Not that old, plus I don’t see it.

Asbestos is great at insulating really hot things so was used on boilers , especially ships and industrial to insulate the hot pipes and improve efficiency. However in this case we need something with thermal mass: any sand or rock might do, or water, or oil, or a modern phase change material. That material next to the heater will get hot but the entire mass won’t, so can be insulated with standard materials. There’s no point in something like asbestos

An important part of my point was also that what I assume were cheap materials was enough to take advantage of nightly time of use metering. In upstate NY, a standard “radiator” per room was sufficient, similar to hot water or steam heat