Trying to figure out what kind of piping you need to install your fireplace, stove, or any other hearth appliance can be an intimidating task. In an effort to simplify things for you, we will look at several aspects of the most common types of chimney pipe and explain their uses and applications.
What we have here is a guide to help you, the consumer, become a bit more familiar with chimney pipe. First and foremost, in any installation, you'll want to begin by consulting the owner's manual for your hearth appliance. Different fireplaces and stoves have varying venting requirements. These requirements involve more than just the kind of pipe you need; it also includes specific information regarding clearances and offsets that must be followed for safe and proper installation. If anything in your manual is unclear or confusing, contact the manufacturer of your appliance directly for clarification.
But, if you need further assistance or simply can't get a hold of your manufacturer, feel free to give us a call at 1-800-203-1642 or email us at firstname.lastname@example.org. Our NFI certified specialists will be happy to assist you in any way that they can.
What is Class A Chimney Pipe?
Class A chimney pipe has many names, often referred to as double-wall chimney pipe, triple-wall chimney pipe, all-fuel pipe, or insulated chimney pipe. Class A pipe is used to vent high-temperature exhaust released from wood, coal, and oil-burning appliances such as fireplaces, stoves, boilers, and furnaces.
Not every venting system requires a Class A pipe, but it is absolutely necessary for use with all wood-burning fireplaces and stoves.
Class A chimney pipe is UL-listed, which permits its use with a range of different vent pipe manufactured by other fabricators and an even wider variety of fireplaces, stoves, inserts, and furnaces. However, it is important to note that you should never mix-and-match different brands of Class A chimney pipe within one chimney system unless specifically allowed by the manufacturer. The different brands of pipe are all distinctly engineered and must be used as a complete system from beginning to end.
If you are looking to extend or redesign your current chimney system, you need to know the make and model of your existing Class A pipe and purchase the same type, if possible. Unfortunately, if your existing make and model of pipe is a discontinued or obsolete brand, you will likely need to rebuild your chimney system from scratch. Building codes prohibit the use of any adapters not approved by the manufacturer. These adapters are very rare and are usually only offered by a manufacturer to link a very similar discontinued piping system to a currently offered system.
There are two types of Class A chimney pipe:
- Solid-packed chimney — These pipes have smaller inner diameters (usually ranging from 5 inches to 8 inches) that have some insulation, either double-wall (like Simpson DuraVent DuraTech pipe) or triple-wall (like Simpson DuraVent DuraPlus pipe). These pipes contain fiberglass or ceramic insulation to stay cooler on the outside and must maintain a 2-inch clearance to combustibles.
- Air-cooled chimney — These pipes have larger inner diameters (usually ranging from 8 inches to 24 inches) with no insulation. An example of this kind of Class A pipe is the IHP chimney pipe that is required for use with Superior and Astria manufactured fireplaces. As the name implies, these pipes rely on the air circulating within them to keep the outer wall cooler and must also maintain a 1 or 2-inch clearance to combustibles.
When using Class A chimney pipe, it is important to plan or route the vent run wisely to minimize costs and maximize your savings. Class A pipe is usually manufactured with either a stainless steel or galvanized (or galvalume) outer wall. When running Class A pipe within a masonry chimney, a chase, an attic, or any enclosure inside the home, it is economically wise to use galvanized pipe. It is highly recommended, if possible, to install your chimney in the interior of your home. Having your chimney system exposed to the outdoors brings with it the risk of a "cold hearth syndrome," which can hinder drafting and produce more creosote.
The need for stainless steel only arises when your pipe will be exposed to the elements. If the galvanized pipe is exposed, it is susceptible to eventual rust and corrosion. This is especially true in coastal areas. If you must use galvanized pipe outside, we urge you to paint your pipe with a high temperature, rust-resistant paint. Just remember, galvanized piping must be cleaned and prepped prior to painting to remove any residual machine oil or dust from the manufacturing process.
What is Direct Vent Pipe?
Direct-vent pipe is made specifically for a direct vent gas appliance. The term "direct-vent" refers to an appliance that uses only outside air for combustion and vents all exhaust directly back outside. The appliance itself is sealed off from the room by a glass door that should never be opened while the unit is in use.
Direct-vent units are among the most popular with consumers because of their efficiency and ease of installation compared to traditional wood-burning applications.
There are two types of direct vent piping systems:
- Coaxial pipe — Consisting of a pipe-within-a-pipe configuration, a coaxial system utilizes a smaller inner pipe that is fixed inside a larger outer pipe. The inner pipe, separated from the outer pipe by spacers, vents and removes all combustion by-products and exhaust out of the appliance and out of the home. The space between the two pipes brings in fresh air from outside into the appliance for combustion. Coaxial pipe may be rigid or flexible.
- Colinear pipe — This is a system with two separate pipes, one for combustion air and the other for exhaust. These kinds of pipes are usually flexible and typically use existing masonry structures to run the piping.
Clearances for direct vent pipe may vary, and these clearances will be specified by the manufacturer of your direct-vent appliance. The general rule-of-thumb, however, is a 1-inch clearance all the way around for vertical vent runs. And if running the pipe horizontally, it must maintain a 3-inch clearance for the top half of the pipe and a 1-inch clearance for the bottom half of the pipe.
Direct vent chimney systems are specialized. Every component, including pipe, elbows, firestops, roof supports, termination caps, and etc. is specifically made for venting a direct-vent appliance. You will never convert direct vent pipe to Class A chimney pipe, and you will never convert a stove pipe to a direct vent pipe. In some circumstances, it is possible to utilize specialized adaptors to convert Class A chimney pipe into a direct vent system.
Unlike stove pipe, the use of roof supports and thimbles with direct vent systems do not serve as a conversion point to attach Class A chimney pipe. These components are only used to pass direct vent pipe safely through a ceiling or a wall. The owner's manual of every direct vent fireplace, stove, or insert will specify which brands of direct vent pipe are approved for use with that unit.
A unique and convenient aspect of direct vent chimney systems is the ability to vent and terminate in various ways. A direct vent system can be terminated either horizontally or vertically, and in some cases, it may only take a few inches of pipe directly out the back of a direct vent appliance to the outside of your home. Be sure to follow your manufacturer's guidelines for maximum horizontal run, vertical rise, etc. when designing your direct vent chimney system. The specifications for venting for each appliance will be spelled out in your owner's manual.
Direct vent units may be referred to as "top vent," "rear vent," or "slant-back." These titles refer to the position of the flue collar on the appliance. "Top vent" and "rear vent" are self-explanatory, and "slant-back" refers to an appliance with a flue collar coming out of the unit at a 45-degree angle, with easy adaptability for vertical or horizontal venting with the use of a 45-degree elbow.
Many direct vent appliance manufacturers will offer specific horizontal or vertical venting kits for particular units. When looking into purchasing these kits, be sure to find out how much pipe you would be getting and if that would be enough to complete your system.
What is Stove Pipe?
Stove pipe, also called a chimney connector, is not the same as a Class A chimney pipe, although these two are often confused with each other. Stove pipe is used for venting wood burning stoves and is only for use inside the home, or more specifically, inside the room where the stove is installed. Once the venting reaches 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 — you must also account for proper clearances from combustibles. For example, a 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 clearance from the ceiling and 6 inches from a wall. Once these clearances are met, you must convert your stove pipe to Class A chimney pipe for proper venting of your stove.
Many stove owners from years past may be surprised to know that stove pipe is never permitted to go through a ceiling or a wall, no matter how much clearance you can create. Therefore, it is never safe to use only stove pipe for venting. This is simply a matter of the way these pipes are engineered.
If used outside, stove pipe will be unable to maintain high flue temperatures, causing potential creosote buildup and increased risk of a chimney fire. Class A chimney pipe requires only two inches of clearance to combustibles because it is made to handle the highest temperatures for exhaust. This is why you must convert from stove pipe to class A chimney pipe when venting your wood burning stove.
How To Install Stove Pipe Into Chimney
There are a couple of different ways to make the conversion from a wood stove pipe to a chimney pipe for proper venting. These include through-the-ceiling or through-the-wall venting methods. Each installation calls for different components, depending on the transition point between the stove pipe and Class A chimney pipe.
Through-the-ceiling — For venting systems that run vertically through a ceiling, you must have a ceiling support box or round ceiling support piece to use as your transition point from the stove pipe to the Class A chimney pipe. The stove pipe will connect to the bottom, and the 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 round ceiling support). From here, chimney pipe will pass through a pitched roof by use of roof flashing, or it can be built into a framed wooden chase, which must be topped off with a fabricated chase top flashing.
Through-the-wall — 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, run into the 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 six inches (for connecting to double-wall stove pipe) or 18 inches (for connecting to single-wall stove pipe).
Most wood burning stoves are top-vent models, 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 vertical rise from the top of the stove (not including the flue collar itself or any elbows) before connecting a 90-degree elbow piece to turn toward the wall.
Some older wood burning stoves are rear vent models. These models require the use of a tee for cleanout purposes at the flue collar. Like top-vent models, they require a minimum of 12 inches of vertical rise before directing the vent pipe horizontally. Please see your owner's manual for more details.
There is one main difference between wood-burning and direct-vent stoves. Some direct-vent stoves are rear-vent models and able to vent horizontally from the flue collar to the wall. 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 to use a 90-degree elbow. For more information on venting direct-vent stoves, please see the section on direct-vent pipe.
What is Type B Gas Pipe?
Type B gas pipe, also called "B-Vent" or "Natural Vent," is prefabricated, double-wall metal pipe used to vent gas appliances listed for use with Type B gas vent. Type B pipe is becoming less prevalent for venting hearth products, but many furnaces and water heaters still use it.
The biggest reason for the declining use of Type B vent pipes for hearth products is their lack of efficiency, especially compared to direct vent and vent-free units. However, there is still a market for B-Vent piping for fireplaces because of its economic viability, which makes it particularly appealing for contractors and builders. Another advantage of Type B is that it is not typically susceptible to excessive draft problems, due in part to the draft hood that draws in excess air to moderate strong draft. Most B-Vent pipe has a one-inch clearance to combustibles.
Type B pipe is never suitable to be used with wood-burning or coal-burning appliances. Also, it should never be used as a free-standing exhaust pipe for high-temperature venting.
What is Pellet Vent Pipe?
Pellet vent pipe is used to vent pellet-burning or corn-burning stoves. These pipes are smaller in diameter than any other vent pipe, usually with a diameter of 3 or 4 inches. Double wall pellet pipe requires a 1-inch clearance to combustibles. And unlike stove pipe, pellet vent pipe does not require Class A chimney pipe for installation.
In other words, you are not required to convert pellet vent pipe to Class A chimney pipe when passing through a wall or a ceiling. Pellet pipe is used all the way from the pellet-burning or corn-burning appliance to the termination point.
Similar to direct-vent systems, pellet venting can be terminated either vertically or horizontally. If terminating horizontally, the cap must be at least 6 inches from the outer wall of your home. If terminating vertically, the cap must be at least 12 inches above the roof.
If you are venting for a pellet-burning insert, however, your appliance will require a flex pipe to bypass the smoke shelf. At this point you would be able to convert to rigid chimney or pellet vent pipe with an adaptor.
Types of Chimney Termination Caps
Class A Chimney Caps
Class A chimney pipes have their own specialized caps that fit right on top of the pipe at the point of termination above the roofline, commonly referred to as chimney caps. When terminating a Class A system, you must follow what is known as the "10-3-2" rule or the "10-foot, 2-foot" rule.
This rule is explained by the Natural Fire Protection Association (NFPA) as follows:
"A chimney for residential-type or low-heat gas utilization equipment appliances shall extend at least 3 ft (0.9 m) above the highest point where it passes through a roof of a building and at least 2 ft (0.6 m) higher than any portion of a building within a horizontal distance of 10 ft (3 m)" (NFPA ANSI Z223.1, Section 10.5.2.1).
Please note that this code must be met with the 10-foot radius, clear of any obstruction at the top of your pipe before your cap is installed. This rule is in place to ensure proper draft for your unit. If you have any questions about whether your system meets code with regard to this requirement, feel free to call or email us, and we will be happy to help.
Direct Vent and Pellet Vent Termination Caps
- Vertical Termination Caps: A vertical termination cap is for use, obviously, when terminating vent pipes vertically through a roof. Depending on which manufacturer of pipe you use, there may be some specialization options like a high-wind cap (to protect against wind), a low-profile cap (to protect against rain), or an extended vertical cap (to protect against extremely cold climates). And depending on your roof's pitch, you may need anywhere from 1 to 5 feet of pipe extending past your roofline. As always, check your manufacturer's guidelines for proper venting and termination of your unit. Some direct-vent caps are made of aluminum while others are made of stainless steel, which is preferable for longevity and reliability.
- Horizontal Termination Caps: One distinct difference with direct-vent systems is the option to terminate horizontally on an outside wall. As with the vertical caps, there may be a few specialized options, including round or square caps. Be sure to check your manufacturer's guidelines for proper clearances for horizontal termination of your unit. These guidelines will specify the appropriate distance you'll need from your wall, windows, doors and other parts of the home. Also, some appliances may call for a minimum amount of vent rise before horizontal termination is permitted.
- Snorkel: Patented by Simpson DuraVent, this component is for horizontal, through-the-wall terminations when a vertical rise is required to meet minimum height requirements. The most common use of this term would be installations in basements and situations where your appliance is installed below grade.
Type B Caps
Type B systems can involve a multitude of distinct piping components, and the termination point is no different. B-Vent systems can only be terminated vertically, with several different kinds of caps available depending on your manufacturer's guidelines and requirements. See the chart below for help with measurements.
Other Components for Chimney Pipe Installation
In addition to your pipe and chimney/termination cap, here are several chimney components you may need for your installation.
- Anchor Pate/Flue Adaptor: The vast majority of fireplaces, stoves, and inserts need an anchor plate (usually for zero clearance and masonry fireplaces) or a flue adaptor (usually for stoves and direct vent fireplaces) to use a particular kind of chimney system. For example, if you purchase a zero clearance wood-burning fireplace with an 8" flue and want to use the Simpson DuraVent DuraTech chimney pipe, you would need to use the DuraVent DVL 6-Inch Double-Wall Stovepipe to Stove Flue Adaptor.
- Elbow/Elbow Kit: Elbows are often needed in chimney systems for a variety of reasons. Unless you are able to vent your chimney system vertically or horizontally without any obstructions blocking your path, you are going to need an elbow of some kind. All manufacturers specify the offset parameters for each hearth appliance in the owner's manual. So you'll want to consult your manual for this specific information regarding your unit.
While many stove pipe and direct vent pipe systems use 90-degree and 45-degree elbows, Class A chimney pipe systems do not allow for more than a 30-degree elbow. In fact, you'll need two elbows if offsetting Class A chimney pipe — an elbow to start the offset and another one to end the offset. For this reason, most Class A chimney manufacturers only sell elbows in kits that have two elbows and an elbow strap for support. Also, only a limited amount of offset is permitted (usually no more than just over 3 feet or less) between the two elbows. Using the two elbows to offset Class A chimney pipes optimizes your chimney's performance and protects against drafting and flow problems.
When dealing with offsets with stove pipe and direct vent pipe, you can offset to go around an obstruction for up to nearly 60 inches for stove pipe and nearly 40 inches for the direct vent pipe. Pellet Vent pipe, however, can be offset for almost 80 inches. These are approximations. Please consult the section pertaining to offsets in the owner's manual for your appliance and the pipe manufacturer's guidelines for offset allowance with each type of pipe.
- Elbow Strap/Wall Strap: Many manufacturers provide elbow straps for many kinds of pipe to support chimney systems with offsets. You'll use wall straps — one every 4-5 feet of vent rise — when running a Class A or direct vent chimney pipes vertically inside a chase or alongside a wall.
- Ceiling Support Box/Thimble: These components are necessary for use when the pipe is exposed and exiting the room where the appliance is located. If you are venting vertically through the ceiling/roof, you will need a ceiling support box or a round ceiling support. If you are venting horizontally through the wall, you will need a thimble. In stove pipe systems, these components will serve not only as support pieces but also as the transition point from stove pipe to Class A chimney. In direct-vent systems, these will be used only for support, as there is no transition to another kind of pipe.
- Firestop/Attic Insulation Shield: When passing through a ceiling, floor, or attic, you will need to use one of these components. If a ceiling support is not used, the firestop is required for passing through ceilings in multi-story homes, while the attic insulation shield is required when passing through an attic. Both of these pieces ensure your pipe maintains proper clearances as it passes through combustible ceilings and floors.
- Chimney Tee/Tee Support: When your chimney system passes through the wall, you will need a tee and tee support to serve as a 90-degree bend to turn your chimney up toward your roof. Tees are most commonly used as connectors between stove pipe and Class A chimney systems, as the pipe that exits the home needs to be turned 90-degrees to run vertically up to the roof for termination. All Class A chimney tees will need tee support as the base support point for the vertical pipe.
- Roof Support: Placed underneath the flashing on the roof, the roof support is designed to support pipe both above and below the roof. There is a limited amount of pipe it will support, particularly below the roof, but this component is ideal if you do not have a ceiling support box as part of your system.
- Flashing/Storm Collar: A flashing and storm collar go hand-in-hand; they are designed to protect your chimney system from weather damage. The flashing is the piece that covers the hole in your roof where the pipe penetrates. The storm collar fits around your pipe just above the flashing to prevent rain or snow from getting into the minuscule crevice between your flashing and pipe. You need to select a flashing appropriate for your roof pitch. A roof pitch is a measurement of vertical rise over a horizontal distance of 12 inches. For example, if your roof has a vertical rise of 3 inches over a 12-inch horizontal distance, your pitch is 3/12.
- Extended Roof Bracket: When your chimney extends more than 5 feet above your roof, you need an extended roof bracket to provide stabilization for your pipe against the wind.
We hope this guide has been helpful and informative. Remember, it cannot be stressed enough to consult your owner's manual above all else when considering how to vent your hearth appliance. Some local codes require you to use only the kind of pipe listed in your owner's manual for your unit. Always check with your local building code officials when designing a chimney system to ensure proper installation. If you have lost your owner's manual, please call or email us, and a member from our knowledgeable staff will be happy to see if we can locate one for your fireplace, stove, or insert.