Most every company that replaces water heaters and HVAC systems haul off the old one. Especially if it is being replaced under the Mfr's warranty as they will want the old one back most of the time. When I worked at home depot we had at least 25-30 come back a week as people would fake a leak to get them swapped out before the warranty expired. Tons of people also came along at night and would dump old appliances in our parking lot. Local scrappers were pretty good about cleaning up the parking lot by 6am.
For a few months we even had a scrapper who would chain a trailer to a lightpole way out in the lot and had a sign on it saying free appliance disposal. It worked great for him until a shady roofing contractor filled his trailer full with old shingles 2 weeks in a row. He removed the trailer after that....


We had a "white goods" hauler that would come and get all the returned appliances and the old ones that we took in when installing new ones. I dont know what they did with all of them but im assuming the white goods guys took them straight to the scrappers as they would get all pissy if there were a lot of vanity cabinets or plastic bathtubs in the load.
If there was nobody there to supervise them as they loaded the truck they would usually only take appliaces and we would have to call their company and make them come back for the non scrappable items.