Capital Gains Tax (Sale of Primary Residence)

I recently sold my primary residence and realized a net profit of
more that 250K (I'm single).I'll now be buying a house for about
the same $ that I got for my previous house.

In order to avoid the cap gains tax,does this house have to be my
"primary residence" and is there a minimum period of time that I must
own it before selling?

Thanks much!