Trying to figureout what kind of piping you need to install your fireplace, stove, or any otherhearth appliance can be an intimidating task. In an effort to simplify thingsfor you, we will look at several aspects of the most common types of chimneypipe and explain their uses and applications.
What we have hereis a guide to help you, the consumer, become a bit more familiar with chimneypipe. First and foremost, in any installation, the owner's manual for yourhearth appliance should be consulted. Different fireplaces and stoves havevarying venting requirements. These requirements involve more than just thekind of pipe you need, it also includes specific information regardingclearances and offsets that must be followed for safe and proper installation.If anything in your manual is unclear or confusing, you should contact themanufacturer of your appliance directly.
Class A Chimney Pipe
Class A chimney pipe has many names; it can also be referred toas double-wall chimney pipe, triple-wall chimney pipe, all-fuel pipe, orinsulated chimney pipe. Class A pipe is used to vent high-temperature exhaustfrom burning many common fuels such as wood, coal, and oil. Basic exampleswould include fireplaces, stoves, boilers, and oil-burning furnaces. Not everyventing system will require the use of Class A pipe, but it is absolutelynecessary for use with all wood-burning fireplaces and stoves.
Class A chimneypipe is usually UL-listed, which permits various manufacturers' pipe to be usedwith an even wider variety of manufacturers' fireplaces, stoves, inserts, andfurnaces. However, it is important to note that you should never mix-and-matchdifferent brands of class A chimney pipe within one chimney system. Thedifferent brands of pipe are all distinctly engineered and must be used as acomplete system from beginning to end. If you are needing to extend or redesignyour current chimney system, you need to determine the make and model of yourclass A pipe and purchase that same type if at all possible. Building codesprohibit the use of any adapters to link different chimney brands. In a chimneysystem where you are converting stove pipe to class A pipe (see the Stove Pipesection for more details), you may reconfigure your stove pipe system apartfrom your class A system and vice versa.
There are two types of class A chimneypipe:
- Solid-packed chimney. These pipes have smaller inner diameters (usually ranging from 5 inches to 8 inches) that have some insulation, either double-wall or triple-wall. These pipes use fiberglass or ceramic insulation to stay cooler on the outside and have a 2 inch clearance to combustibles.
- Air-cooled chimney. These pipes have larger inner diameters (usually ranging from 8 inches to 24 inches) that have no insulation. An example of this kind of class A pipe is the FMI chimney pipe that is required for use with FMI and Vantage Hearth manufactured fireplaces. As the name implies, these pipes rely on the air circulating within them to keep the outer wall cooler and also have a 2 inch clearance to combustibles.
Class A pipe is usually manufactured witheither a stainless steel outer wall or a galvanized (or galvalume) outer wall.When running class A pipe especially when you have your system outside, it is undoubtedlywise to use 304 stainless steel pipe instead of 430 or galvanized steel. Havingyour system outside brings with it the risk of a cold chimney, which wouldhinder drafting and produce more creosote. If galvanized pipe is exposed, it issusceptible to rust and corrosion that will eventually ruin it if leftunprotected. On the contrast, 304 stainless steel gives your system outstandinganti-corrosion ability.
If you must use galvanized pipe outside,it is strongly recommended that you paint your pipe with a high temperature,rust-resistant paint. Galvanized piping must be cleaned and prepped, prior topainting.
Stove pipe, also called chimney connector,is not the same as class A chimney pipe, though the two are often confused witheach other. Stovepipe is used forventing wood-burning stoves and is only for use inside the home, or, morespecifically, inside the room where the stove is installed. Once the ventingreaches the wall or ceiling, it must be converted to class A chimney pipe.Depending on which kind of stove pipe you use--single-wall or double-wall--youmust also account for proper clearances from combustibles. For example,single-wall stove pipe requires 18 inches of clearance from ceilings or walls.Double-wall stove pipe, on the other hand, requires only 8 inches of clearancefrom a ceiling and 6 inches from a wall. Once these clearances are met, youmust convert your stove pipe to class A chimney pipe for proper venting of yourstove.
Many stove owners from years past may besurprised to know that stove pipe is never permitted to go through a ceiling ora wall, no matter how much clearance you can create. Therefore, it is neversafe to use only stove pipe for venting. This is simply a matter of the waythese pipes are engineered. If used outside, stove pipe will be unable tomaintain high flue temperatures, causing potential creosote buildup andincreased risk of chimney fire. Class A chimney pipe requires only 2 inches ofclearance to combustibles because it is made to handle the highest temperaturesfor exhaust. This is why you must convert from stove pipe to class A chimneypipe when venting your wood-burning stove.
There are a couple of different ways tomake the conversion from stove pipe to chimney pipe:
- For venting systems that run vertically through a ceiling, you must have a ceiling support box or round ceiling support piece that will be your transition point from stove pipe to class A chimney pipe. The stove pipe will connect to the bottom and class A chimney pipe will attach to the other side, either running through the ceiling support box itself or an attic insulation shield (in the case of a round ceiling support).
- For venting systems that run horizontally through a wall, you must have a thimble. A thimble is designed to allow Class A chimney pipe to pass through the wall to run into room where your appliance is installed, and then connect to the stove pipe. Depending on what kind of stove pipe you use, the class A chimney pipe must come into the room 6 inches (for connecting to double-wall stove pipe) or 18 inches (for connecting to single-wall stove pipe).
Most wood-burning stoves are top-ventmodels, meaning the flue collar will be on top of the unit. For any horizontal,through-the-wall venting system, you must have at least 12 inches of verticalrise from the top of the stove (not including the flue collar itself or anyelbows) before connecting a 90-degree elbow piece to turn toward the wall. Someolder wood-burning stoves are rear vent models. These models require the use ofa tee for cleanout purposes at the flue collar. Like top-vent models, theyrequire a minimum of 12 inches of vertical rise before directing the vent pipehorizontally. Please see your owner's manual for more details. This is one maindifference between wood-burning and direct-vent stoves. Some direct-vent stovesare rear-vent models and are able to vent horizontally from the flue collar tothe wall. Some other direct-vent stoves are "slant-back" models,meaning the flue collar is positioned at a 45-degree angle on the unit,allowing some versatility for vertical or horizontal venting without having touse a 90-degree elbow. For more information on venting direct-vent stoves,please see our section on direct-vent pipe.
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