If you have been researching heat recovery units - also known as MVHR systems, heat recovery ventilators, or recuperators - you will quickly find that the terminology can be confusing, the technical specifications dense, and the range of products bewildering. This guide cuts through the complexity and gives you a clear, practical framework for choosing the right system for your building.
What Is a Heat Recovery Unit?
A heat recovery unit - more formally called a Mechanical Ventilation with Heat Recovery (MVHR) system - is a ventilation device that does two things simultaneously: it extracts stale, moist air from inside a building, and supplies fresh, filtered air from outside. The clever part is what happens in between.
Inside the unit, the outgoing and incoming air streams pass through a heat exchanger without mixing. The warmth from the outgoing stale air is transferred to the incoming fresh air before it enters the room. The result: you get continuous fresh air without losing the heat you have already paid to generate.
A good heat recovery unit recovers between 90% and 97% of the heat that would otherwise be lost through conventional ventilation. Over a heating season, this translates into a meaningful reduction in energy bills - particularly in well-insulated or airtight buildings where the unit is running continuously.
Why Does Ventilation Matter?
Modern buildings are increasingly airtight. New builds in particular are constructed to very high air tightness standards, which is excellent for energy efficiency but creates a problem: without deliberate ventilation, stale air, moisture, CO2, allergens, and pollutants build up indoors.
The consequences of poor ventilation include:
- Condensation and mould growth - particularly in bathrooms, kitchens, and bedrooms
- High indoor CO2 levels causing fatigue, poor concentration, and disrupted sleep
- Elevated humidity encouraging dust mites and allergens
- Build-up of volatile organic compounds (VOCs) from furniture, cleaning products, and building materials
- Poor air quality that exacerbates asthma and respiratory conditions
Opening windows solves the ventilation problem but creates an energy problem - particularly in winter, when you lose significant heat every time a window is opened. A heat recovery unit solves both problems simultaneously: continuous fresh air, with minimal heat loss.
Types of Heat Recovery System
Decentralised Single-Room Units
These are compact units installed directly through an external wall, serving a single room. They require no ductwork - just a 160mm to 220mm core drill through the external wall. Installation typically takes two to four hours per unit and can be carried out as a retrofit in any existing property.
Decentralised units are ideal for:
- Individual rooms in existing homes - particularly bedrooms, living rooms, and home offices
- Retrofit projects where whole-house ducting is impractical
- Flats and apartments where running ductwork between rooms is not possible
- Commercial spaces where individual room ventilation is preferred
The Prana range - available from Veralis - is a leading example of the decentralised approach. Using a copper heat exchanger (which is both more efficient and naturally antiseptic compared to aluminium or plastic alternatives), Prana units achieve heat recovery efficiency of up to 97% while consuming as little as 3-17 watts of electricity - less than a standard lightbulb.
Centralised Whole-House MVHR Systems
These are larger units, typically installed in a loft, utility room, or plant room, connected to ductwork that runs throughout the building. They provide balanced ventilation for the whole property from a single unit.
Centralised systems are ideal for:
- New build residential properties
- Major refurbishments where ductwork can be incorporated during construction
- Commercial buildings requiring whole-building ventilation management
The trade-off is installation complexity and cost - centralised systems require significant ductwork and are generally better suited to new build than retrofit.
How to Choose the Right Heat Recovery Unit
Step 1 - Assess your building type
Is it a new build or an existing property? A single room or whole building? Are you able to install ductwork? For the majority of retrofit residential projects and individual commercial rooms, a decentralised unit is the practical choice. For new builds and major commercial projects, a centralised system should be specified.
Step 2 - Measure your room volume
Heat recovery units are rated by their airflow capacity, measured in cubic metres per hour (m³/h). To calculate the airflow you need, multiply the room's floor area by its ceiling height to get the volume, then multiply by the recommended air change rate (typically 0.5 to 1.0 air changes per hour for residential use).
For example: a 20m² bedroom with a 2.4m ceiling has a volume of 48m³. At 0.5 air changes per hour, you need 24m³/h minimum airflow - comfortably within the range of the Prana 160 MINI (up to 70m³/h).
Step 3 - Consider wall thickness
Decentralised units require a core-drilled hole through the external wall. Different models accommodate different wall thicknesses. The Prana range covers wall thicknesses from standard cavity walls up to 500mm+ with extension tubes available. Always check the installation requirements for your specific wall construction before purchasing.
Step 4 - Consider noise levels
If the unit is to be installed in a bedroom, noise is a primary consideration. Look for units with a dedicated night mode that reduces fan speed and airflow for quiet overnight operation. The Prana range operates at 8 dB(A) on its lowest setting in night mode - quieter than a whisper.
Step 5 - Consider controls and smart features
Modern heat recovery units can be controlled via smartphone app, allowing you to monitor air quality, adjust fan speeds, set schedules, and switch between modes remotely. If you value smart home integration or want to monitor CO2 and humidity levels in real time, look for units with WiFi connectivity and app control.
The Prana Range - Decentralised MVHR for Homes and Offices
Veralis stocks the Prana range of decentralised heat recovery ventilation units - among the most technically advanced single-room MVHR systems available in the UK.
Key features across the Prana range:
- Copper heat exchanger - copper is a more efficient heat conductor than aluminium and is naturally antiseptic, inhibiting bacterial growth within the unit
- Up to 97% heat recovery efficiency - among the highest available for a decentralised unit
- 3 to 91 watts consumption depending on fan speed - typically less than a standard lightbulb
- Night mode - ultra-quiet operation (from 8 dB) for undisturbed sleep
- WiFi and smartphone app control (Prana app) - monitor and adjust from anywhere
- Auto mode - automatically adjusts airflow based on room conditions
- Winter mode - prevents heat exchanger freezing in temperatures down to -25°C
- Operating range -25°C to +40°C - suitable for UK climate year-round
- Summer bypass - reduces heat recovery in warm weather to allow cooler air in
- Filter included - removes dust, pollen, and allergens from incoming air
Prana models available:
The Prana 160 MINI is the compact entry-level model, suitable for smaller rooms up to 20m². With a 162mm core-drill requirement and a working module length of 450mm, it suits standard UK cavity wall construction.
The Prana 160 ERP PRO is a more advanced model with enhanced energy performance rating (ERP) classification, CO2 sensing, and more sophisticated auto control. Suitable for bedrooms, home offices, and living rooms.
The Prana 210G covers larger rooms up to 30m² with higher airflow capacity (up to 85m³/h) and achieves up to 97% heat recovery efficiency.
Installation - What to Expect
Decentralised units like the Prana are designed for relatively straightforward installation:
- Core drill - a single hole is drilled through the external wall to the diameter specified for the unit (typically 162mm for the Prana 160, 220mm for the Prana 210)
- Sleeve installation - a sleeve is inserted into the core-drilled hole
- Unit installation - the unit slides into the sleeve and is secured
- Connection - the unit connects to a standard 230V power socket
- App setup - connect to WiFi and configure via the Prana app
A competent DIY installer can fit a single unit in two to four hours. Professional installation is also available.
Wall thickness considerations: The standard Prana working module is 450mm long. Extension tubes are available for thicker walls. If your wall is thicker than the standard unit length, contact us before ordering to confirm the correct configuration.
Heat Recovery Units vs Other Ventilation Options
| System | Heat Recovery | Installation | Best For |
|---|---|---|---|
| Opening windows | None | None | Occasional ventilation only |
| Extract fans | None | Simple | Bathrooms and kitchens |
| Positive Input Ventilation (PIV) | None | Moderate | Whole-house damp control |
| Single-room MVHR (Prana) | Up to 97% | 2-4 hours per room | Retrofit, individual rooms |
| Whole-house MVHR | Up to 95% | Complex | New build, major refurb |
Frequently Asked Questions
How long do heat recovery units last? Quality units like the Prana range are designed for 15-20+ years of continuous operation with routine filter maintenance. The copper heat exchanger requires no maintenance beyond periodic cleaning.
Do heat recovery units require planning permission? In most cases, no. Single-room decentralised units require only a small hole through the external wall, which typically falls within permitted development rights. For listed buildings or properties in conservation areas, check with your local planning authority.
How often do filters need replacing? This depends on local air quality and usage levels. Most manufacturers recommend checking filters every three to six months and replacing annually. Units with filter life indicators take the guesswork out of maintenance.
Can I install a Prana unit myself? Yes, provided you are comfortable using a core drill and following the installation instructions. The electrical connection uses a standard 230V socket - no specialist electrical work required. If you are unsure, a local handyman or builder can carry out the installation.
What wall thickness does the Prana 160 accommodate? The standard Prana 160 working module is 450mm long. Extension options are available for thicker walls. Contact us with your wall construction details and we will advise on the correct configuration.
Will a heat recovery unit remove cooking smells? Yes - continuous air exchange significantly reduces the build-up of cooking odours, as well as other household smells. For kitchens specifically, ensure adequate airflow capacity for the room size.
Do heat recovery units work in winter? Yes. Prana units are rated for operation in temperatures down to -25°C. Winter mode prevents the heat exchanger from freezing in very cold conditions.
Shop Heat Recovery Units at Veralis
We stock the Prana range of decentralised MVHR units, alongside a wider selection of ventilation equipment for residential and commercial applications.
For help choosing the right unit for your project, call us on 0330 122 1023 or email contact@veralis.co.uk. We are happy to advise on model selection, wall thickness compatibility, and installation requirements.
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Veralis is a trading name of Blueberry You Ltd, registered in England and Wales (Company No. 16716333). Free UK delivery on orders over £500.
