Ventilation & MVHR: capacity, cost and efficiency

What commercial ventilation and MVHR are, and how they work

Ventilation is the deliberate supply of fresh outside air and extraction of stale air, and it is the single HVAC function that most directly shapes how a building feels to be in. Where an air handling unit is the big central lung, commercial ventilation is the wider strategy — the supply and extract fans, the heat-recovery units, the CO2 and occupancy sensing, and the ductwork that together control the air people actually breathe. Get it wrong and you have stuffy rooms, high CO2, poor concentration and complaints. Get it right and you have a healthy, alert building that costs surprisingly little to keep that way.

The technology that makes efficient ventilation possible is MVHR — mechanical ventilation with heat recovery. An MVHR unit brings in fresh air and extracts stale air through a single unit with a heat exchanger between the two streams. In winter, the warm outgoing air pre-heats the cold incoming fresh air; in summer the logic reverses. A good commercial MVHR unit recovers up to around 90 per cent of the heat in the exhaust air, which transforms the economics of ventilation. Without heat recovery, every cubic metre of fresh air you bring in for good air quality carries a heating or cooling cost. With it, you get the air quality and keep almost all of the energy.

Demand-controlled ventilation — supplying air only when it is needed

The second efficiency lever is demand-controlled ventilation (DCV). Rather than ventilating every space at full rate all the time, DCV uses CO2 sensors and occupancy detection to supply fresh air where and when it is actually needed. A meeting room full at 10am gets full ventilation; the same room empty at 3pm gets almost none. Because ventilation fan and conditioning energy runs whenever the system is on, matching the fresh-air rate to real occupancy saves both fan energy and the heating and cooling energy that would otherwise temper unnecessary air. MVHR handles the heat penalty of the air you do bring in; demand control minimises how much air that is. Together they are why modern commercial ventilation can deliver excellent indoor air quality without an energy penalty.

How ventilation differs from air handling — and where each fits

There is real overlap between this system type and air handling units, and it is worth being clear. A large central AHU is one way to ventilate a building; a network of smaller distributed MVHR units and demand-controlled supply/extract fans is another. Big central plant suits large, uniform spaces; distributed MVHR and DCV suit buildings with variable, cellular occupancy where you want to ventilate spaces independently. Many buildings use both — a central AHU for the main floor plate, local MVHR and demand control for meeting rooms, and dedicated extract for kitchens and toilets. The right strategy depends on the building’s layout and how its occupancy varies, which is why ventilation is designed as a system, not bought as a box.

Typical applications where a distributed, demand-controlled ventilation strategy shines:

• Offices — variable, cellular occupancy where DCV avoids ventilating empty rooms all day.
• Schools and public buildings — high-occupancy classrooms and halls where CO2 control is directly linked to concentration and where fresh-air rates are scrutinised.
• Leisure — high-fresh-air, high-humidity spaces where ventilation controls comfort and condensation.
• Mixed-use — buildings combining uses with very different ventilation needs on different floors.

Ventilation by building type — why one strategy never fits all

The ventilation duty changes sharply with the building, and that is what makes ventilation a design problem rather than a product purchase. In a school, CO2 is the headline: a classroom of thirty pupils pushes CO2 up fast, and there is a direct, well-documented link between high CO2 and reduced concentration and attainment, so demand-controlled ventilation keyed to CO2 sensors is the sensible core of the design. In leisure and pool halls, the challenge is humidity and condensation as much as fresh air, so the ventilation strategy is built around moisture control and protecting the fabric from damp. In offices, the priority is delivering good air quality across a variable, cellular occupancy without ventilating empty rooms — the classic case for DCV. And in any building with a commercial kitchen, dedicated grease extract runs on its own regime entirely, with the TR19 fire-safety cleaning duty that goes with it. A good design reads these duties off the building’s actual use and occupancy pattern, rather than applying a single fresh-air rate everywhere and hoping.

Sizing and economics

Ventilation is sized on the fresh-air rate the building’s occupancy requires, following CIBSE and Approved Document F guidance, not on floor area alone. Fan power typically runs from 0.5 to 20 kW, with plant space of roughly 5–60 sqm. Indicative project values run from around £8,000 for a small MVHR and demand-control scheme up to £200,000 for a large multi-zone system with extensive ductwork, controls and heat recovery. Because ventilation is one of the more affordable HVAC interventions relative to its comfort and energy payoff, it is often the first upgrade a building makes, and a natural companion to any heat-pump or AHU project. There are indicative ranges for every system type on our cost guide.

The running-cost and efficiency case

The headline efficiency metric here is heat-recovery efficiency — the proportion of exhaust heat the MVHR unit recaptures, up to around 90 per cent for a good unit. That figure, combined with the fan efficiency and the demand-control strategy, sets what ventilation costs to run. The saving is real and easy to reason about: a building that ventilates efficiently avoids paying twice — once to bring in fresh air and again to condition it. The design job is to hit the required fresh-air rate for healthy air at the lowest possible energy cost, which MVHR and demand control do together.

The indoor air quality angle — the whole point of ventilation

Indoor air quality (IAQ) is not a separate product bolted onto HVAC; it is what ventilation delivers. CO2 rising through the afternoon in an under-ventilated meeting room measurably dulls concentration; poor filtration lets in particulates and pollen; inadequate fresh air lets bioeffluents and moisture build up. Good ventilation solves all of this: adequate, filtered fresh air, CO2 kept in check by demand control, and humidity managed in wet spaces. The wellbeing, productivity and infection-control benefits of good IAQ are why more building owners now specify ventilation deliberately rather than treating it as an afterthought. The design trick — and the reason MVHR and DCV matter so much — is to deliver that air quality without a heating and cooling penalty.

The electrification and MEES tie-in — ventilation as the enabler

Ventilation is the quiet enabler of the whole electrification story, and this is its distinctive place in the strategy. A commercial heat pump delivers heat efficiently only at low flow temperatures, and low flow temperatures are only viable when the building’s heat losses are low. Uncontrolled ventilation is a major heat loss — every cubic metre of unheated fresh air pulls the building’s heat back out. MVHR recovers that heat, and demand control minimises how much fresh air needs conditioning in the first place. So low ventilation heat loss is precisely what makes low-temperature electrified heating work. In the sequence that runs through all our commercial HVAC work — efficient cooling and ventilation first, then electrify heat, then solar to power it — ventilation is the step that unlocks the ones after it.

Efficient ventilation also lifts an EPC. MVHR heat recovery and demand control improve the modelled energy performance that feeds a commercial EPC, supporting the MEES position — EPC E to let since 1 April 2023, EPC B proposed by 2031 for larger privately-rented non-domestic buildings, subject to secondary legislation (confirm the current position on gov.uk). Ventilation ductwork carries a TR19 hygiene duty for fire safety and air quality, and external plant is assessed to BS 4142 acoustic limits, with internal targets around 35 dB(A). See our grants and funding page for the capital allowances that fund the work.

Objections we hear, answered honestly

“Won’t more fresh air just push up my heating bill?” Not with heat recovery. That is exactly the problem MVHR solves — it recovers up to around 90 per cent of the heat from the air it exhausts, so you get the fresh air without paying to reheat it. Add demand control and you only condition the air the building actually needs. Ventilation and low energy cost are not in conflict when the system is designed properly.

“We already have an AHU — do we need ventilation as well?” Often the AHU is your ventilation, and the question is whether it is doing the job efficiently. Where a central AHU serves the main floor but cellular spaces are under-ventilated, local MVHR and demand control fill the gaps. We survey the whole building and its occupancy pattern before recommending anything.

“Is CO2 control really worth it?” For occupied working and learning spaces, yes. CO2 build-up measurably affects concentration and comfort, and demand control keeps it in check while cutting energy in the hours rooms sit empty. In schools and offices it is one of the clearer wins in ventilation.

Natural, mechanical and mixed-mode — matching the ventilation to the building

Not every space needs full mechanical ventilation, and a good design is honest about that. Natural ventilation — openable windows, vents and stack effect — costs nothing to run and works well in shallow-plan, low-occupancy spaces, but it offers no heat recovery, no filtration of incoming pollution, and little control on a still or cold day. Mechanical ventilation with MVHR gives filtered, heat-recovered, controllable fresh air but draws fan power. Mixed-mode designs combine the two, using natural ventilation when outdoor conditions suit and switching to mechanical, heat-recovered ventilation when they do not — often the most efficient answer for a UK office across the year. The right mix depends on the building depth, its exposure, the outdoor air quality and the control the occupants need, which is why ventilation is a design decision read off the building rather than a single product specified everywhere.

Commissioning and balancing — where ventilation is won or lost

A ventilation system only delivers its design air quality and efficiency if it is properly commissioned and balanced, and this is where a surprising number of installations quietly fail. Balancing sets the airflow to each room so that every space gets the fresh-air rate it was designed for — not too little, which leaves it stuffy, and not too much, which wastes fan and conditioning energy. An unbalanced system can look complete and still leave the far end of a duct run under-ventilated while the nearest rooms are over-served. Commissioning records document the measured airflows, the control set-points and the heat-recovery performance, giving you evidence the system meets its design and a baseline to check against in future. When we hand a system over, the balancing figures and commissioning data are part of the package, because a well-designed ventilation system that is never properly balanced delivers neither the air quality nor the efficiency it promised.

Frequently asked questions

What does MVHR do?

Mechanical ventilation with heat recovery supplies fresh air and extracts stale air through a single unit with a heat exchanger, recovering up to around 90 per cent of the heat from the outgoing air to pre-condition the incoming air. It gives you the fresh air needed for good indoor air quality while keeping most of the energy.

What is demand-controlled ventilation?

Demand-controlled ventilation (DCV) uses CO2 sensors and occupancy detection to supply fresh air only where and when it is needed, rather than ventilating every space at full rate all the time. It saves fan energy and the heating and cooling energy that would otherwise temper unnecessary air.

How does ventilation affect indoor air quality?

Directly — ventilation is what delivers fresh, filtered air and controls CO2, humidity and pollutants. Good ventilation supports concentration, wellbeing and infection control. The design goal is to deliver that air quality without a heating or cooling penalty, which MVHR and demand control achieve together.

Is ventilation linked to my heat pump project?

Closely. Low ventilation heat loss is what makes low-temperature heat-pump heating viable, so MVHR and demand control are the efficiency partner to any commercial heat pump upgrade. Getting ventilation right first is what lets the electrified heat run at a good SCOP.

Does ventilation ductwork need cleaning?

Yes. Extract and supply ductwork carries a TR19 hygiene duty for fire safety and air quality, cleaned and documented on a schedule — normally inside a PPM contract. Kitchen extract in particular is a fire-safety priority.

---

We design and install commercial ventilation and MVHR systems across the UK, including London, Manchester and Birmingham. For a ventilation and indoor-air-quality survey, request a quote, or read the most common commercial HVAC questions.