Defra’s F-Gas phase-down: what it means for onboard refrigeration

The message is clear: less high-GWP refrigerant available, stricter compliance tracking, and rising costs for legacy gases like R404A and R22.

The UK Government’s consultation on accelerating the F-gas phase-down has now closed. While we await the final outcome, the proposals (combined with changes already in force in the EU) point firmly in one direction: availability pressure will increase, and costs will rise for operators still dependent on higher-GWP refrigerants.

This isn’t a distant concern. The consultation proposes quota cuts starting as early as 2026, with the sharpest reductions hitting the highest-GWP refrigerants first. For vessels still running legacy systems, the window for cost effective, planned transitions is narrowing.

What this article covers:

• Which refrigerants are most exposed to phase-down pressure
• How much GWP reduction you get from switching
• RS drop-ins vs other low-GWP options
• What ‘genuinely moving the needle’ looks like in practice

For a deeper understanding of the legislation as it stands, see our full guide on how F-gas regulation works and what it means for onboard refrigeration.

Which refrigerants are most exposed to phase-down pressure?

Anything with a very high Global Warming Potential (GWP) sits at the sharp end of both the UK and EU phase-down curves.

A key point from the consultation is that the squeeze won’t only hit the ‘worst offenders’. Mid-GWP gases that many operators still treat as workable defaults are likely to come under increasing quota pressure too: which is why planning ahead matters, even if your system isn’t running the highest-GWP refrigerant.

R404A, R507 and R22 are already heavily squeezed, with supply increasingly reliant on reclaimed stocks. Operators are already seeing higher prices and longer lead times when systems fail unexpectedly.

What’s changed (and what many operators underestimate) is that mid-range refrigerants are next. Gases such as R410A, R407A/F and R134a aren’t disappearing overnight, but they are now clearly in the firing line as quota pressure increases.

As highlighted during the consultation process, aligning the UK more closely with the EU’s accelerated phase-down means these gases will become progressively harder and more expensive to source. Operators who still view them as ‘safe for now’ risk being caught out.

Low-GWP refrigerants at a glance

A quick reference for matching legacy gases to lower-GWP alternatives, including RS drop-in refrigerants and other options for new systems or controlled retrofits.

Which refrigerants are likely to become restricted or expensive?

Anything with a very high GWP sits at the sharp end of both phase-down curves.

R404A, R507 and R22 are already heavily squeezed, with supply relying more on reclaimed stocks. Mid-GWP gases such as R410A, R407A/F and R134a aren’t disappearing overnight, but they’re the next group likely to feel quota pressure.

For operators still reliant on R404A or R22, availability will continue to tighten – and the Defra proposals push the UK in the same direction as the new EU rules.

We’re already seeing this pattern with legacy gases, where availability is increasingly dependent on reclaimed stocks. The risk for operators is leaving action until a breakdown forces a last-minute purchase, when price and availability are at their worst.

How much GWP reduction do we get if we retrofit now?

For most legacy systems, the drop is substantial. Typical examples:

• R404A → RS-51, R448A or R449A: 50–75% reduction
• R134a → RS-20 or R513A: more than half
• R410A → R32 (new kit): about two-thirds

The exact saving depends on charge size and leakage rates, but even a straightforward retrofit usually cuts future risk dramatically.

These reductions are shown in the RS Replacement tables at the top of the page.

Which options are safe bets long-term?

For long-term compliance and cost stability, the safest options are:

• Very low-GWP refrigerants (GWP <150) in new or redesigned systems
• Natural refrigerants (CO₂ or ammonia) where the vessel’s layout, safety systems and crew competence allow
• Lower-GWP HFC/HFO blends as transitional solutions when a full system change isn’t practical yet

These options are least exposed to future restrictions or quota pressure.

Which refrigerants genuinely ‘move the needle’?

Choosing a replacement refrigerant isn’t just about performance; the size of the GWP reduction determines long-term compliance, cost stability and future availability.

The chart below compares Global Warming Potential (GWP) for common legacy gases and the main lower-GWP alternatives. It shows how far each option moves you away from the highest-impact refrigerants, helping you to see the real impact of switching:

• Legacy gases sit at the highest end of the scale
• RS drop-ins sit in the middle
• Newer HFO blends and natural refrigerants sit at the lowest end

Where do RS refrigerants sit compared to non-RS alternatives?

RS refrigerants sit firmly in the middle ground:

• Lower GWP and far less regulatory exposure than legacy gases
• Minimal system changes (for example, no changes to expansion tubes or oil needed)
• Useful when downtime is tight or major hardware changes aren’t realistic

Non-RS options like R513A, R448A/R449A or R32 can offer similar or deeper reductions, but usually involve more design considerations or new equipment.

See the RS Drop-In Replacements table at the top of this page for system-by-system guidance.

In simple terms, drop-in refrigerants can be a sensible step when downtime and system changes need to be minimal. Full system upgrades (including ultra-low-GWP or natural refrigerants) offer the strongest long-term protection, but they require more planning and, in many cases, more modification work. The right approach depends on vessel schedules, the system’s age and condition, and how long you expect to keep running the current set-up.

What next?

Still running high-GWP systems and wondering what your best next move is? With the consultation closed and changes likely ahead, now’s the right time to assess your exposure and plan a transition while options and pricing are still in your control.

Our refrigeration engineers have decades of experience helping vessel operators navigate F-gas compliance and plan cost-effective transitions. Contact us to discuss your specific requirements: no pressure, just practical advice from people who do this every day.