Overview of Chimney Pipes
To get started, what are chimney pipes? How many types are there, and which one is best for your hearth appliance? This section will answer each of these questions in depth to ensure you have all the information. For images of the various chimney pipes, feel free to click the links throughout this article.
Chimney pipes provide the ventilation system needed for your fireplace or wood stove. These appliances may sit within a masonry clad enclosure or inside a chase enclosure.
The chimney pipe promotes venting efficiency. It contains the heat emitted through the flue pipe from coming into contact with combustibles. Surfaces like walls, ceilings, attics, and roofs tend to degrade and dry out over time. The chimney pipe provides much-needed protection.
6 Common Types of Vent Pipes
At this point, you might be wondering how many different types of chimney pipes there are and how to tell them from other venting products. You may even want to know the advantages and disadvantages of them, too. We'll cover the answers to these common questions. But first, it is necessary to clarify the term chimney pipe. It is often overused to reference all types of ventilation pipes. But, it actually refers to the Class A chimney pipe used for wood-burning applications.
To be clear, there are six main types of vent pipes:
- Class-A Chimney Pipe
- Pellet Vent Pipe
- Gas Vent Pipe
- Type-B Vent Pipe
- Direct-Vent pipe
While each variety of vent pipe is somewhat similar in overall construction and appearance, Class-A chimney is specifically built for wood burning applications and certain models of multi-fuel hearth appliances. This section provides a basic overview of each type of chimney pipe system. It distinguishes the purpose of many pipes by their names.
Class-A Chimney Pipe - As stated, Class-A chimney pipes ventilate wood-burning or retrofitted gas-log fireplaces. They are also used to complete the venting of a wood stove and facilitate the transition of stove pipe to chimney pipe. Every product that is used in a Class-A venting system should be listed to meet UL103 guidelines, the rating the ensures a safe standard for chimney systems.
Stovepipes ventilate a wood-burning stove while pellet pipes ventilate pellet-fueled stoves. Gas vent pipes and Type-B vent pipes are for gas fireplaces only.
You may hear retailers refer to direct vent pipes as coaxial pipes. This is because they come manufactured with a small pipe fitting within a larger pipe. For these, customers can choose between flexible or rigid installations. But, coaxial direct vent pipes are unique to direct-vent fireplaces. Pellet, B-vent, and direct vent pipes should never be utilized to vent an appliance specifically rated for use with Class-A chimney.
Class-A chimney pipes are often available as air-cooled chimney systems. And, please know that they are not right for everyone. While more affordable than insulated varieties, they are used mostly with open-faced fireplaces. They're also versatile. You can use them with wood-burning units or retrofitted gas logs. Almost all air-cooled chimney systems are proprietary, meaning they are purpose built by the manufacturer of the fireplace, for that specific fireplace. Depending on the type of fireplace being considered, the purchase of an air-cooled chimney system may be a requirement.
How is the Class-A Chimney Pipe Rated for Safety? - Most manufacturers of the air-insulated chimney use two rating systems for safety. The first is the Underwriters Laboratories (UL) 103 standard. To ensure compliance, UL rates standard chimney systems up to 1,700°F (927°C). The chimneys must demonstrate continuous operation at a 1,000°F (538°C) flue output. This includes a 10-minute test at 1,700°F (927°C).
Most areas in the U.S. accept this standard rating. The higher rating is UL-103HT. It follows the same 1,000°F standard operating temperature. But, it requires the chimney to also endure three 10-minute chimney events at 2,100°F (1149°C).
These systems are usually made out of thicker and higher grade steel. This allows them to handle hotter temperatures without damage, such are warping or kinking. Some areas of the U.S. require the use of UL-103HT Class-A chimneys, but they are the standard for homes in Canada.
How Does a Class-A Chimney System Work? - Class A systems operate using a 2-wall or 3-wall pipe system. This depends on the regulatory codes in your area. The chimney is composed of an inner pipe, an optional middle pipe, and an outer pipe. The inner pipe encases heat emitted from the fireplace. It carries potentially toxic combustion particles outside the home to atmosphere.
Think of it this way. Fire creates buoyancy by heating the air in the fireplace. As heated air rises, it carries combustion particulates up the chimney. Also, during the burn, the fireplace creates negative pressure in the home. This happens as it removes air to create a flow of draft up the chimney.
Unfortunately, much of the heat for open faced fireplaces is lost during this ventilation process. And, heat loss reduces heating efficiency, which can raise the cost of your electric or gas bill.
The space between the inner and outer walls for a 2-wall system functions as an air jacket. It insulates the chimney pipe and keeps the surface of the outer wall from becoming too hot. This works in a similar way for the 3-wall venting system. The space between the middle wall and the outer wall serves the same insulation purpose. So, how is the insulation air supplied?
This is an excellent question. The air-cooled chimney uses a specific vent cap and a special attachment collar located on the fireplace. The cap is located at the top of the chimney system and functions as both an air baffle and protects against pests and precipitation entering the venting system. Through the baffle, it allows constant air to flow through the spaces between the pipe walls. In other words, the vent cap supplies the air that creates the air jacket insulation.
It can be easy to confuse the air used to insulate the chimney pipe with the air used for combustion. All combustion air for a Class-A chimney comes from the room where the fireplace is installed or via a combustion air kit made for the fireplace.
As such, the outer pipe functions much like a shield for the inner pipe. It protects combustible surfaces from drying out and igniting from radiant heat. Clearance spacers or springs ensure the pipes maintain the recommended space between each other. This space is usually set at two inches for two main reasons.
First, this space allows air to dissipate the heat around the inside pipe. As discussed earlier, this serves as a natural cooling agent to reduce radiant heat. Second, it prevents the outer pipe from absorbing heat emitted from the inner pipe. But, there are problems with this type of ventilation system worth noting.
The main problem with air insulated chimneys lies in their reliance on outside air for insulation. It is common for these ventilation systems to perform poorly in very cold climates. This is especially true where there are extremely windy and cold winters.
Why should outside temperatures matter if you're burning your fireplace inside the home? Here's why. Large differences in outer and inner wall temperatures can create "cold hearth syndrome." This is where the fireplace has difficulty starting due to the very cold air.
Cold air is denser than warm air. So, extreme temperature differentials can create a dense air pocket in the chimney. The drastic difference in temperatures prevents lighter, warm fireplace flue gases from penetrating. This problem amplifies for exposed parts of the chimney above the roof. These areas tend to have improper enclosures and insulation.
What does this mean for you? You've likely figured it out already, but since those gases can't go up and out of the home, they have to go somewhere. This means they're more likely to come back down into your home and pollute your breathing air.
Even if the chimney flue gases are able to penetrate the denser cold air, the extreme temperature difference between the walls of the chimney will lead to increased levels of condensation on the inner pipe walls. This condensation has a tendency to capture flue byproducts, drying them into creosote. Rapid creosote buildup can lead to poor chimney performance, unwanted odors, and in extreme cases, chimney fires.
Should you decide to install this type of chimney, take note of your winter temperatures. Also, consider the direction prevailing winds blow. If you see temperatures at or below zero, consider using an appliance that can utilize an insulated chimney system.
3-Wall Chimney Systems
Reaching their prominence in the 1970s, 3-wall chimney systems are still available today but are not as common. They were used in highly populated areas to reduce potential house fires from spreading. But, they are still used in many areas of the United States today. The third wall provides an extra layer of safety for extreme temperatures.
Like the 2-wall pipes, the 3-wall system includes a space between the inner pipe and the outer pipe. This space supports air circulation. It uses 1" to 3" spacers to maintain the required clearances between each pipe. It is important to note, however, that there are two different types of 3-wall systems.
There is a traditional air insulated version, which has three separate, free-floating walls held together by a vent cap. This version is composed of three pipes. The inner pipe is made of stainless steel and is usually the exact same pipe used in 2 wall varieties. The middle pipe, made from galvanized steel, surrounds the inner pipe. The third outer pipe allows air flow as a natural cooling agent. It surrounds the inner and middle pipe as a barrier. So, it protects against contact with combustible surfaces.
The second type of 3-wall venting system combines elements from the air-cooled and insulated chimney systems. The first two walls are fused together with a thin layer of insulation between them. The insulation is only approximately .25" thick. The third wall provides an open space for air-cooling. This version of piping can be an alternative for homes in colder climates, as it provides an extra layer of air space between the flue and outdoor temperatures. Many manufacturers of proprietary chimney systems will offer both a double and triple walled air cooled chimney system to fit the same fireplace, with a special adapter used if triple wall is chosen.
Your chimney pipe selection depends on personal preferences, compatibility, budget, and climate. As you may have realized, each system has its advantages and disadvantages.
Based on quality and durability, we deem the solid pack chimney system most efficient. This claim may be a bit controversial for regions still relying on the 3-wall venting system. But, technological advances in the industry makes the solid pack chimney equally efficient. It should be noted that only high efficiency wood burning stoves and fireplaces can use a solid pack or fully insulated chimney system.
When You Should Choose a Solid-Pack Chimney System
If you see temperatures at or below zero, consider using a solid insulated chimney system and related fireplace or stove. This type of chimney works well at containing the heat from flue gasses. And, it also works well in colder climates where the outer wall of the pipe may be exposed.
New EPA regulations hold wood appliances to higher standards. But, sealed high efficiency wood burning appliances will be with us for some time to come. Eventually, they will become the norm, with open wood burning appliances fading from prevalence. The efficiency of front-sealed units and their environmentally-friendly combustion makes them more attractive.
How the Air-Cooled System and the Insulated System Differ
Most manufacturers specify a type of air-insulated chimney to use. And, most of the time, it's their own brand. But, solid-pack chimney systems are often constructed by 3rd-party companies. This means they are tested or rated for use with appliances made from various brands. This gives you more options to find the best and most cost-effective system. In some cases, a single high efficiency wood burning appliance may be rated to accept over half a dozen different solid pack chimney lines.
Solid-pack systems are a step up in cost from air insulated chimney systems. But, they are usually smaller in diameter and made from higher quality materials. In almost all cases this ventilation system is required with wood stoves or high efficiency fireplaces, but there are a few exceptions. That's because these hearths reach much higher temperatures and as a result, need the added protection to prevent too much heat escaping from the chimney as radiant heat.
Closed-combustion fireplaces and wood stoves or sealed hearth appliances use gasketed doors. Such doors prevent dilution air, otherwise known as room air, from entering them during normal operation. Sealed appliances utilize approximately 5-15% of the overall air volume that an open-faced appliance uses. This means they have very little air to cool, or dilute, higher flue gas temperatures. But, high temperatures must be controlled.
These chimney sections come constructed as single units. They have built-in insulation between a fused inner and outer wall. They differ most from air-cooled systems in their availability of stainless steel on the outer wall of the pipe, but these systems offer you variants. You can choose between galvanized steel, painted galvanized steel, or stainless steel for the outer walls.
It is also common for installers to switch back and forth between these materials for different sections of the chimney. For instance, an installer may use galvanized steel inside a wall or an attic. But, he may switch to stainless steel for sections exposed to the outdoors. This is because exposed sections need better corrosion resistance, while cost can be saved by using galvanized sections within the home.
The inner wall of the most chimney systems will be stainless steel. But, solid-insulated systems will usually use 304-grade stainless steel. This is better quality than the 430-grade stainless steel seen in most air-cooled systems. The material quality for each chimney system accounts for flue temperature differences. You'll see higher flue temperatures in sealed units and with its increased heat resistance, 304-grade stainless steel can handle temperatures that would cause a lesser grade to warp or buckle.
Insulated chimneys usually rely on a 1-inch thick blanket of insulation. It keeps the outer wall cool and prevents framing members in the home from drying out. The insulation material consists of ceramic wool, mineral wool, or vermiculite cloth. These insulation types are much denser than the fiberglass or foam insulation used in the wall or ceiling cavities of your home, allowing the much thinner layering between pipes. Since you know some material differences, it's time to learn about common regulations.
Common Regulations Installers Should Know
The most important thing to remember is to follow your manufacturer guidelines. Most installation and operation guides will identify ventilation restrictions. To learn more about the codes in your area, please visit the International Code Council's website.
Ventilation Routes - When organizing your venting design, you must consider the dimensions of a chimney. Remember, the average chimney will have a rough frame of two square feet. This excludes external cladding, veneer, or other materials. Manufacturers provide clearance requirements, in inches, from combustible material.
Clearances are provided for the appliance and chimney system. These clearance requirements will often determine the paths available to you. So, take these specifications into account before deciding on a ventilation system.
Two typical options include routing through the interior of the home via an enclosure or along an outside wall through a chimney chase. To clarify, enclosures are often referred to as a chimney chase, but they are distinctly different things. The chimney chase is secured to an exterior wall of the home. And, it typically runs the entire length of the chimney pipe. But, some builders neglect to encase the entire chimney pipe. This is especially true for the piping above the roof that is exposed to the elements.
An enclosure is simply an interior structure that is built around the chimney pipe to hide it from view. This can be a simple drywall column or similar structure. In some cases, the vent pipe may even be able to be routed through the corner of a closet or similar space where it is less noticeable.
Why You Should Consider a Chimney Chase - It's true; this type of structural frame requires more materials and extra costs. But, the benefits are worth every penny. It gives customers greater use of floor space. This is because the chase encloses the chimney and venting pipes along the exterior of the home. It prevents pipes from being seen from the exterior of the home, which can boost your home's resale value.
Certified installers will verify the framing dimensions needed to house a fireplace. They often enlarge chase dimensions to complement the exterior aesthetics of your home. In fact, you will likely prefer the chase enclosure over masonry chimneys for a few reasons. These reasons boil down to construction, materials, and labor costs.
Beyond costs, chimney chase enclosures have many design advantages as well. You have more customization options with a chase than with a bulky masonry chimney. Some interior options include shelving, recessed bookshelves, television enclosures, and top-level tapering. These designs make the unit more appealing and add significant appeal to the home.
When venting a wood stove chimney through an outside wall and along the side of your home, a chimney chase can also be used. While the chase does not necessarily have to start at ground level, it is generally the most aesthetically pleasing to do so.