Put the carrots, celery, onions, garlic, farro or barley(if using) in the slow cooker and lay the chicken on top.
Add 8 cups of water plus the remaining ingredients except the noodles, and cook on low for 6 – 10 hours or on high for 3 – 4 hours.
Leave the slow cooker on and transfer the chicken to a colander placed inside of a large bowl to catch extra juices and let it cool (if you don’t have time to let it cool, you can work with very clean rubber gloves instead).
Meanwhile, add the uncooked noodles to the slow cooker and let them cook for 20 - 30 minutes or until the noodles are done (See Tip below for how to keep your noodles firm).
Remove and discard the skin and bones from the chicken and shred the chicken meat with your fingers.
Return 2 1/2 cups of the chicken to the soup, and reserve and refrigerate or freeze the rest of the chicken for another use.
Serve it immediately, refrigerate it for up to 3 days, or freeze it for up to 3 months.