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My traditional heat pump (using R744) claims to produce about ~37dB, and while I have not measured it I can say I would not be able to hear it over a light breeze while standing right next to the thing, let alone inside the house with a wall in the way.

To be even quieter than that is remarkable, IMO.

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I'm curious, where did you get a heat pump that uses R744? As far as I know, none of the major manufacturers offer one for residential use. I'm also curious about how well it works for you.

It is super common in Japan for domestic hot water heating. It was pioneered by the government of Japan, electronic goods firms, and the power companies.

You'll see them sold under the EcoCute name. Daikin, Panasonic, and Corona (no relation) make them. They get used for homes meant to only have water and electricity hookup, called "all electric" homes.

We have this thing https://www.sanden-hot-water.com.au/specifications/ IIRC with a 300L tank. It was quite a nice upgrade from our old 1960's era 2-phase instant hot water unit that was slowly failing - cold showers in winter are not fun.

As user Danieru replied the heat pump is a a Japanese import (although the tank and rest of the system is locally made).

Same outfit in the US: https://www.eco2waterheater.com/

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