Should I ask my roommate to turn off his space heater when he leaves?

My brother has been staying with me for quite a while. He pays one third of the rent (nothing else) . Every time I put a package on his bed, his space heater is on even when he’s gone for the weekend. The dte is already 200+ a month and isn’t that a fire hazard? Should I tell him to turn it off or is that kinda rude