After learning the rules the hard way during my own install, I have spent a lot of time answering posts on here asking the question that I should have asked - Do I need to insulate my liner?
For folks who may still be asking the question, here is what I have learned:
Question # 1 - Do I need a Code Compliant Chimney?
Most folks ask "Do I really need to insulate my liner?" The question could be better phrased "Do I really need a Code Compliant Chimney?" If you believe you do need your chimney to meet code, keep reading. Many masonry chimneys don't meet building code requirements, as they were not built with the required one or two inch external air gap to combustibles that is required for wood fired appliances. I say one or two inch air gap because the gap required depends on many things, like whether you are in Canada or the USA, or whether the chimney is on an outside wall of the building or not.
This air gap keeps the heat that can occur during a chimney fire (2100*F flue gas temp) from damaging surrounding combustibles. In most cases, like when a chimney is built "inside" the walls of a home, the surrounding combustibles are the framing. In Canada, my internal masonry chimney, with it's original clay liners, requires a two inch air gap external to the bricks from adjacent combustibles. That seems hard to construct, and even harder to confirm if you aren't the one who built the home.
If the chimney was originally built for an oil fired appliance, it didn't require an air gap given the lower temps it would experience. Lots of these chimneys are now being used for burning wood without folks realizing that they aren't built for the temps they will experience.
So, unless you can confirm that your masonry chimney meets the code requirements of the area you are living in, you probably need to insulate your liner.
Question # 2 - Or should I say "install an insulated liner"?
I would prefer saying "install an insulated liner" over "insulate your liner". Why? Not all liners can be insulated, and not all insulated liners will reduce the clearances to the point that your chimney may require. This is where testing and instructions come in. In the legal, bureaucratic world, testing is the only thing that counts. So insulating any new liner may not meet the mark. If legal, bureaucratic issues don't concern you, you can stop here. Note that they do likely matter to your insurance company though, or your building inspector. I wish they mattered to more installers, but sadly they don't matter to but a few. Most of them post here.
A liner gets tested by folks like ULC or Warnock Hersey by setting it up in a lab in the configuration required by its accompanying instructions. What they state in the end is that when the product is used as designed by following the instructions, it meets certain safety and performance specs. Just because company X makes a certified liner out of a given thickness metal and company Y makes theirs the same way out of the same stuff, doesn't make company Y's product "certified". The testing looks at install instructions as well. Also, testing costs money, and each configuration to be tested costs more money, so some companies won't pay the extra, and are happy to sell the liner without any certified methods for insulating the liner.
In the end, if you answered yes to the first question, then you need to buy a liner that can be insulated in a way that will bring your previously non compliant chimney "up to code" by reducing the required clearances to what actually exists in your house. The way that the liner can be insulated will vary between manufacturers
Question # 3 - Aren't you being overly picky?
Maybe, but I bet you measured the floor in front of your stove to make sure you had the 18 inches the instructions said you needed for ember protection. You likely even bought double walled smoke pipe because it didn't need the large distances from the wall and ceiling that single wall pipe needs. You even measured around the stove to make sure the TV stand was far enough away.
You see, stove instructions are well written in most cases, and we have learned to follow them. Installers know to read them. But flue liner instructions are often not well written. I'm going to guess most folks don't even know they came with instructions.
Remember question #1 - you started by saying you needed a code compliant chimney.
Question # 4 - What are my options?
Many options that won’t fit inside the 6000 character limit. Ideally, what you want is a liner that meets ZERO/ZERO CLEARANCE SPECIFICATIONS. That is ZERO inches between the insulated liner and the inner surface of the chimney, and ZERO inches between the external surface of the chimney and combustibles. You might get away with less, but a zero/zero install means you have met the worst case.
In the end chose the type of product that meets the clearances you require and clearly says so in it's instructions. Again - read and follow the instructions, just like you did when you had the stove put in place. If the instructions don't give you actual numbers, but instead say things like "clearances as per NFPA 211, UL 1777 etc" then I recommend you not buy that liner unless you know what those technical documents actually say.
That should cover it. I haven't mentioned performance issues and reducing creosote in this post - suffice to say that an insulated liner will stay warmer, have less creosote condensing on it, and will draft better because it is hotter. I'll leave that to someone else's post.
I hope all this helps someone. I will at least have a post I can refer the next poster to when the question gets asked again
For folks who may still be asking the question, here is what I have learned:
Question # 1 - Do I need a Code Compliant Chimney?
Most folks ask "Do I really need to insulate my liner?" The question could be better phrased "Do I really need a Code Compliant Chimney?" If you believe you do need your chimney to meet code, keep reading. Many masonry chimneys don't meet building code requirements, as they were not built with the required one or two inch external air gap to combustibles that is required for wood fired appliances. I say one or two inch air gap because the gap required depends on many things, like whether you are in Canada or the USA, or whether the chimney is on an outside wall of the building or not.
This air gap keeps the heat that can occur during a chimney fire (2100*F flue gas temp) from damaging surrounding combustibles. In most cases, like when a chimney is built "inside" the walls of a home, the surrounding combustibles are the framing. In Canada, my internal masonry chimney, with it's original clay liners, requires a two inch air gap external to the bricks from adjacent combustibles. That seems hard to construct, and even harder to confirm if you aren't the one who built the home.
If the chimney was originally built for an oil fired appliance, it didn't require an air gap given the lower temps it would experience. Lots of these chimneys are now being used for burning wood without folks realizing that they aren't built for the temps they will experience.
So, unless you can confirm that your masonry chimney meets the code requirements of the area you are living in, you probably need to insulate your liner.
Question # 2 - Or should I say "install an insulated liner"?
I would prefer saying "install an insulated liner" over "insulate your liner". Why? Not all liners can be insulated, and not all insulated liners will reduce the clearances to the point that your chimney may require. This is where testing and instructions come in. In the legal, bureaucratic world, testing is the only thing that counts. So insulating any new liner may not meet the mark. If legal, bureaucratic issues don't concern you, you can stop here. Note that they do likely matter to your insurance company though, or your building inspector. I wish they mattered to more installers, but sadly they don't matter to but a few. Most of them post here.
A liner gets tested by folks like ULC or Warnock Hersey by setting it up in a lab in the configuration required by its accompanying instructions. What they state in the end is that when the product is used as designed by following the instructions, it meets certain safety and performance specs. Just because company X makes a certified liner out of a given thickness metal and company Y makes theirs the same way out of the same stuff, doesn't make company Y's product "certified". The testing looks at install instructions as well. Also, testing costs money, and each configuration to be tested costs more money, so some companies won't pay the extra, and are happy to sell the liner without any certified methods for insulating the liner.
In the end, if you answered yes to the first question, then you need to buy a liner that can be insulated in a way that will bring your previously non compliant chimney "up to code" by reducing the required clearances to what actually exists in your house. The way that the liner can be insulated will vary between manufacturers
Question # 3 - Aren't you being overly picky?
Maybe, but I bet you measured the floor in front of your stove to make sure you had the 18 inches the instructions said you needed for ember protection. You likely even bought double walled smoke pipe because it didn't need the large distances from the wall and ceiling that single wall pipe needs. You even measured around the stove to make sure the TV stand was far enough away.
You see, stove instructions are well written in most cases, and we have learned to follow them. Installers know to read them. But flue liner instructions are often not well written. I'm going to guess most folks don't even know they came with instructions.
Remember question #1 - you started by saying you needed a code compliant chimney.
Question # 4 - What are my options?
Many options that won’t fit inside the 6000 character limit. Ideally, what you want is a liner that meets ZERO/ZERO CLEARANCE SPECIFICATIONS. That is ZERO inches between the insulated liner and the inner surface of the chimney, and ZERO inches between the external surface of the chimney and combustibles. You might get away with less, but a zero/zero install means you have met the worst case.
In the end chose the type of product that meets the clearances you require and clearly says so in it's instructions. Again - read and follow the instructions, just like you did when you had the stove put in place. If the instructions don't give you actual numbers, but instead say things like "clearances as per NFPA 211, UL 1777 etc" then I recommend you not buy that liner unless you know what those technical documents actually say.
That should cover it. I haven't mentioned performance issues and reducing creosote in this post - suffice to say that an insulated liner will stay warmer, have less creosote condensing on it, and will draft better because it is hotter. I'll leave that to someone else's post.
I hope all this helps someone. I will at least have a post I can refer the next poster to when the question gets asked again
