Can I install used carpet that's been removed from another home?
Technically, yes you can, but in reality the results might not be great:


Carpet is measured and cut to fit a house's floorplan: individual pieces are cut from a carpet roll to fit around the tricky bits in your house (door openings, inside closets, etc.) and then taped and ironed together on site. Unless you have the exact same floorplan, you're going to have some scrap, meaning it will have to come from a bigger house so that you have enough to fit yours1.
Removing carpet without damaging it can be tricky. Think about your house's floorplan, and how you'd roll up a single piece of carpet to get it out your front door. Finding the seams between pieces is difficult because the original installers are trained to join separate pieces invisibly.
Carpet has a grain, so pieces cut lengthwise from a roll will look funny next to pieces cut crosswise.
The carpet gets a different amount of wear and tear in different parts of the house; if you have to join pieces from different rooms in the original house, they may not have worn the same. This may not be an issue if the house you're taking it from is new.
Cutting carpet is somewhat demanding. Installing carpet, even with a power kicker, is a job for the young and indestructible.
Carpet can pick up surprising amounts of dirt; be sure to have it thoroughly cleaned before installation, especially if the original owners have pets.




1. I helped someone do exactly this several years ago; the carpet and pad came from an approx. 2000 sq.ft. house and he installed it in his 1000 sq.ft. basement. The house it came from was very open-plan, with large living and family rooms and three good sized bedrooms. After cutting pieces down to size to fit his basement rooms (1 large bedroom, 1 small bedroom and a living room), he didn't have a whole lot of carpet left over.