Refrigerant GWP
GWP (global warming potential) measures how strongly a refrigerant traps heat if leaked, relative to CO₂. Older HPWHs use R-134a (GWP 1430); newer models use R-513A (~630), R-32 (~675), or CO₂ itself (GWP 1) as regulations phase high-GWP refrigerants out.
The refrigerant sits sealed inside the compressor circuit and only matters environmentally if it leaks or is disposed of improperly — but US and state regulations are steadily pushing manufacturers toward low-GWP alternatives.
For buyers the practical takeaway: a low-GWP refrigerant future-proofs service and refrigerant availability, and CO₂ (R-744) units double as the cold-climate performance leaders.