The federal government believes heat pumps are the future of home heating, so much so that the Inflation Reduction Act of 2022 provides a tax credit to homeowners who install a new one. Heat pumps burn no fossil fuels and consume a fraction of the energy that electric furnaces do.

But that’s not to say that heat pumps make no impact on the environment. They still do, mostly because they use refrigerant.

In the past, refrigerants for refrigerators and air conditioners have proven to have a negative effect on the environment. In 1987, an international treaty called the Montreal Protocol banned the use of refrigerants most commonly used at that time. Turns out, the chemicals these refrigerants contained were partially responsible for the depletion of the ozone layer in the earth’s atmosphere and the seasonal “ozone holes” over the North and South Poles.

The refrigerants that have come after the Montreal Protocol don’t damage the ozone layer, but they still come with some adverse environmental impacts. Consequently, the development of the perfect refrigerant is a work in progress. As of yet, no one has developed a refrigerant without some safety concerns. That shouldn’t stop anyone from installing a heat pump, though, because the benefits of the technology far outweigh the risks.

What Is a Refrigerant?

The refrigerant in an air conditioner, refrigerator or heat pump is a compound that cycles inside the refrigeration coils. The refrigerant is able to transfer heat from one place to another — in the case of a heat pump, from indoors to outdoors. No refrigeration system would work without a refrigerant.

The refrigerant used in a heat pump system must have several qualities:

• Low boiling point;
• Non-toxic;
• Non-flammable;
• High potential for heat absorption;
• Zero effect on the ozone layer; and
• Low global warming potential.

There are four common classes of refrigerants: chlorofluorocarbons (CFCs), hydrochloroflurocarbons (HCFCs), hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFOs). CFCs and HCFCs contain chlorine, which is the chemical responsible for ozone depletion, and both have been phased out or are in the process of being phased out. Most modern refrigerants are HFCs, HFOs or a combination of the two.

Is Heat Pump Refrigerant Safe?

Heat pumps manufactured before 2010 were charged with R-22 refrigerant, an HCFC that is in the process of being phased out because of its effect on the ozone layer. If you have an older heat pump system, you may — depending on the model — be able to replace the R-22 refrigerant with a safer R-410A. If you continue to use your system with R-22, you won’t be able to have it recharged after 2030, when the final stage of its phase-out goes into effect.

R-410A is an HFC that has no ozone depletion potential. It’s sold under the brand names Gentron AZ-20, Suva 410A and Puron. Heat pump systems manufactured after 2010 are already charged with R-410A. While R-410A has no effect on the ozone layer, it does have global warming potential. Because of this, it is also in the process of being phased out by the EPA.

Beginning in 2023, the refrigerant used in new air conditioning and heat pump systems is R-454B, an HFO compound. It can’t be used in systems designed for R-410A. It has low global warming potential and no ozone depletion potential, but unfortunately, it is mildly flammable.

So far, it looks like you can’t have everything in terms of safety. But the technology is rapidly evolving, and there will undoubtedly be new developments in heat pump refrigerants over the next few years.

The Evolution of Refrigerants

Back in the 1800s, when people were using iceboxes to keep food cold, German engineering professor Carl von Linde patented the first refrigeration system that relied on the expansion and contraction of a refrigerant. The one he used was ammonia, and many subsequent refrigerators also used ammonia or chemicals such as methyl chloride and sulfur dioxide. These chemicals are toxic, flammable and were responsible for many accidents.

In 1928, an engineer working for General Motors, invented a completely inert “miracle” class of compound to replace these dangerous chemicals. They were known as chlorofluorocarbons because they contained carbon, fluorine, hydrogen and chlorine. This compound was marketed by DuPont under the brand name Freon.

Freon became widely used until 1970 when James Lovelock (who is known for promoting the Gaia hypothesis) was able to detect molecules of these substances floating around in the atmosphere. Soon after, scientists detected chlorine monoxide in the stratosphere. The only way it could get there was if chlorine-rich CFCs were failing to disintegrate in the lower atmosphere and were migrating to the upper atmosphere and reacting with ozone.

That was a giant red flag, and CFCs were banned soon afterward.

As CFCs were being phased out, scientists developed a number of alternatives, including HFCs and HCFCs, but they too are deemed harmful to the environment, particularly because they are greenhouse gases, and some are mildly flammable. HFOs are the most recent development. They are formed from hydrogen, fluorine and carbon atoms, and have zero ozone depletion potential and low global warming potential. Given the possibility that HFOs may in the future be discovered to have some as yet unknown environmental drawback, there is also a movement toward using naturally occurring compounds like carbon dioxide, isobutane and propane — and once again, ammonia — as refrigerants.