TL;DR:

  • R32 is the mainstream choice: widely available, compatible with most MCS-certified installers, higher GWP than R290 but still 68% lower than the R410A it replaced
  • R290 (propane) has near-zero GWP and better thermodynamic efficiency at low temperatures, but requires A3 flammable refrigerant handling certification and has stricter charge size limits
  • For most UK homeowners, R32 is the practical choice in 2026; R290 becomes more compelling as installer certification improves and EU F-gas regulations tighten

Why Refrigerant Choice Is Becoming a Real Decision

For most of the past decade, UK heat pump buyers didn’t need to think about refrigerants. The industry ran on R410A, and then R32, and the choice was made for them by whatever model their installer stocked.

That’s starting to change. The EU F-Gas Regulation 2024 is accelerating a phase-down of high-GWP refrigerants across the EU, and while the UK has its own F-Gas regime post-Brexit, UK manufacturers and the supply chain are tracking EU timelines because most heat pump equipment is EU-manufactured. R290 systems are increasingly prominent in the product ranges of Daikin, Samsung, and Vaillant — brands that have dominated UK ASHP installations.

Understanding the difference between R32 and R290 is now a legitimate homeowner question, particularly for buyers planning a 15-20 year installation and thinking about lifecycle regulatory risk.

The Basics: What These Refrigerants Are

R32 (difluoromethane, CH₂F₂) is a hydrofluorocarbon (HFC) with a Global Warming Potential (GWP) of 675 over 100 years, compared to 2,088 for R410A. It is mildly flammable (A2L safety classification) at high concentrations but not in typical operating conditions. The vast majority of heat pumps installed in the UK in 2024-2026 use R32.

R290 (propane, C₃H₈) is a hydrocarbon refrigerant with a GWP of 3 — effectively negligible from a climate perspective. It is highly flammable (A3 safety classification), which creates real handling and installation constraints. It also has excellent thermodynamic properties, particularly at sub-zero outdoor temperatures.

Efficiency at Low Outdoor Temperatures

R290’s thermodynamic profile gives it meaningful advantages in cold UK winters. Propane has a higher volumetric refrigerating capacity than R32, meaning a smaller compressor can do the same work. This translates to better Seasonal Coefficient of Performance (SCOP) at temperatures from +7°C down to -15°C — exactly the range where UK heat pumps need to perform well.

Manufacturers currently producing R290 systems report SCOP values 5-10% above comparable R32 units in the same class. This is a real efficiency gain, though the exact number varies significantly by model, installation, and house heat demand profile. For a well-insulated UK home with radiators sized for 45°C flow temperatures, the practical annual energy cost difference on an R290 unit is likely to be modest — a few percentage points.

At very low temperatures (below -15°C), R290’s advantage becomes more pronounced. This matters less for southern UK but is relevant for Scottish installations.

Safety and Installation Implications

This is where the practical difference between R32 and R290 is most significant for 2026 UK installations.

R32 (A2L): Mildly flammable but will not ignite under normal operating conditions. Handling requires F-Gas certification (Category I for systems over 3kg), which most UK heat pump engineers hold. System design and siting follow standard MCS guidelines. No special room requirements for indoor units in residential settings.

R290 (A3): Highly flammable. Handling requires specific A3 flammable refrigerant certification. Charge sizes per system are limited under EN 378 to restrict the quantity of flammable gas in any single space — current limits for domestic indoor installation are around 1kg, though this is under review. Outdoor-only or well-ventilated siting is effectively required. Leak detection may be recommended by manufacturers.

The installer pool for R290 residential systems in the UK is smaller than for R32. This is not a permanent barrier — training programmes are expanding and several manufacturers are offering R290 certification as part of their installer programmes — but in 2026 it means longer waits, potentially higher installation costs, and fewer options for comparison quotes.

Environmental and Regulatory Outlook

The UK F-Gas Regulation currently follows a phase-down trajectory for HFCs based on GWP. R32 (GWP 675) sits above many transition targets but is not immediately under pressure at the domestic scale. Commercial refrigeration is facing more acute phase-down timelines.

The EU F-Gas Regulation 2024 is more aggressive, with restrictions on systems using refrigerants above GWP 150 in certain new product categories from 2027. Because most heat pumps sold in the UK are manufactured to EU specifications, EU timelines effectively determine when manufacturers transition their product lines. Several major manufacturers have stated intent to shift primary ASHP lines to R290 by 2027-2028.

For UK homeowners, this creates a mild timing consideration: an R32 system installed today is compliant and will remain so throughout its operational life. But a 2027-2028 replacement cycle would likely fall on R290 products. If you’re on the fence, neither choice is wrong — R32 systems will be maintained and refilled legally for many years.

Charge Sizes and System Design

Most UK residential ASHPs use between 1.5kg and 3kg of refrigerant. Both R32 and R290 systems in domestic sizes fall within typical charge ranges, though R290’s flammability limits are more constraining on charge size, which can affect system design for larger homes or high-demand installations.

For split systems (separate indoor unit and outdoor unit connected by refrigerant pipework), charge size increases with pipe run length. R290 systems typically come factory-charged and sealed by the manufacturer; field-charged R290 systems with long pipe runs require careful engineering and A3-certified handling.

Monobloc heat pumps — all refrigerant components in the outdoor unit — have a simpler regulatory profile for R290 because the flammable refrigerant is never brought indoors.

Which to Choose in 2026

R32 is the default for most UK homeowners in 2026. The installer pool is larger, quotes are easier to get, and every major MCS-certified installer can handle it. The environmental credentials are meaningfully better than the R410A systems it replaced, and the efficiency difference from R290 won’t matter in most installations.

R290 is worth pursuing if:

  • You’re building new or doing a major refurbishment where installer access, ventilation, and system siting can be designed from scratch
  • You’re in Scotland or northern England where winter performance gains are more significant
  • You have a straightforward monobloc installation with a short outdoor run
  • Environmental credentials are a priority and you’re willing to wait for a qualified installer

For either refrigerant: Ensure your installer holds current MCS certification and the appropriate F-Gas category. Ask specifically whether they hold A3 certification if you’re considering R290. The refrigerant choice matters, but it’s secondary to getting a correctly sized, well-installed system with appropriate flow temperature settings for your radiators or underfloor heating.