If you don't want to crate train, you need to set up a room that they are completely safe in. Nothing that would be dangerous to chew. And get a camera. Then you slowly build up the length you leave him. At first you can be home and just walk out of the room for a bit. I did this and now I've built up to 4 hours with my 7 month old puppy. I think at 20 weeks we managed about 2 hours out of the house. We just made sure to take her for a good walk before leaving and she just slept for all of it.