A fireplace is made up of many different components, one of the most important being the chimney. If you want an efficient wood burning stove or fireplace, the chimney needs to be able to carry the smoke outside, while allowing the heat to filter inside. When talking about a chimney, the principle is actually simple. Hot air rises above cold air, which means the hot gas in the chimney would rise since it is less dense that outside air.
As the gas rises, pressure differences, or draft, is produced. The draft draws combustion air into the stove or fireplace, expelling the exhaust gas to the outside via the chimney. Typically, the hotter the gas compared to the outside air the more powerful the draft. The key is that a proper chimney would produce a small draft even when no fire is burning.
The purpose of the stove or fireplace chimney is to produce drafts, pulling combustion air into the appliance while safely exhausting gases from combustion out. Therefore, certain things must happen for this to be efficient. For instance, a chimney must be able to isolate close combustible materials from flue gas heat while also tolerating high gas temperatures that are caused by chimney fires and over-firing. Additionally, a chimney should conserve flue gas so a powerful and consistent draft is created. Then, a chimney should also resist corrosion.
For a chimney to be installed properly, it needs to be put within the house envelop opposed to simply lining up against the wall. What happens is that if the chimney were installed along the outside wall, it would be exposed to low temperatures and high winds. This cold effect on the chimney would decrease draft, causing problems with condensation. Additionally, the development of a cold back draft is possible whenever a fire is not burning, pushing cold air into the home. With this, you would likely also smell a smoky odor.
By installing the chimney within the envelop, the draft is much stronger and because the chimney is protected, your home would ultimately be more comfortable. Of course, you need to make sure that any chimney being installed follows strict building codes. This means the top of the chimney has to extend a minimum of three feet above the point where it would exit the roof.
Other requirements for code include the chimney being two feet higher than any other roof, obstacle, or building within a horizontal distance of ten feet. The purpose of strict building codes is to ensure the chimney is positioned higher to avoid problems associated with air turbulence. Finally, the chimney flue needs to be the same size as that of the flue collar. Unfortunately, if the size were too large, you would have issues with flue gas flowing faster while having less time to lose heat. Typically, hiring a professional to handle the installation of a chimney is the best way to go.