It is very unlikely that a residential storage heater has asbestos if built within the last 30 years. Asbestos was usually hand-applied in-place; fiberglass or rock-wool was easier to install at the factory as a sheet. A card of asbestos was used on really old water heaters near the electrical connections, but that was replaced with other material decades ago. Old oil water heaters may have had asbestos in fire chamber materials, but the asbestos lawsuits have been going on for twenty years now and such materials were hazardous for manufacturer's survival, so they have eliminated the use.
The most likely possibility of asbestos use was in the insulation pipe wrapping used at commercial installations; rarely in homes after 25 years ago. I am sure the manufacturer of the particular storage tanks would tell you the last time they used asbestos.
It is good to check - for compliance - , but most unlikely.