Chimney Pipe Buying Guide

Figuring out what kind of piping you need to install your fireplace, stove, or other hearth appliance can be intimidating. To simplify things, we will examine several aspects of the most common types of chimney pipe and explain their uses and applications.

We plan to help you familiarize yourself with chimney and stove pipe. First and foremost, in any installation, you'll want to consult 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, like the DuraVent chimney pipe; they also include specific information regarding clearances and offsets that require following 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 reaching your manufacturer, please call us at 800.203.1642. Our NFI-certified specialists will be happy to help you in any way they can.

What is Class A Chimney Pipe?

Class A chimney pipe has many names, including double-wall, triple-wall, all-fuel, and insulated chimney pipe. It vents high-temperature exhaust 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 various vent pipes manufactured by other fabricators and an even wider variety of fireplaces, stoves, inserts, and furnaces. However, it is important to note that you should only mix and match different Class A chimney pipe brands within one chimney system if specifically allowed by the manufacturer. The different pipe brands are all distinctly engineered and must be used as a complete system from beginning to end.

If you want 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. Unfortunately, if your existing pipe make and model 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 rare and are usually only offered by a manufacturer to link a 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) and some insulation, either double-wall (like Simpson DuraVent DuraTech pipe) or triple-wall (like Simpson DuraVent DuraPlus pipe). They contain fiberglass or ceramic insulation to stay cooler 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) and no insulation. An example of this Class A pipe is the IHP chimney pipe 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 one or 2-inch clearance to combustibles.

Planning or routing the vent run is important when using Class A chimney pipe to minimize costs and maximize savings. Class A pipe typically has 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 a galvanized pipe. We recommend installing your chimney in the interior of your home. Having your chimney system exposed to the outdoors brings 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 is exposed to the elements. If the galvanized pipe is exposed, it is susceptible to eventual rust and corrosion, especially in coastal areas. If you must use galvanized pipe outside, we urge you to paint it with a high-temperature, rust-resistant paint. Galvanized piping must be cleaned and prepped before painting to remove any residual machine oil or dust from manufacturing.

What is Direct Vent Pipe?

Direct-vent pipe is made specifically for direct-vent gas appliances. A direct-vent appliance uses only outside air for combustion and vents all exhaust directly back outside. The appliance is sealed off from the room by a glass door, which 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 — In a pipe-within-a-pipe configuration, a coaxial system utilizes a smaller inner pipe fixed inside a larger outer pipe. Spacers and vents separate the inner pipe from the outer pipe, which removes all combustion by-products and exhaust from the appliance and home. The space between the two pipes brings fresh air from outside into the appliance for combustion. Coaxial pipe may be rigid or flexible..





coaxial vent piping

• Colinear pipe — This system has two separate pipes, one for combustion air and the other for exhaust. These pipes are usually flexible and use existing masonry structures to run the piping.

Direct vent pipes' clearance may vary, and your direct vent appliance manufacturer will specify these clearances. The general rule of thumb, however, is a 1-inch clearance all the way around for vertical vent runs. If the pipe is run horizontally, it must maintain a 3-inch clearance for the top half and a 1-inch clearance for the bottom half.

Direct-vent chimney systems are specialized. Every component, including pipe, elbows, firestops, roof supports, termination caps, etc., is specifically made for venting a direct-vent appliance. You will never convert a direct-vent pipe to a Class A chimney pipe or a stove pipe to a direct-vent pipe. In some circumstances, it is possible to utilize specialized adaptors to convert a Class A chimney pipe into a direct-vent system.

Unlike stovepipes, roof supports and thimbles used with direct vent systems do not serve as a conversion point to attach Class A chimney pipes. These components 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 terminate either horizontally or vertically. Sometimes, it may only take a few inches of pipe directly out the back of a direct vent appliance to the outside of your home. When designing your direct vent chimney system, follow your manufacturer's guidelines for maximum horizontal run, vertical rise, etc. The specifications for venting for each appliance are listed in your owner's manual.

Direct vent units are also known 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, easily adaptable for vertical or horizontal venting with the use of a 45-degree elbow.

Many direct-vent appliance manufacturers offer specific horizontal or vertical venting kits for particular units. When considering purchasing these kits, find out how much pipe you need and whether 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 previous stove owners may be surprised to learn that stove pipes are never permitted to go through a ceiling or a wall, no matter how much clearance you can create. Therefore, using only a stove pipe for venting is never safe. This is simply a matter of the way these pipes are engineered.

If used outside, stove pipes cannot maintain high flue temperatures, causing potential creosote buildup and an increased risk of a chimney fire. Class A chimney pipes, on the other hand, require only two inches of clearance to combustibles due to handling the highest exhaust temperatures. 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 several ways to convert a wood stove pipe to a chimney pipe for proper venting, including through-the-ceiling or through-the-wall venting methods. Each installation requires different components depending on the transition point between the stove and Class A chimney pipes.

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, running through the ceiling support box or an attic insulation shield (in the case of round ceiling support). From here, the chimney pipe will pass through a pitched roof using 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 —Venting systems that run horizontally through a wall require a thimble. A thimble allows 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 a tee at the flue collar for cleanout purposes. 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. Many manufacturers recommend Duravent stove pipe

There is one main difference between wood-burning and direct-vent stoves. Some direct-vent stoves are rear-vent models that can 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 using a 90-degree elbow. For more information on venting direct-vent stoves, please see the section on direct-vent pipes.

What is Type B Gas Pipe?

Type B gas pipe, also called "B-Vent" or "Natural Vent," is a prefabricated, double-wall metal pipe used to vent gas appliances listed for use with Type B gas vents. Although Type B pipe is becoming less prevalent for venting hearth products, 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 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, partly due to the draft hood that draws in excess air to moderate a strong draft. Most B-vent pipe has a one-inch clearance to combustibles.

Type B pipe is never suitable for use with wood-burning or coal-burning appliances. It should also never be 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. Usually three or 4-inch in diameter, these pipes are smaller in diameter than any other vent pipe. A double-wall pellet pipe requires a 1-inch clearance for combustibles. 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.

Like direct-vent systems, pellet venting can be terminated vertically or horizontally. If terminating horizontally, the cap must be at least 6 inches from the outer wall of your home. The cap must be at least 12 inches above the roof if terminating vertically.

However, if you are venting for a pellet-burning insert, your appliance will require a flex pipe to bypass the smoke shelf. At this point, you can convert to a rigid chimney or pellet vent pipe with an adaptor. DuraVent pellet stove pipe is one of the most common brands.

Types of Chimney Termination Caps

Class A Chimney Caps

Class A chimney pipes have specialized caps that fit right on top of the pipe at the point of termination above the roofline, commonly called chimney caps. When terminating a Class A system, you must follow the "10-3-2" or "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 building's roof 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 within the 10-foot radius and clear of any obstruction at the top of your pipe before your cap is installed. This rule ensures a proper draft for your unit. If you have any questions about whether your system meets your local code regarding this requirement, please call or email us; we will gladly help..

Direct Vent and Pellet Vent Termination Caps

• Vertical Termination Caps: A vertical termination cap is used 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). Depending on your roof's pitch, you may need 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 specify the distance needed from your walls, windows, doors, and other home parts. Also, some appliances may call for a minimum 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 is in basements and situations where your appliance is installed below grade.

Type B Caps

Type B systems can involve many piping components, including the termination point. B-Vent systems can only be terminated vertically, and several caps are 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, you may need several chimney components 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 DuraTech All-Fuel Chimney Pipe Masonry and Zero-Clearance Fireplace Anchor Plate. Similarly, if you purchase a wood burning stove with a 6" flue and want to use Simpson DuraVent DVL double-wall stove pipe, you would need the DuraVent DVL 6-Inch Double-Wall Stovepipe to Stove Flue Adaptor.


• Elbow/Elbow Kit: Elbows are often needed in chimney systems for various reasons. Unless you can vent your chimney system vertically or horizontally without obstructions blocking your path, you need an elbow. 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 with 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 pipes optimizes your chimney's performance and protects against drafting and flow problems.

When dealing with offsets with stove and direct vent pipes, you can offset to go around an obstruction for up to nearly 60 inches for stove pipe and nearly 40 inches for direct vent pipe. Pellet Vent pipe, however, can be offset for almost 80 inches. These are approximations. Please consult the section about 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 pipes 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 as support pieces and 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 must use one of these components. If 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. These pieces ensure your pipe maintains proper clearance 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. It will support a limited amount of pipe, 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 that is appropriate for your roof pitch. A roof pitch measures 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 stabilize your pipe against the wind.

Summary

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 flue 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 need help with your owner's manual, please call or email us, and a member of our knowledgeable staff will be happy to see if we can locate one for your fireplace, stove, or insert.