What is Pellet Vent chimney?

[gdeangel]

As a novice, I am confused about the different types of chimney pipes out there, and what the clearance requirements are...

so what is the difference between Class A & Class L chimney pipe, and why do you need Class L for pellet burning applications? Also, seems like Class A lets you have 2" to combustibles... is it the same for Class L?

I've also seen a few references to double wall pipe that requires greater clearances like 6" - I'm assuming that those are for use in place of single wall pipe where 18" of clearance isn't possible... and that they are completely different from double wall class A chimney pipe? Do I have this right?

Any help understanding this is appreciated. THanks

 

[Metal]

Class A (listed to 103HT) is all fuel pipe (wood, pellet, coal, gas, oil, etc.) and has a MAXIMUM clearance-to-combustibles of 2" (some have tested there's and have lower CTC's). It is usually double wall with ceramic insulation, or triple wall with air insulation.

Type L Vent is for lower heat applications such as oil, pellet, or gas appliances and usually has anywhere from 3"-1" CTC depending on manufacturer. It is double wall, but only has a very small air gap (~1.4").

Double Wall Black pipe is all fuel, but can only be used in the immediate room that the appliance is in, before breaching a wall or ceiling you must transition to Class A. It has different CTC's depending on manufacturer, but most are 8". Most have a Stainless Steel inner flue.

Single Wall Black pipe is not tested for CTC and therefore has the generic 18" rating. Most are just galvanized steel and is relatively cheap.

 

[Fsappo]

So, if you are installing a pellet stove, you use L pipe, don't look for any ways around it.

 

[gdeangel]

That really helps a lot, thanks for the information.

Just to make sure I've understood correctly, it sounds like with a pellet stove you can use Class A or Class L (Class L sounds less expensive) once you breach a wall or ceiling, and before that, it's a question of clearance whether to use single or double wall black pipe...

Where you breach the wall, even with a Class A / L with a low CTC, I would need to also be adding a thimble (?) to create a gap between the pipe and the combustible wall material. Are there different thimbles manufactured for the particular CTC of a certain pipe (e.g., if your using a 1" CTC Class A, is there a thinner thimble than if you have a 2" CTC Class A?)

Thanks!