I also find no residue from my DF-50's anywhere. Granted it's a huge room but, when you only use a half pint of fluid in a year, spread out over 98,000 cubic feet, residue is non existent. I think it's fair to say if you had a DF-50, you wouldn't notice any buildup either since you'd only have to run it maybe 20- 30 seconds per evening that you're doing anything in your home.