posted 10 years ago
For the question of exactly what part(s) of the new design are causing the issues, we need more info. Is the big pipe open to the active chimney? Is it open on the bottom ?
If the big pipe is open all the way up, you are getting no draft at all to help the fire - any heat just pulls air up the big pipe. The extra elbows are also adding drag to the flue, reducing the draft. You really need to cut down the big pipe so the flue can come straight out of the wall and up, and isolate the big pipe from the actual chimney. I am assuming that the original chimney had the correct height above the rooftop for safe operation; codes vary, but 4' above the highest roof within 10' is one standard.
Chimneys do work best if in the middle of the house, but that is not the worst problem here. The assembly looks a bit slipshod and I would be concerned about connections failing in a few years.