Refrigerant Leakage from Heat Pumps: Is It Sabotaging Our Carbon Reduction Goals?

R-410A is the most common refrigerant used in space conditioning heat pumps and variable refrigerant flow (VRF) systems (at least for now, in early 2025), and it has a global warming potential (GWP) of about 2,000 times that of CO₂.

If this refrigerant just stays inside a heat pump for its entire lifespan, and if this refrigerant is recovered responsibly at the end of the heat pump’s life, no worries. But that certainly doesn’t always happen.

How Much Refrigerant Leaks?

It’s very hard to estimate how much refrigerant leaks from the millions of systems out there.

A Maine program estimates that an average of 1-3% of refrigerant leaks each year from residential systems (PDF). Some California program “assumptions” list 5.3% leakage per year from residential heat pumps, but they also say that at the end of a heat pump’s lifespan, 80% of the refrigerant leaks on average (PDF).

These programs do their best to quantify the leakage, but the range is huge and it’s not an easy value to measure. It’s hard to believe these numbers are more than educated guesses.

What Are the Climate Implications of Refrigerant Leakage?

Let’s take a moderately efficient home in a colder climate that needs 20 MMBtu of heating each year. Heating the home with a fairly efficient gas system would require about 235 therms per year. Burning that gas each year results in 2,750 lbm of CO₂ emissions. How does the impact of refrigerant leakage compare?

This fairly efficient home may use two 1-ton heat pumps with a total refrigerant charge of about 7 lbm. An oversized system (which is quite common, unfortunately) might be a 3-ton, 4-zone heat pump with a charge of 12 lbm. The CO₂e emissions and leakage implications of R-410A are shown in this table:

The lower-right number—2,660 lbm—is especially concerning. If these leakage assumptions are accurate…

Lifetime CO₂e from R-410A leakage would be just about equal to that of the CO₂ emitted from burning natural gas.

Of course, this is oversimplified and generalized. Systems with good installation, operation, and maintenance should release trivial amounts of refrigerant. But there are also heat pump owners who recharge their systems every year because the refrigerant keeps leaking—which results in much more climate impact than heating with fossil fuels. These numbers do not include any CO₂ emitted from electricity generated to power the heat pumps. And most buildings heated with fossil fuels will still use refrigerant for air conditioning, and yes, some of this will leak.

This is not a straightforward issue to quantify, but there are some straightforward solutions.

How Do We Stop Refrigerant Leakage?

Install systems properly with rigorous attention to leak prevention.

SWA’s Commissioning Agents, Functional Testing Agents, and Home Energy Rating System (HERS) Raters regularly work with installers to verify tests for leakage and proper refrigerant charge.

Properly size heat pumps.

Oversized equipment has more refrigerant that could leak (and oversized equipment is also less efficient and more expensive). SWA works with design teams and verifies engineering calculations to limit oversizing. We’ve also monitored performance of many systems over time, and we’ve found oversizing can dramatically reduce efficiency (and certainly increase up-front costs).

Use systems with less refrigerant and fewer connections.

Large buildings with VRF systems can have miles of refrigerant lines (no exaggeration) with many, many joints. While there is limited data on this, it certainly seems that leakage will be a bigger problem here than with other system types (e.g., packaged terminal heat pumps, water-source heat pumps, etc.). SWA works with clients to design the best HVAC systems for their buildings and particular goals, and limiting refrigerant is now a topic very much on the table (along with upfront cost, efficiency, comfort, serviceability, etc.).

Changing Refrigerants

Refrigerants are changing to chemicals with lower GWP. The two most common replacements for air-source heat pumps and VRF systems are R-454B and R-32. These have GWPs of about a quarter and a third that of R-410A, respectively. Per federal regulations, if you’re installing a new residential split system with R-410A:

• the equipment must have already been manufactured or imported (before 1/1/2025)
• you need to get it installed before 1/1/2026

New VRF systems get an additional year to comply according to the EPA, but some states are implementing these restrictions more quickly (such as New York).

While these lower-GWP refrigerants will help limit the climate impacts of leakage, the refrigerant change is not an alternative to excellent installation and refrigerant management. The new refrigerants are still potent greenhouse gases, and preventing leaks is still very important. These refrigerants are also slightly flammable, and there are additional requirements for tools and installation details.

This will hopefully not be a major concern for small systems (such as in single-family homes), but bigger buildings with bigger systems may need to take additional steps such as sealing and ventilating shafts with refrigerant lines, installing leak detectors, and rigorously maintaining these systems. Check local codes for requirements on this front.

This is a dynamic topic. Regulations and equipment are changing dramatically and immediately. Reach out with questions; we’re here to help!

Contributor: Robb Aldrich, Principal Mechanical Engineer