I'm not sure why you would rent one when you could just buy one for $50.
The Wagner Power Steamer 715 is ideal for the quick and effective removal of all types of wallpaper in small and medium jobs. The 1 gal. tank has a 1500-Watt heating element that provides up to 70 minutes
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Zinsser 32 oz. DIF ultra-power concentrate wallpaper stripper is our fastest, most concentrated wall covering remover. After using this economical product, wallpaper will be ready to remove in 2 to 5 minutes. Powerful concentrate and superior performance and easy to apply by sprayer, roller, or...
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But there are many ways to remove wallpaper besides the steamer, the spray can also work along with just hot water. Time wise it depends on the wallpaper and how many layers of wallpaper is on the walls, sometimes there are 3-4 layers and that will take longer. At one point I think I figured out that it took me about 2 hours per wall in an average bedroom so about 8 hours or more per room. Probably a little bit more because there's clean up afterwards and sometimes you need to go back and clean up little bits that you missed.