What Is Decentralised MVHR? A Guide to dMVHR Ventilation
What Is Decentralised MVHR? A Guide to dMVHR Ventilation
Mechanical Ventilation with Heat Recovery (MVHR) is commonly associated with a central unit and ductwork running throughout a property. However, this is not the only way to benefit from heat recovery ventilation.
Decentralised Mechanical Ventilation with Heat Recovery (dMVHR) provides ventilation and heat recovery on a room-by-room basis, making it a useful option where installing a traditional whole-house ducted MVHR system may be difficult.
What Is Decentralised MVHR?
Decentralised MVHR, often shortened to dMVHR, uses individual heat recovery ventilation units installed directly through external walls.
Unlike a traditional MVHR system, which normally uses one central unit connected to multiple rooms through ductwork, decentralised systems ventilate individual rooms or zones.
A dMVHR unit typically extracts warm, stale air from inside the property while recovering heat that would otherwise be lost. This recovered heat is then used to help warm incoming fresh air.
This allows the property to receive controlled ventilation while reducing unnecessary heat loss.
How Does dMVHR Work?
The exact operation depends on the unit selected, but decentralised heat recovery units generally use fans and a heat exchanger or regenerative heat store to exchange heat between outgoing and incoming air.
Some units provide simultaneous supply and extract ventilation, while other decentralised systems operate in cycles, alternating between extracting stale air and supplying fresh air.
Certain units can also be installed in pairs or groups so that several rooms work together as part of a wider ventilation strategy.
Because the ventilation equipment is located directly within the room, there is usually much less ductwork required than with a central MVHR installation.
When Is Decentralised MVHR Useful?
One of the main advantages of decentralised mechanical ventilation with heat recovery is installation flexibility.
dMVHR can be particularly useful for:
- Existing homes and retrofit projects
- Apartments and flats
- Individual rooms requiring improved ventilation
- Properties where there is limited space for ductwork
- Renovations where opening ceilings and floors would cause significant disruption
For a new build or major renovation where suitable duct routes are available, a central MVHR system may still be the preferred solution. However, decentralised ventilation can provide an alternative where a full ducted system is impractical.
For smaller or room-specific applications, explore our Single Room MVHR units.
What Are the Benefits of dMVHR?
Heat Recovery
Rather than simply extracting heated indoor air directly outside, dMVHR systems recover a proportion of the heat from the outgoing air and use it to temper incoming fresh air.
Reduced Ductwork
Because units are installed locally, decentralised MVHR generally requires significantly less internal ductwork than a central whole-house system.
Suitable for Retrofit
This reduced ductwork requirement can make dMVHR particularly attractive when upgrading the ventilation in an existing property.
Controlled Fresh Air
Mechanical ventilation provides a controlled method of introducing fresh air and removing stale air rather than relying entirely on opening windows.
Room-by-Room Installation
Depending on the ventilation design, units can be used to target specific areas or installed across multiple rooms to create a decentralised ventilation system.
dMVHR vs Central MVHR
The main difference is how the ventilation is distributed.
A central MVHR system uses one main heat recovery unit and a network of ductwork to supply and extract air throughout the property.
A decentralised MVHR system instead uses individual units positioned in external walls, reducing the need for extensive internal ductwork.
Neither approach is automatically suitable for every property. The correct choice depends on factors including the building layout, airtightness, required airflow rates, available installation space and whether the project is a new build or retrofit.
You can read our What Is MVHR? Heat Recovery Ventilation Systems Explained guide for a more detailed introduction to traditional MVHR.
Does dMVHR Meet Building Regulations?
Ventilation should always be designed to provide the airflow required for the property and comply with the regulations applicable to the project.
In England, Approved Document F provides guidance on meeting Building Regulations requirements for ventilation. Requirements and guidance can differ across England, Northern Ireland, Scotland, Wales and the Republic of Ireland, so the relevant local requirements should always be checked before selecting or installing a system.
Choosing a Decentralised MVHR Unit
When comparing dMVHR or single-room heat recovery units, consider more than simply the size of the unit.
Important factors include:
- Required airflow
- Heat recovery performance
- Noise levels
- Installation location
- Controls and operating modes
- Filter requirements
- Wall thickness and installation requirements
- Whether units need to operate individually or as a paired system
The ventilation solution should ultimately be selected around the requirements of the building rather than choosing a unit based only on its maximum airflow.
