There are kits you can get that are pretty inexpensive. Since you don't burn "real" wood, you'd think your chimney would be cleaner, but that's not necessarily the case. It's kinda like your stove: needs to get hot and stay hot to burn off the creosote and other materials that the burning fuel leave behind. And firelogs generally don't get that hot. If it's been more than 2 or 3 years since you've cleaned your chimney, get a pro to do it. Once it's cleaned, get a good chimney cleaning kit and clean it in the spring and again in the fall. Note: chimney cleaning is really dirty work, so be prepared to look sooty (remember chimney sweeps?)