Every carpet cleaner should use a door drape for EVERY job. Keeps cold, heat, bugs.... in and out. Unless you want to be regarded as a hack to your customers you need a door drape.
Honestly I didn't know there were guys out there that didn't use them.
If you are interested in an easy to use drape, check out the Bane door guard.
Here is a pic. It isn't one of those goofy ones with the foam, it is simply material that covers the openings. It doesn't keep the door from opening, so you have to put a jug or something up against it to keep it shut.
Say NO to being a hack.