A timely post
A couple of additional thoughts. I am not sure about south of the 49th, but up here it makes sense to call a professional chimney sweep with a good reputation to clean your chimney at least once per season. Insurance companies like that a lot... and if God forbid, something happens, they can immediately rule out incorrect cleaning as a possible cause/contribution to the incident.
I generally call our local chimney sweep at the beginning of the season.. he is due here on the 14th I think, and then again after the new year when we usually have a few thaws, we call them in again to reclean and make sure that there is no creosote buildup. We also have one specific sweep that we want to clean our chimney. He has been doing it for the most part for the last 21 years with a couple of exceptions. Even though the company warrantees the work, each sweep tends to work differently with different priorities. We were not happy with a couple of replacement sweeps, and the company now only sends the one we request. It pays to build a good relationship with those whom you depend on to maintain your chimney.
Cleaning chimneys is a daunting task and many have gotten hurt whilst doing this, and many of those injuries were preventable from what the stats say. So, if there are any issues that could affect the safety aspect of chimney cleaning, please err on the side of caution and hire a professional to provide the service.
Unfortunately, along with a few other seasonal chores/projects, chimney cleaning is also the theatre of choice for many scam artists. Before you contract with anyone, research them to ensure that they are who they say they are, they have all the required credentials, and any credentialed company will gladly produce the certification simply because you ask. IF the prospective contractor balks... walk.. no RUN very fast away from them. We just had a 3 or 4 week scare with a scam artist posing as a sweep and bilking many customers in the 3 maritime provinces.. PEI, NB and NS...