Be careful which SS chimney you go with. I have seen folks on here post about chimney woes. Personally, I will be purchasing a Ventis Chimney. They use 316L stainless, while other brands use 400 and 304 which will not last long. Duravent and metal bestos use the aforementioned, so I will not be using them. Someone had a ventis system on here, and it was many years later and the chimney was still in excellent shape. The chimney might be more expensive, but it is worth it as it will last.
Like the others have said, also price out a masonry chimney. Too.