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Carrier has completed the US Department of Energy’s Cold Climate Challenge and will now begin production of cold climate residential heat pumps at its factory in Collierville, Tennessee.

The units are reported to have operated reliably at 100% capacity at 0ºF, down to -13ºF in the field and down to -23ºF in Carrier labs.

They use R454B refrigerant.
https://www.carrier.com/residential/en/us/news/news-article/carrier-completes-department-of-energy-s-cold-climate--heat-pump-challenge--transformative-innovation-set-for-2024-commercial-rollout.html