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.
| What GWP measures | Heat trapped by 1 kg of the gas over 100 years, relative to 1 kg of CO₂ |
|---|---|
| R-134a | GWP 1,430 — still the most common refrigerant in certified heat pump water heaters |
| R-513A | GWP ~630 — the near drop-in replacement for R-134a, same A1 non-flammable class |
| R-32 / R-1234yf | GWP ~675 and ~4 — both A2L, mildly flammable, with handling rules to match |
| R-744 (CO₂) | GWP 1 — used in split systems, runs transcritical at well over 1,000 psi |
| Charge size | Under about 2 lb in a residential heat pump water heater, against 6–12 lb in a central air conditioner |
What the number means in practice
GWP is a ratio, not a quantity. It says that leaking one kilogram of R-134a warms the climate about as much as releasing 1,430 kilograms of CO₂ over a hundred years. To turn it into something meaningful you have to multiply by the charge, and residential water heaters carry very little: typically under two pounds, against six to twelve in a central air conditioner and several ounces in a domestic fridge.
A full release of a two-pound R-134a charge is therefore roughly 1,300 kg CO₂-equivalent — comparable to driving a petrol car around 3,000 miles. Not nothing, but small next to the multi-tonne annual emissions the same appliance avoids by displacing resistance heating or gas combustion. The honest framing is that refrigerant choice is a secondary environmental consideration for this product, and a primary regulatory one.
It also only matters if the refrigerant escapes. The circuit is sealed at the factory, never opened during normal service, and residential heat pump water heaters are usually replaced rather than repaired at the sealed-system level. The realistic leak paths are a manufacturing defect, physical damage, and improper disposal at end of life — which is why recovering refrigerant at scrapping is a legal requirement rather than a courtesy.
What the certified market actually uses
R-134a still dominates: 445 of the certified models listed on this site. R-513A, a blend with roughly 630 GWP that behaves close enough to R-134a for manufacturers to switch with modest redesign, appears on 31. CO₂ shows up on 90 — almost entirely split systems with the compressor outdoors. R-1234yf accounts for 11 and R-32 for two.
Safety class matters as much as GWP when comparing them. R-134a and R-513A are A1: non-flammable, no special handling. R-32 and R-1234yf are A2L, mildly flammable, which brings charge limits, leak detection requirements in some configurations, and different service procedures. R-744 is A1 and utterly non-flammable, but operates transcritically at pressures well above 1,000 psi, so its components are built to a different standard entirely.
CO₂ systems earn their place on performance, not just on their GWP of 1. Transcritical operation produces very hot water and holds capacity in cold ambient conditions, which is why the split-system models in the certified data list compressor cutoffs down to −26 °F while integrated units mostly stop at 37 °F. The cost is complexity: an outdoor unit, a refrigerant line set, and a higher installed price.
Where the regulation is heading
The AIM Act of 2020 directs EPA to cut US production and consumption of HFCs by 85% by 2036, using an allowance system that steadily raises the price of high-GWP refrigerants. On top of that, EPA’s Technology Transitions rules set sector-by-sector GWP ceilings — 700 for residential air conditioning and heat pump equipment from 2025 — and California and several other states run parallel programmes. The direction of travel across all of them is a ceiling somewhere near 700, which R-134a fails and R-513A, R-32, and R-1234yf clear.
For a buyer this is mostly about the back half of the appliance’s life. A 15-year-old unit charged with a refrigerant that is expensive and scarce is harder and costlier to service, and any warranty repair involving the sealed system depends on the refrigerant still being available. Choosing a model that already uses a sub-700 refrigerant removes that risk without costing anything today.
What it should not do is override the decisions that actually matter. Efficiency, first-hour rating, compressor cutoff temperature, and whether the unit physically fits your space all affect your energy use and comfort far more than the GWP of a two-pound sealed charge. Treat refrigerant as a tie-breaker between otherwise comparable models.
Frequently asked questions
What refrigerant do heat pump water heaters use?
Most use R-134a, with GWP 1,430 — 445 of the certified models on this site. Newer designs use R-513A (~630), R-32 (~675), or R-1234yf (~4), and split systems commonly use CO₂, R-744, with a GWP of 1. The refrigerant is listed in the certification record and on every heat pump model page here.
Does refrigerant GWP matter if the system never leaks?
Environmentally, much less than the headline number implies: the charge is under two pounds and stays sealed, so the realistic risk is a defect or improper disposal. Commercially it matters more, because the HFC phasedown is making high-GWP refrigerants scarce and expensive, which affects what a sealed-system repair costs ten years from now.
Is a CO₂ heat pump water heater better?
For cold climates, often yes — CO₂ split systems hold capacity at low ambient temperatures, with certified compressor cutoffs down to −26 °F where integrated units typically stop at 37 °F, and they produce hotter water. They also carry a GWP of 1. The trade-offs are a higher installed cost, an outdoor unit with a refrigerant line set, and very high system pressures that require specialist service.
Are A2L refrigerants like R-32 safe in a water heater?
Yes, within their design rules. A2L means mildly flammable — hard to ignite and slow to burn compared with a hydrocarbon — and equipment using them is designed to charge limits, with leak detection or ventilation where codes require it. The relevant practical difference is for service technicians, not homeowners.
Will R-134a be phased out?
It is being squeezed rather than banned outright. The AIM Act phases US HFC supply down 85% by 2036, and sector rules are pushing new equipment below roughly 700 GWP, which R-134a exceeds. Existing units keep working and refrigerant remains available for service, but it becomes progressively more expensive over the life of the appliance.