Cleanouts are key for long term maintenance. Any flue run needs to have an opening where you can stick a flue brush/shop vac hose into to clean even if it isn't that often. I only need to open mine up and clean every other year unless I burn less than ideal wood
(I only had to do that once to learn that lesson). I thought one of my runs would be accessible from one end (it has some twists and turns) and when it came time to clean I found out that I really need another cleanout so now I have to add one after the fact which is a pain. So, if you have any u-bends to do, make them H's with two tees and you have cleanouts or figure out what it takes. Breakup is kind of starting I guess (it is melting a bit in the latter part of the day these days but we still have feets of snow!). Yes, what an awesome winter!