That's weird because I have 11 pet rats in my bedroom and 2 doing QT in a tiny little room and no one coming over to my house can smell them. I have them all litter trained though and keep them on fleece that is changed every 4 days with that cat litter made from recycled newspaper in the litter boxes.
OP, they 'shouldn't' stink. They are very clean animals that groom themselves as much as cats. What they need is ventilation and enough room in their cage so they don't have to sit in their own waste and a decent diet; that should keep the smell down with weekly cleanings. They are no where near as bad as mice. If you have bp's, you may want to look into ASF's instead of normal rats. They breed much easier and are also very clean with little odor.