The refrigerant revolution: what you should know about low-GWP for MVHR systems

Refrigerants are becoming a critical factor in Part O overheating strategies, and their importance will only grow as the UK pushes toward low-carbon cooling and heating. Part O prioritises passive measures (orientation, glazing, shading, ventilation), but many developments need mechanical cooling.

Excess heat should be removed by opening windows, ventilation louvres in external walls, mechanical ventilation systems, and mechanical cooling systems. Passive means should be used as far as reasonably practicable, and mechanical cooling should only be permitted if requirement O cannot be met by other means.

In airtight or overheating-prone homes, passive ventilation is often not enough. That is where active Mechanical Ventilation with Heat Recovery (MVHR) systems can support performance targets. As regulations tighten, the refrigerant embedded in the system you specify can have long-term implications for compliance, safety and sustainability.

The problem with traditional refrigerants

Refrigerants such as R410A (GWP ~2088) and R134a (GWP ~1430) have been widely used in domestic HVAC systems, but they are no longer considered viable in the long term.

• They have high global warming potential (GWP)
• They are subject to F-Gas phase-downs in both the UK and EU
• They are not compatible with many net-zero housing strategies

What is GWP and how is it measured?

GWP stands for global warming potential. It measures how much heat a gas traps in the atmosphere compared to carbon dioxide (CO₂), which has a GWP of 1.

For example, a refrigerant with a GWP of 1430 has the same warming effect as 1,430 kilograms of CO₂ per kilogram released.

New regulatory pressure

The Kigali Amendment and updated F-Gas regulations are moving the industry toward refrigerants with GWP below 750, and in some cases below 150.

As a result, systems that rely on traditional refrigerants are becoming more difficult to specify, more expensive to maintain and less aligned with regulatory expectations.

What is different about MVHR systems with refrigerants

A domestic MVHR unit transfers heat between outgoing stale air and incoming fresh air using a heat exchanger. In winter, warm exhaust air preheats cold supply air, while in summer, warmer outdoor air can be pre-cooled if the indoor exhaust air is cooler—no refrigeration, no compressor — just heat exchange.

An MVHR can pre-cool air in summer, but only if conditions allow. MVHR can provide cooling recovery when:

• Indoor air is cooler than outdoor air
• The unit is not in summer bypass mode
• The heat exchanger transfers “coolth” from exhaust to supply air

For example, if the outside air temperature is 30 °C and the inside air temperature is 23 °C, the supply air after MVHR can equal ~25–26 °C (depending on efficiency). So the incoming air is cooler than outdoors, but still warmer than the room.

However, in certain applications – such as overheating-sensitive dwellings or schemes falling under Part O – specifiers are increasingly turning to active MVHR systems that include integrated cooling modules. These systems help condition incoming air while maintaining energy efficiency.

This introduces added complexity in terms of GWP, safety classification, installer certification and fire strategy – all of which are determined by the refrigerant embedded in the system.

Low-GWP alternatives emerging

Several lower-GWP refrigerants are gaining traction in residential ventilation and cooling systems. Each has trade-offs in terms of cost, safety and system design.

The table shows that R32 sits between legacy and next-generation refrigerants for domestic properties. Compared with R410A, it offers a significantly lower GWP (675 vs 2088) and higher efficiency. However, it is classified as A2L (mildly flammable), meaning installers must follow additional safety and ventilation requirements in homes. 

When compared to R290 (propane), R32 is significantly less flammable and therefore easier to deploy at typical domestic charge sizes; however, it cannot match propane’s ultra-low GWP of 3 and its environmental performance. 

Propane delivers excellent efficiency but, as an A3 highly flammable refrigerant, is subject to strict charge limits and design constraints in residential settings. 

Overall, R32 is widely seen as a pragmatic transitional choice for homes, balancing manageable safety considerations with improved climate impact, while R290 represents a more future-proof but operationally restrictive option due to its higher flammability.

Practical challenges in transitioning

As MVHR systems begin to integrate cooling, pre-construction teams face new technical and delivery challenges.

Safety and fire strategy

• Refrigerants with A2L or A3 classifications may present flammability risks
• Charge size limits can restrict how and where systems can be used
• Additional containment, ventilation or spacing may be required

Installer readiness

• F-Gas certification is mandatory for refrigerant handling
• A2L and A3 refrigerants may require additional installer training and commissioning procedures

System design

• Low-GWP refrigerants often require sealed systems with reduced charge volumes
• Leak detection and fail-safe controls are needed in residential settings

Cost and complexity

• Systems using low-GWP refrigerants may require more robust components
• Greater documentation and handover requirements can affect programme delivery

Introducing Titon HRV Cool Plus

To address the need for effective cooling without added site-side refrigerant risk, Titon has developed the HRV Cool Plus system. It offers enhanced comfort performance in modern homes while simplifying installation and compliance.

This unit delivers up to 3.14 kW of cooling through a fully sealed R32 refrigerant circuit integrated directly into the MVHR unit. It is engineered for warm-weather performance and aligns with the ventilation and overheating mitigation goals set out in Approved Document O.

Key benefits include:

• No on-site refrigerant handling - Sealed for life circuit 
• No special installer certification required
• Minimal maintenance with a proven, sealed refrigerant loop
• Wall or floor-mounted options with compact form factor especially utility cupboards 
• Fully compliant with Part O, Part F and Part L of the Building Regulations
• Mounting for both wall and floor solutions with an upgrade option to integrate a washing machine under the unit to maximise space in utility cupboards

The system supports intuitive controls, pre-set temperature cycling and active communication between the MVHR and the cooler module. Designed with residential integration in mind, it offers a practical way to add cooling performance without compromising on project delivery or long-term sustainability goals.

In summary: start the refrigerant conversation early

Refrigerant selection is no longer a detail buried in M&E. It affects fire safety, compliance pathways, installer training and sustainability outcomes.

By addressing refrigerant strategy early and matching the system to your project’s needs, you can:

• Simplify approvals
• Avoid installation risks and handover delays
• Meet client expectations for comfort and environmental performance

Need support selecting the right cooling solution? Titon offers technical advice, CPDs, and product guidance for specifiers designing all-electric or overheating-sensitive schemes.

Find out more on our website, or contact us now.