What are reliable ways to clean hay off medium-pile carpet?
Having a cage with guinea pigs in a carpeted room means that inevitably stray stalks of hay will end up on the carpet.
Using a brush is time consuming. A vacuum cleaner either cannot pick up the hay or frequently clogs in various places, requiring lengthy disassembly and cleaning.
If you must use hay, then placing their cage home on a vinyl or suchlike mat will make it easy to brush up most of the nearby hay by hand.
For the rest of it, a good vacuum cleaner will allow setting the brushes at the most effective height, by trail & error.
But things like pine needles from a Christmas tree will weave their way into the carpet, making it impossible to vacuum them, perhaps there is an alternative to hay that is easier to pick up.
So my hack is to use something else like
fleece bedding, which can be washed regularly
more natural disposable paper (can become soggy)
adsorbant wood pellets
Guinea pigs may also eat the hay you provide for bedding.
Side note: an easy way to remove dog hairs from upholstery is with lengths of clear sticky tape dabbed across it.