Assuming there are no safety or insurance issues, I think it would depend if the heater existed when the strata plan was first registered. If it didn’t, OC permission would have been needed before it was installed. And if OC permission was not given, the OC can have the heater removed from common property. If the current lot owner installed the heater that owner would have to pay for the removal and restore the common property, else it would be an OC expense.
Even installing an air conditioner on common property needs OC permission as this VCAT decision shows: https://www.austlii.edu.au/cgi-bin/sinodisp/au/cases/vic/VCAT/2013/933.html?stem=0&synonyms=0&query=conditioner%20and%20%27owners%20corporation%20list%27