhaus Institute's 75% minimum referenced by co2online, is a design standard a building aims to meet, not a universal performance figure.
- A marketing claim, such as the roughly 95% BioBuilds attributes to Zehnder units, describes what a manufacturer states its product achieves under its own conditions.
What MVHR Costs: Reading Quotes Across Markets
Cost figures are just as scattered as efficiency figures, and for a similar reason: they come from different markets, in different currencies, describing different scopes of work. In the UK, CSE puts decentralised MVHR at £600 per fan upward, and puts central systems at around £3,000, potentially exceeding £10,000. In Germany, co2online's 2026 figures put a fully installed central system at roughly €8,900 to €15,600.
Neither figure should be read as a Belgian price. They are useful for a different reason: the German range breaks down into three components that apply logically wherever ducted MVHR is installed, even if the absolute euros differ locally.
- Planning: roughly €400–600 in the German figures, covering the design of the duct layout and airflow balancing.
- Unit and materials: roughly €6,000–9,000, covering the heat-exchanger unit itself, ducting, valves and controls.
- Installation: roughly €2,500–6,000, covering the physical work of routing ducts and fitting the unit.
The Real Running Cost: Filters, Cleaning, and Building Your Own Number
The installed price is only the first number. MVHR needs upkeep, and skipping it undoes much of what the system is bought for. Filter replacement costs roughly €50–100 a year, and a full professional clean of the unit and ducts, recommended every two to five years, runs €150–400, according to BioBuilds (2026). Changing a filter itself typically takes only minutes with a slide-out cassette, but a neglected one quietly degrades both airflow and filtration, the same source notes — the system keeps running, just worse.
Here is one way to turn those figures into a personal estimate, built only as an illustration and not as a quote for any specific project: say a household budgets €75 a year for filters and one professional clean every three years at €275. Over ten years, that's roughly €750 in filters plus three cleans at €275 each (around €825), landing around €1,575 in running costs across the decade — on top of, not instead of, the installation price discussed above.
The exact figures for any real household will differ by unit size, local service pricing and how the household actually uses the boost setting. The method, not the total, is what transfers: take a local installer's quoted filter and service intervals, multiply by the years the system is expected to run, and add that to the installed price before comparing two competing quotes.
Frequently Asked Questions
Can I still open windows with MVHR installed? Yes. MVHR is a continuous background system, not a seal on the building. Opening a window occasionally doesn't damage the unit; it simply bypasses it for as long as the window stays open, losing whatever heat the system would have recovered from that air.
Is MVHR a heating system on its own? No. It conserves heat already present in the air leaving the building; it does not produce heat, according to BioBuilds (2026). A home still needs its own heating system sized for its actual heat loss — MVHR reduces that heat loss; it does not replace the heating system. That reduction is why heating costs can fall by 10–30% once a system is fitted, according to UK guidance from CSE — the saving comes from avoided heat loss, not from the unit generating warmth itself.
How much electricity does the unit itself use? Running continuously, an MVHR unit draws roughly as much electricity as a light bulb, according to BioBuilds (2026). That low draw is part of why the heating savings tend to outweigh the running cost of the fans themselves, though the two are measured separately.
Can MVHR be added to an existing house, or only a new build? It can be added to an existing house, but the feasibility question comes before the cost question. Retrofitting means finding routes for ducting through a building that wasn't designed around it, according to CSE. Decentralised, ductless systems sidestep much of that problem, which is one reason they tend to suit constrained renovations better than central systems do.
Conclusion
The percentage on the brochure is the least useful number in this whole decision. The figure that matters is whether the ducting was planned before the walls closed, whether the loft run is insulated, and whether someone will actually change the filter on schedule. Those three things, not the gap between 80% and 95%, decide what a household gets back in practice.
Before signing a quote, it's worth asking the installer for the tested figure of the specific unit being proposed, not the general claim for the product line — and checking any imported percentage or price range against local building-performance standards, and confirming it with a certified local installer, rather than assuming a UK, Irish or German figure applies as read.
