Pellet Stove Pipe & Venting

We'll cover common types of pellet stove venting materials and venting configurations in this article. eFireplaceStore wants you to have the smoothest hearth installation possible. And, we are always here to help with our NFI Certified Technicians.

PL or Type-L Vent Piping

This is dual-wall pellet vent piping without the ability to feed combustion air to the stove. At first glance, these pipes appear to be nearly the same as the Type B gas vent pipe. They feature the same twist-lock style ends. They have a 5/8" inner versus outer wall size difference and a 1" clearance requirement to combustible materials. They also have a galvanized steel outer pipe, although PL/L piping is usually available in both unpainted or black painted. While they do share some characteristics, these pipes have some fundamental differences.

Type PL or L pipe trades the aluminum inner wall of B-vent for a stainless steel inner wall. In most cases, PL or L inner walls are made of 444 stainless steel or similar. The use of this material ensures longevity against the mildly corrosive effects of pellet fuel flue gases.

Type PL or L piping is available in 3" or 4" versions. When selecting this type of venting, ensure it meets UL641 standards. To achieve this rating, the venting system is tested to meet a sustained temperature of 570 degrees and a flash temperature of 1,700 degrees. This procedure ensures flame containment during a thermal chimney event. A thermal chimney event, in case you're wondering, is exactly what you think it might be, a chimney fire.

It is also important to know whether your appliance calls for vent piping that uses sealed seams. That is to say, pipe joints that will not leak flue gases from positive combustion pressure.

Unlike B-Vent, Type L venting routes in a variety of ways. This gives you more creative freedom to place your vent termination. This is due to the fact that the vent pipe is under pressure from the combustion air fan within the pellet stove. The fan forces flue gases through the system, allowing for either vertical or horizontal discharge.

If you're looking to vent your pellet stove vertically, the vent pipe is routed much like a wood stove. An adapter is attached to the appliance. It is used to route the vent system up through the ceiling/roof using a ceiling support box, attic insulation shield, and flashing kit.

Almost all pellet stoves use a 3" vent collar, so in many cases, 3" Type L vent pipe should be used. But, sometimes the manufacturer requires a 4" vent pipe for longer vent runs. In this situation, an adapter is usually installed at the vent collar on the stove versus later in the vent run. This helps cut down on the amount of air friction, which can restrict airflow.

L-Vent Configurations

There are five ways to vent an L-vent pipe system across horizontal and vertical vent runs. We'll cover each here, from easiest to most complex, with a few advantages and disadvantages of each.

Completely Horizontal Run — This vent run consists of an L-Vent run that routes from the rear vent collar on the stove. The pipe will need to go a short distance. It will route from the stove directly through an outside wall. And then, it terminates using a purpose-made horizontal vent cap.

For this type of run, you'll need an appliance adapter, the correct length of the vent pipe, a wall thimble, and a horizontal vent cap.

The low installation cost and low profile of the termination make this a good choice for many homeowners. This is ideal for those who use the appliance sparingly or who rarely have power outages.

A major disadvantage of this type of run is that the vent run can only be cleaned by removing the exterior termination. And because of its proximity to the ground, the termination cap is prone to damage. Additionally, if power is lost while the unit is in operation, smoke will back up into the appliance.

Combination Run — Somewhat like the horizontal run, this type of vent run begins at the back of the unit. Unlike a complete horizontal run, this type of run includes at least one length of the vertical run. You could attach an elbow or a tee from the back of the stove and route the vent pipe up the interior wall before exiting horizontally and terminating. Or, you could route the vent pipe through an adjacent wall before going vertical along the exterior wall and terminating.

You'll need the same components listed for a horizontal run. Plus, you'll need any tees or elbows and wall brackets required to maintain the vertical portions.

The advantages of this type of pipe run are that it's easier to clean and harder to damage by accident. This is because the termination is higher up from the ground. Additionally, if there is a power outage, a natural draft will ensure that smoke continues to vent.

Do take into consideration the higher cost of this type of vent run. It also has the potential for an unappealing appearance of the vent pipe, since it will be more visible on the interior or exterior of the home, depending on routing.

Vertical Run — A complete vertical run is much the same as a freestanding wood stove. Except, larger offsets are usually allowed due to the positive pressure venting system. This type of vent run is required for stoves installed on interior walls. It is also needed for situations where exterior obstacles or structures prevent a horizontal run.

The usual appliance adapter, any tees or elbows, and lengths of pipe are required. But, you'll also need ceiling supports, an attic insulation shield, a storm collar, and a vertical vent cap.

This is a good choice for several reasons. First, it is easier to clean. It routes exhaust gases further away from the home. And, it produces a stronger draft for the fire during a power outage.

Of course, more materials mean higher cost and a more complex installation. Additionally, more vent pipe is usually visible in the home, which may or may not be to your design tastes.

Vertical Run with a Masonry Chimney — A less common type of vertical run is where a pellet stove uses an existing masonry chimney. It requires a clay flue and a clay or metal thimble that connect the vent pipe of the pellet stove to the chimney.

This system usually works by positioning the pellet stove directly in front of the chimney. It uses a short length of pipe to align venting with the chimney. Then, it includes a tee or elbow to turn the pipe before routing the piping through the chimney thimble. You'll finish this type of system by installing rigid vertical sections within the chimney. Or, you can use a flex adapter and flexible stainless steel venting up the chimney.

You'll need the appliance adapter, any tees/elbows, lengths of pipe, a flex adapter or flex trim collar, and some flex venting.

This an appealing choice for those wishing to upgrade from a wood-burning masonry fireplace to a pellet stove. It is relatively low cost and allows you to use your existing masonry chimney. On the flip side, the interior chimney access is a bit restricted, making any work on the chimney difficult to do.

Vertical Run with Prefabricated Chimney — Like provisions of a masonry chimney, some L-vent systems can use an existing prefabricated chimney system. You can do this if you have a system from a previously vented wood stove or fireplace. All you need is a special adapter and flex vent to route flue gases through this existing chimney.

You'll still need the appliance adapter, any tees/elbows, pipe, chimney adapter, and flex venting. But, the savings may be worth it. There is one possible downside, though. The transition from the new to the old may be difficult to make aesthetically pleasing. Also, note that any offsets in the original venting may make routing the new venting challenging.

Combustion Air Intake with PL/L Vent

There are several ways to bring in combustion air for a pellet stove while using PL or L Vent piping. Since PL/L vent piping doesn't suction air in through it, there are a few options for external air supply.

Most pellet stoves have a combustion air intake collar adjacent to the flue collar. It is about two to three inches in diameter. Most designs allow for combustion air to be drawn from the room without modification to the air intake collar. To limit the amount of air drawn from the home, it is highly recommended to supply a dedicated source of combustion air to the stove from outside the home. Doing this maximizes the unit's efficiency. Some of these options are detailed below.

You can use a dedicated 2" or 3" pipe that passes through the outside wall, separate from the exhaust vent. This system will need an independent vent cap. Generic aluminum flex venting or galvanized steel ducting can be used for this purpose.

Another option is a combustion air run that combines at the wall thimble and passes through the same thimble as the exhaust vent. This run terminates into a dual-purpose cap or right below the main vent cap.

You could also bring in the air through a purpose-built manifold. Some brands of PL/L vent offer a combustion air manifold that combines with the flue vent. The manifold passes both intake and exhaust through the wall.

Finally, you could use a vertical air system through an existing chimney. No matter if it's prefabricated or masonry, you could run a second flex line for the intake. It sits adjacent to the flue system and has a specially designed vertical vent cap.

Direct Vent Piping

A less common but very convenient option to standard Type PL or L venting is a product such as Selkirk's Direct Temp venting system for pellet stoves. This high-quality, co-axial direct vent pipe series adapts vent piping for use with pellet venting.

It does this by taking the Direct Temp pipe and adding special adapters to combine the exhaust flow and intake air into a single pipe system. A small flexible vent pipe runs from the intake air collar of the stove and connects it to the outer wall of the direct vent pipe. Then, the stove flue collar is attached with a separate adapter to the inner wall of the direct vent pipe. Once combined, this allows for a single direct vent pipe system to pass through the wall to the outdoors.

This is possible due to the materials in use in the product line. Most brands of direct vent pipe feature an aluminum inner wall. This material is adequate for gas-burning installations since the flue gases are non-corrosive. But, it is inadequate to support flue gases expelled from a pellet stove. Instead, Direct Temp features a 304 stainless steel inner vent wall with sealed pipe joints. This material allows it to handle combustion gases from a pellet appliance. It also ensures the byproducts will not leak when under pressure.

Direct-Vent Installation Configurations

Direct Vent pellet systems offer three primary configurations. Each is an excellent choice depending on your needs. We'll detail these configurations below, with the parts, advantages, and disadvantages of each.

Completely Horizontal Run — This configuration routes from a rear vent and air intake collar on the pellet stove. It has a short distance of horizontal flow through an outside wall. It then terminates using a purpose-made horizontal vent cap.

For this, you'll need several components. First, you'll need an adaptor to combine the intake and exhaust into the single coaxial pipe. You'll also need vent collars, the correct amount of Direct Temp pipe, an exterior adaptor, a wall thimble, and the specialty cap.

This type of configuration features the lowest cost and easy installation. So, it's easy to see why homeowners choose it. However, there are a few things that may create some hesitation in this choice. The direct-temp pipe is higher than PL/L pipe, and there is some risk of damage to the termination cap. Plus, the adaptors are not very pretty to look at if aesthetics is a concern.

Combination Run — Like a horizontal run, this configuration exits straight outside the exterior wall. The vent pipe uses an adapter from the back of the stove. It routes the pipe up along the interior wall before exiting horizontally and terminating.

Along with the components needed for a complete horizontal run, you will need at least one 90-degree elbow to turn the pipe vertical.

The addition of a vertical section of the pipe does allow for the stove to draft in a power outage. And, the higher vent termination avoids most accidental damage to the vent cap. The higher cost of this system and the less visually appealing vertical runs may be considered disadvantages.

Vertical Run — Just like with the PL/L venting, a complete vertical run is much the same as a freestanding wood stove. Again, there are larger offsets allowed, thanks to the positive pressure venting system.

You'll need an adaptor to combine the intake and exhaust into the coaxial system. You will also need the vent collars, the correct lengths of Direct Temp piping, an exterior adaptor, ceiling supports, attic insulation shields, roof flashing, and a chimney cap.

This type of configuration runs the vent gases up and away from the home. It allows the system to have the best possible draft in the absence of power. Additionally, it is the easiest to clean from the bottom up.

It has the potential to have the most labor-intensive installation. Of course, it depends on access to the routing path. But, this often means that it is the most costly of the pellet venting systems. However, for a centrally located pellet stove, this is the most viable venting choice.

Industry's Finest

Simpson Duravent —Offering a broad range of high quality venting systems, the Duravent line of PelletVent Pro and PelletVent for multi-fuel systems are no exception to this history of quality. A broad range of adapters and components in both 3 and 4-inch diameters ensures that every installation can be accommodated with no hassle.

Selkirk —Offering a proprietary direct vent system for venting pellet stoves has placed Selkirk among the more innovative in the field of pellet venting products. Selkirk Direct-Temp pipe is used with these systems to ensure maximum combustion air efficiency and versatile termination options.

Olympia —The Ventis line of pellet vent pipe by Olympia chimney boasts consistently high pipe to pipe quality and ease of installation, as well as a full line of adapters and components in both 3 and 4-inch size ranges.

Installation Notes

No matter which venting you choose, there are some installation considerations to remember.

You will want to follow all manufacturer's instructions on securing each pipe section. This prevents the pipes from coming apart by accident.

Use appliance adapter or adaptation tees as needed. To ensure a tight seal at the appliance, it is necessary to use the proper components. Appliance adapter collars or appliance adapter tees have a tapered collar. The tapered design creates a tight seal at the start of the venting system.

You will need to follow manufacturer standards for the design of your venting route. Each manufacturer will specify a maximum horizontal run, vertical run, and offset allowances. They will also identify prohibited configurations. Lastly, the manufacturer will specify which brands and size of pipe you can use with the appliance. It is important to abide by all guidelines to ensure the pellet stove will vent as designed. Improper venting can lead to a build-up of fly ash in the system, stove overheating, or stove shutdown.

Ensure that there are no air leaks from the venting system during the test burn. This can be done by using a smoke stick around all seams. If the smoke blows away from any of the seams, you will need to seal an air leak.

And, make sure to double or triple check the clearances for any holes you must cut in your home's structure. Not only will this ensure safety, but it will also prevent the build-up of fly ash.

Maintenance for your Pellet Venting

Now that you've installed your pellet stove and have all your venting in place, it's time to consider the upkeep of the system. It's important to keep a close eye on all pellet venting systems since most are under positive pressure when operating.

Pellet vent systems are designed to be airtight, but a lack of sealant, gaskets, or improperly assembled pipe sections can create leaks. Not only does this mean that exhaust fumes are going into your home but fly ash as well.

Fly ash is a unique occurrence to pellet fuel due to the dry and lightweight nature of the fuel. The combustion fan that supplies oxygen to the burn pot can also cause lightweight ash to rise into the venting system over time. Although many models feature an ash trap to capture most of the ash, some ash will inevitably escape.

Fly ash can be a good visual clue that there is a problem. This is because fly ash will collect on the outer surface of the vent pipe at and around the location of the leak. After using your pellet stove for a couple of weeks, you'll want to inspect the pipe joints for evidence of fly ash residue.

With the venting system is inspected and in good order, you can expect that the appliance will operate as designed.

Regular Inspection of Pellet Venting

To be sure that your pellet stove stays in top working order, it's important to understand the unique requirements of a pellet venting system.

Of course, you're going to have the stove itself inspected every burn-season, but you probably don't think about inspecting the venting. While maintaining the stove itself, you should follow the manufacturer's instructions. Your unique venting presents a different challenge as far as maintenance and cleaning.

You should inspect your pellet venting systems on a weekly basis during the regular operation of the stove. Once you have an idea of how ash builds up in your vent pipes, you can make adjustments to the inspection period. Each venting system is different and ash will build up in tees, elbows, and terminations before straight runs.

It's important to make sure that the design of your vent system has regularly accessible cleaning points. This means that you'll want to make sure that you've included places you can get into the vent piping from. For example, when redirecting a horizontal pipe run to a vertical direction, like from a rear venting stove, you should use a tee with a cleanout cover in place of a 90-degree elbow. Be sure to install a termination cap that is appropriate for the installation and readily accessible for cleaning.

Cleaning a venting system that has bends or sharper angles will need a flexible brush system. This Rutland Pellet Stove Vent Brush will allow for a more thorough sweep of the system, removing all ash and debris build-up.

For completely horizontal runs, you can use a traditional fiberglass rod system. But, you will need the same type of poly brush head as the flexible system. You shouldn't use metal brushes as they can damage the venting system.

Lastly, it is important to get a purpose-built ash vacuum to collect all loose fly ash. Standard vacuums and shop vacuums will not work, as their filtration systems will quickly clog or will allow fine ash to flow back into the room. Systems such as this Ash Vacuum by US Stove are specially designed to handle ash that still has some warmth to it.

Shipping

Individual suppliers will usually only ship up to three venting components via parcel. If more than three, the suppliers will normally choose to bundle the components onto a pallet. This helps protect the individual components from damage during the shipping process. The components are strapped and plastic wrapped to prevent shifting. The suppliers also stack the components vertically as much as possible. This enables the components to be set back from the edge of the pallet to reduce the risk of damage further.

You will still want to inspect any and all pieces when you receive them. It is important to make sure that no piece is too damaged for use in your installation.

Summary

In conclusion, you have several options for venting your new pellet stove. These choices vary based on your budget, your climate, or your aesthetic preferences.

At eFireplaceStore, we want you to have the best vent system that you possibly can. If you have questions or concerns, always feel free to reach out to our NFI Certified Technicians.

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