I got it installed in 4 rooms, 2 upstairs and 2 downstairs.... 4 grills in total but I believe its good for at least 6 outlets as air pressure is very high and we run it on 40-60% speed
didn't want to break inside walls for duct passage, otherwise could easily install 2 more grills in inner area of the house
there is a damper in grill, like we have in car ac vent, you can reduce air flow or even completely close it for specific grill....
keep in mind, I think its not gonna work in high humidity but its a very good investment....