Hostmonster Subdomain redirected to home server IP: How to ssh into home server using subdomain

You need to go into your domain's name server, and create an A record for your subdomain that points at your home IP. If you don't have a static IP at home, then you'll need to setup a dynamic DNS. There are many Dynamic DNS providers on Google; find one you like.

The key part of your question is that you "redirected" your subdomain to point at your server at home. I assume that you used something like the HTTP refresh header. When you try to reach your home server through the redirect, this is how the flow works:

1. You send a request on port 80
2. The Hostmonster server receives the request on port 80
3. The apache server sees the redirect, and forwards to the redirect's port 80
4. Your request reaches your home router on port 80
5. Your request reaches your home server on port 80

Now here's what happens when you try to ssh into your home server:

1. You send a request on port 22
2. The Hostmonster server recieves the request on port 22
3. The Hostmonster sees that your user doesn't exist on the server; access denied

The difference is that on port 80, apache sees the redirect. On port 22, sshd doesn't know about a redirect and believes you're trying to ssh into the Hostmonster server.