I always thought that Fancy rats were slightly different than Norways. I was thinking that Norway's were only large brown sewer type rats. Getting back to my original question, I have my rats in the basement and I only get that "eww what's that smell" from my mother and sisters who don't like my snakes to begin with...haha. I clean my rats weekly and have only about a max of 70-80 rats (includes Breeders, small-med, weaned, hoppers, fuzzies and pinks) at any one time. The "smell" is really minimal most of the time and only noticable around the 6th day after I have cleaned them. My mice on the other hand seemed to stink after just a few days and I cleaned them as often or more. Oh well.