posted 10 years ago
For an 8-inch system size, start with your 50-ft, subtract the length of piping, as you have. But then each elbow subtracts 5-feet from that original 50; that's minus 10-feet for a 180-degree turn (two 90-degree elbows).
Your vertical rise not only does not count against you (sorry for all the negatives! heheh) some folks calculate it adds, but I don't recall about that really. Try finding some of Ernie Wisner's posts, where he talks about this. He rattles these rules of thumb right off the top of his head, he's done it so often.
But really, I think you are good with either layout.
With regard to the chimney, the point to be taken (other than fire safety, and construction details in making the through-ways) is to get the proper height. Best is a minimum of 2-feet higher than your highest roof ridge; reasonable, and for most areas I've seen, also by code, is to find the highest roof line, or other substantial object, within a 10-foot radius of your chimney, and make the chimney height a minimum of 2-feet taller; in other words, the top opening of the chimney ought to be at least two feet taller than anything within 10 feet of it.
And put a rain cap on too. You can get directional one's for like $50, or you can make a low pressure one out of three T's, forming an H-like shape. All of this assumes you do not have something unusual, or a giant tree blocking all the wind there, or something strange going on in the vicinity of your proposed chimney. If you have any doubts, pay a chimney sweep or other fireplace/chimney expert to look at your site.