Chimney professionals all over the country recommend that any chimney flue be capped.This chimney is properly capped to avoid debris or nesting material from making the chimney a CO hazard.Caps are extremely useful in that they protect the flue system from rain that falls straight down. 
Although this is rare, rain falling with no wind, that water that falls straight down into the flue system will greatly increase creosote production. Chimney caps also prevent birds from nesting in your chimney and racoons from entering as well. They will bring in loads of extremely flammable nesting material which can cause a fire to occur in the actual flue system of your chimney as opposed to in the firebox. Even if you are not burning your fireplace these critters carry disease.
You can actually run yourself into a problem if chimney swifts enter your chimney for the season. These are federally protected birds, and if chimney swifts decide to take up residence in your chimney you will have to let them be from early spring til late summer. Chimney companies or other pest removal service can be fined per bird or egg removed from a chimney.
Standard, single flue stainless steel chimney caps are generally to install and relatively cheap. These run generally about$200, assuming your chimney flue system is near average size (approximately 12″x12″). Larger flue caps may need to be special ordered by a company and prices vary greatly. If you are purchasing a multi-flue cap and having installed by a professional it can cost you up to about $600. These multi flue caps have less of a likelihood of blowing off in wind storms because they are generally more heavy than smaller caps.
Not all caps are the same however, and generally you get what you pay for. Here at my chimney sweeping operation we always recommend stainless steel chimney caps. Whether you need a single flue cap or a multi-flue cap, stainless steel is worth the cost because it will not rust over time and is very resistant to deterioration. It is very difficult for racoons, squirrels, and other critters to chew through the stainless steel mesh that protects the chimney flue from debris and unwanted visitors. I also recommend never installing a cap which has been painted, especially painted black. These caps will rust! The rust will stain the entire top of your chimney, crown and brick alike. This stain is very difficult to remove and you often have to call in a professional to do so.
With the economy not turning around at the rate that the average consumer would prefer, people are still looking for any and all possible ways to save money and stay on top. People are cutting back in ways like we have never seen; at the grocery, at the gas stations, and summer vacations. What if there was a way to increase your savings on energy each month all year round? If you could pay between $500 and $600 dollars to keep your heated and cooled air from floating up out of the chimney, would you take advantage of the technology? When no fire is lit in the fireplace, there is no reason to have your damper open. With the damper open you are merely allowing the air that you paid to have heated or cooled to rise up and out of the chimney!
Having an old or broken damper in your chimney it is like having a window open all year round. You especially feel the effects of this air exiting the chimney in the winter months because the warm air rises up and out of the chimney. Here in Cincinnati, my service technicians recommend the installation of a Lock-Top or Lock-Top II damper. As stated previously these generally run between five and six hundred dollars installed but will enable savings year round for as long as you live in the home. For more information on chimney flue caps, check out our other article Chimney Flue Caps 101.
You can find a reputable Chimney Sweep in your area by using this link to the National Chimney Sweep Guild locator : http://www.ncsg.org/search. Also be sure and go online and read their customer reviews from Google, BBB and AngiesList. I’m never impressed with those cheaper “Swab and Rob companies