carpet install

I have installed and seamed carpet a few times but always with short nap carpet in my rental houses.

I have always been told and always have made sure to run the carpet in the same way but I am putting new carpet in one of the rooms of my house that is 12'3" x 13'6. If I buy a decent quality carpet with a long nap to it do I need to seam it so that it runs the same direction?

If the answer is no then I will probably want to buy a section that is 15ft wide. If the answer is yes then I can buy a 12ft with an extra 2 feet on the end.

Let me know. The place where I am getting the carpet is having a sale tomorrow that will save me some money if I only need the 12ft.

Thanks
Jon