optimal air purifier usage

hi y'all. my roommate does not take very many covid precautions, so i recently got an air purifier for the living room. since she comes in and out, i'm not really sure what the best system is for having it on. its not feasible to have it going all the time since i don't want to go through the filters that quickly, and especially since the electric bills have been so high this winter. does anyone have thoughts or suggestions? much appreciated!