In the published specs HP says regarding paper sizes for the Z3100:
All standard sizes larger than US letter
I'm not sure what this means since I tried to load a full Innova Cold Press Art 36 x 48 sheet and got an error message something like - sheet to large.
I was able to load the paper by telling the printer it was a roll. That was OK except unlike printing to a sheet the printer would only print within about 2 /78 from the bottom of the "roll" ( one wasted sheet and ink!) while it will get much closer to the end of a sheet.
I taped a small sheet of paper which reached the paper sensor switch to the sheet feeder to override the paper sensor and that seems to work.
I'm not sure what the real paper size limit is. I can't find that information anywhere yet.