Designing an MVHR system in 2026 is a structured process, not a set of guesses with a duct calculator. For UK contractors, consultants and facilities teams, following a clear sequence reduces redesigns, keeps building control on side and cuts post‑handover complaints about noise or stuffy rooms.
MVHR System Design: Step By Step Guide
This guide is organised as a step by step process you can follow on any project. Each step explains what to check, what to decide and where products from eFans can help while keeping the focus firmly on good design practice.
Step 1: Project requirements and brief
Before choosing any MVHR unit, clarify what the project actually needs in terms of building type, occupancy patterns, airtightness targets and client priorities on cost, energy and carbon. This design brief becomes the benchmark for later decisions and helps avoid scope creep.
For non domestic or mixed use schemes, decide which zones truly need MVHR and which can use simpler mechanical extract or single room heat recovery. This prevents over designing centralised systems where localised solutions would be more practical and easier to maintain.
Step 2: Ventilation rate calculations
Once the brief is clear, calculate the required ventilation rates using current UK Building Regulations guidance and any project specific standards. In most projects this means combining whole dwelling or room by room Part F calculations with agreed air change per hour or l/s per person targets.
For trade teams, it helps to document both continuous and boost rates per room and per system. This gives a clear duty point for later unit selection and duct sizing, and makes sign off with building control and consultants more straightforward.
Step 3: Choosing the MVHR system type
With ventilation rates defined, choose the type of MVHR system that fits the building. Centralised whole house MVHR often suits flats, houses and PBSA, while larger or more complex buildings may require several units serving different zones.
Retrofit projects or isolated wet rooms sometimes work better with decentralised or single room heat recovery where duct routes are restricted.
eFans stocks a full range of heat recovery and MVHR units from Vent Axia, Zehnder, Elta and S&P. From compact through the wall units for single bathrooms or kitchens through to centralised systems with efficiencies up to 93 percent and airflows from 32 m³/h to 900 m³/h, so the system type can follow the design rather than the other way round.
Step 4: MVHR unit sizing and selection
Translate the calculated airflows into a specific unit size that can deliver the duty at realistic external static pressure. The aim is to operate the fans in their efficient range while leaving enough headroom for filter loading and possible future changes in use.
Many designers select a unit that can provide roughly 20 to 30 percent more airflow than the calculated duty at the chosen pressure.
When clients question why a more efficient or slightly larger unit is being proposed, it can help to walk them through a clear breakdown of typical MVHR costs from installation through to long term running and maintenance so they can see how efficiency, fan power and filter costs affect payback over the life of the system.
Step 5: Intake and exhaust terminal planning
With a provisional unit in mind, plan the positions of fresh air intake and exhaust terminals. Good practice keeps intake louvres away from sources of pollution, odours and exhausts, and avoids any recirculation between intake and discharge.
Consider roof versus façade locations, prevailing winds, noise impact on neighbours and safe maintenance access. Addressing these issues at design stage is far easier than relocating terminals after complaints about smells or noise once the building is occupied.
Step 6: Ductwork routing and layout
Next, design the main duct routes between the MVHR unit and the rooms served. Aim for short, direct runs with as few bends as possible, using smooth radius fittings and minimising flexible ducting which adds resistance and can generate noise.
Decide between a traditional branch layout or a radial manifold system. Radial layouts with small diameter ducts to each room often work well for dwellings and PBSA because they simplify balancing and reduce cross talk, while larger commercial and non domestic buildings usually rely on main ducts with branches and correctly placed attenuators.
Step 7: Duct sizing and noise control
Once the layout is fixed, size the ducts to keep air velocities in sensible ranges for comfort and noise control. Lower velocities are preferred on supply ducts serving bedrooms and quiet spaces, while slightly higher velocities may be acceptable on extract from kitchens and bathrooms.
Plan acoustic treatment at the same time as sizing, including attenuators near the unit and possibly before sensitive rooms, and consider breakout noise in ceiling voids.
If your work is mainly in schools, offices or other non domestic schemes, take a look at our detailed guide to commercial MVHR and heat recovery ventilation for non domestic buildings which covers noise criteria, duct sizing and regulatory expectations in more depth.
Step 8: Zoning strategy and controls
With airflow and ductwork defined, develop the zoning and control strategy. In dwellings, best practice is to supply to habitable rooms and extract from wet rooms, with boost controlled by humidity, occupancy or user switches.
In commercial and multi residential buildings, grouping areas with similar usage on the same MVHR unit or zone simplifies control and maintenance. Facilities teams generally benefit from straightforward, intuitive controls with clear filter change alerts rather than complex BMS setups that nobody adjusts after commissioning.
Step 9: Coordination with airtightness and fabric
MVHR design must integrate with the building’s airtightness and thermal strategy. The more airtight the envelope, the more the MVHR system can control ventilation and recover heat efficiently.
Coordinate early with architects and the main contractor to manage penetrations, airtightness details and insulation around ducts, especially where they pass through cold spaces or roofs.
In retrofit work, accept that airtightness may be constrained and consider whether a mix of central MVHR, decentralised units or background ventilation gives the most robust outcome for indoor air quality.
Step 10: Installation best practice on site
Once the design is agreed, installation quality determines whether the system performs as intended. Mount MVHR units level on appropriate supports, use anti vibration measures where needed and ensure condensate drains are correctly trapped, sloped and protected against freezing.
On the ductwork, avoid crushed or over‑extended flexible ducts, seal all joints carefully and label supply and extract routes clearly for future maintenance.
Provide enough access space around the unit to change filters, clean the heat exchanger and replace fans if needed, which is particularly important for facilities managers responsible for long term operation.
Step 11: Commissioning and balancing
Commissioning is the step that turns design drawings into a working system. Measure supply and extract flows at each terminal using suitable instruments, adjust dampers and unit speeds to achieve the design figures and document the results for handover.
Carry out tests at realistic operating speeds rather than maximum fan speed, checking noise levels in bedrooms and quiet zones as part of the process. Provide clear O&M manuals and a simple user guide so occupants and maintenance teams can understand filter intervals, control settings and any seasonal adjustments.
Step 12: Brand and model optimisation
With a proven design method, choosing between brands becomes a matter of matching performance, features and budget. Vent Axia and Zehnder often suit projects that prioritise very high efficiency and sophisticated controls, while Elta and S&P units can be ideal for robust plant room installations or more demanding commercial duties.
For side by side performance comparisons and product shortlists, take a look at our list of the best MVHR systems for UK projects.
Frequently Asked Questions
When is single room heat recovery preferable to central MVHR?
Single room heat recovery is often best for small spaces, retrofit projects or isolated wet rooms where running full ductwork would be too disruptive or expensive. Central MVHR is usually better for new build or deep retrofit schemes where you can plan duct routes and want consistent whole dwelling ventilation.
How can I allow for future changes in occupancy or use?
Allow a sensible margin in airflow calculations and unit sizing, often 20 to 30 percent above initial duty, and design flexible zoning and controls. This way, if occupancy increases or use changes, the system can operate at higher speeds or different schedules without major physical alterations.
What handover documentation should accompany an MVHR system?
Provide as installed drawings, commissioning records with measured airflows, unit manuals, filter specifications and a concise user guide. This package helps facilities teams maintain performance and offers evidence for building control or warranty queries.
Can MVHR systems help reduce overheating risk?
MVHR systems are primarily for ventilation and heat recovery, so they do not replace active cooling. They can however support overheating strategies by providing controlled night time purge ventilation if the design includes higher airflow settings for cooler periods and the ductwork is sized to handle those rates.