I always start off with the Shared cM Project. I prefer it over sites that give you percentages of probability.
1722 cM is enormous and you and this man are very closely related.
- Half sibling is a strong possibility. The range is 1317-2312 with an average of 1783, almost exactly your actual match of 1722 cM.
- Uncle/nephew is equally strong. The range is 1349-2175 with an average of 1750. Half uncle is out of range though. He would be the full sibling of one of your parents, or the son of one of your full siblings.
- Great uncle/nephew is also possible. The range is 251-2108 with an average of 914. In this case, he would be the full sibling of one of your grandparents, or the grandson of one of your full siblings.
- Grandparent has a range of 1156-2311 with an average of 1766. This could be the case if one of your parents had a bio dad different from the dad that raised them (or they were adopted, etc). Or if you have a child with a son you don't know about.
That's it. One of the above things is true.
I hope your match writes you back. He may be overwhelmed with finally being so close to figuring out his birth family, or this could be a surprise to him too. Or he might not be seeing his Ancestry messages (I've missed some even though I'm signed up for email notifications). Finding out at least his age will narrow things down. Please update when you get more information.