The NEC lets you do almost anything up to 30 volts and doesn't regulate what's inside the appliances you plug into your outlets, just the wiring that's part of the building.
I thought it was up to 48 volts, but it looks like NFPA 70 Article 725 Class 1 circuits are only up to 30 volts, and there's a power limitation I didn't know about: only 1000 VA. So you can only run a pretty small storage heater from a Class 1 circuit, and even Class 1 circuits have some safety requirements: https://www.ecmweb.com/cee-news-magazine-archive/article/208...
Class 2 and Class 3 also require the use of a listed power supply.
I thought it was up to 48 volts, but it looks like NFPA 70 Article 725 Class 1 circuits are only up to 30 volts, and there's a power limitation I didn't know about: only 1000 VA. So you can only run a pretty small storage heater from a Class 1 circuit, and even Class 1 circuits have some safety requirements: https://www.ecmweb.com/cee-news-magazine-archive/article/208...
Class 2 and Class 3 also require the use of a listed power supply.