Flue pipe in a chimney with creosote and cracks

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.

insertnoob

New Member
Oct 9, 2021
3
Earth
I'm in the process of purchasing an insert for my house (built in 1968), which has an original chimney liner. The liner is made from clay and it has a few minor cracks as well as a build-up of creosote. The fireplace hasn't been used in many years, but my wife is all over me about buying and installing an insert. I will be installing a 6" flue pipe, but I'm not sure if I need to repair the cracks and remove the creosote first. My gut is telling me that it doesn't matter, but I can't find a definitive answer in any of the NFPA codes and searching for the last few hours didn't yield an answer either. Any advice would be greatly appreciated.
 

begreen

Mooderator
Staff member
Nov 18, 2005
91,299
South Puget Sound, WA
Yes, the chimney must be completely and thoroughly cleaned of all creosote before putting in a liner. This includes the smokeshelf. The 6" stainless liner should be insulated. Then there is no need to repair the current tile cracks.
 
  • Like
Reactions: Rob_Red

insertnoob

New Member
Oct 9, 2021
3
Earth
Yes, the chimney must be completely and thoroughly cleaned of all creosote before putting in a 6" stainless liner. This includes the smokeshelf. The liner should be insulated. Then there is no need to repair the current tile cracks.
What is the reason? I would like to understand the underlying concern since the liner can be installed in locations that are much more flammable without issue. It seems inconsistent.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,820
central pa
Begreen is absolutely correct. Once you install a stainless liner that old clay liner just becomes part of the masonry structure it doesn't matter at all anymore. But the chimney needs to be cleaned very well and the liner needs to be insulated
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,820
central pa
What is the reason? I would like to understand the underlying concern since the liner can be installed in locations that are much more flammable without issue. It seems inconsistent.
A liner absolutely cannot be installed in locations that are much more flammable. They can only be installed in masonry chimneys built with atleast 4" nominal solid masonry units. Those masonry units also need to have the proper clearance to combustibles unless the liner is insulated.
 

insertnoob

New Member
Oct 9, 2021
3
Earth
A liner absolutely cannot be installed in locations that are much more flammable. They can only be installed in masonry chimneys built with atleast 4" nominal solid masonry units. Those masonry units also need to have the proper clearance to combustibles unless the liner is insulated.
I appreciate the general guidance, but a reference to the applicable code is the goal.

Since I'm not an expert, I didn't know which words to use in my OP. I have since established that the pipe I'm using is called a twin-wall pipe, which, by design, is able to penetrate any material with significantly less clearance than a single-wall pipe. So, a liner 'absolutely can' be installed in combustible places (ceilings/walls with clearances of less than 2" to combustible materials according to the example components I am seeing on fireplace websites), which is the essence of my question. I've read multiple times that creosote must be removed, but I am yet to see an explanation regarding why which also cites a reliable source. Because I'm not going to make a rash decision nor do I think I have all the answers, I'm here to figure out the underlying reason if anyone is able to shed light on it.

Over the last few minutes, I found a reference in a UK building code that states the clearance should be 70 mm. I also found a website that states a 2" clearance (roughly 50 mm) must be maintained for twin-wall pipes, but there wasn't a source. It is not clear to me if the stated clearances apply within a chimney, but I will keep looking.
 

begreen

Mooderator
Staff member
Nov 18, 2005
91,299
South Puget Sound, WA
What exactly is the liner product that has been chosen?

UK building code is not relevant to a US insurance company, Colorado fire marshall or building inspector. In order to have an uninsulated liner, the chimney needs to have 2" clearance from any combustible (all the way up through the roof) if interior and 1" combustibles clearance if exterior. Do a search on this topic in this forum. It has been covered many times every year with code chapter and verse references.
 

stoveliker

Minister of Fire
Nov 17, 2019
2,793
Long Island NY
Are you (OP) sure that you are not mixing up a class A chimney and a liner? Class A chimney pipe has lower clearances than a chimney liner.

A liner is made to be in a masonry chimney (of a certain thickness). Having a layer of combustible (creosote or plywood for that matter) between liner and masonry is not ok.
 
  • Like
Reactions: Rob_Red

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,820
central pa
I appreciate the general guidance, but a reference to the applicable code is the goal.

Since I'm not an expert, I didn't know which words to use in my OP. I have since established that the pipe I'm using is called a twin-wall pipe, which, by design, is able to penetrate any material with significantly less clearance than a single-wall pipe. So, a liner 'absolutely can' be installed in combustible places (ceilings/walls with clearances of less than 2" to combustible materials according to the example components I am seeing on fireplace websites), which is the essence of my question. I've read multiple times that creosote must be removed, but I am yet to see an explanation regarding why which also cites a reliable source. Because I'm not going to make a rash decision nor do I think I have all the answers, I'm here to figure out the underlying reason if anyone is able to shed light on it.

Over the last few minutes, I found a reference in a UK building code that states the clearance should be 70 mm. I also found a website that states a 2" clearance (roughly 50 mm) must be maintained for twin-wall pipes, but there wasn't a source. It is not clear to me if the stated clearances apply within a chimney, but I will keep looking.
Well if you are going to get that way. There is no triple wall pipe on the market. There is triple wall chimney which is not a liner and is not meant to be put inside a masonry chimney. So by putting it in a chimney you are not installing per the listing requirements and that is a code violation.

If you are installing an actual liner every one of the install directions for liners that I have read tell you the chimney needs to be free of creosote deposits. That means it is required by code.

I am not going to look it up in the code books right now but I can guarantee it is required there as well.

As far as why it's needed I can tell you from seeing the results while doing an inspection after the fact for insurance reasons a fire in-between the old liner and the new one is extremely hard for firefighters to get put out and can pose a very serious danger.
 

stoveliker

Minister of Fire
Nov 17, 2019
2,793
Long Island NY
Well if you are going to get that way. There is no triple wall pipe on the market. There is triple wall chimney which is not a liner and is not meant to be put inside a masonry chimney. So by putting it in a chimney you are not installing per the listing requirements and that is a code violation.

If you are installing an actual liner every one of the install directions for liners that I have read tell you the chimney needs to be free of creosote deposits. That means it is required by code.

I am not going to look it up in the code books right now but I can guarantee it is required there as well.

As far as why it's needed I can tell you from seeing the results while doing an inspection after the fact for insurance reasons a fire in-between the old liner and the new one is extremely hard for firefighters to get put out and can pose a very serious danger.

Also, creosote is corrosive, so your liner would get attacked from the outside as well..and nothing you can do about that anymore.after putting it in a dirty masonry chimney.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,820
central pa
If you are talking about prefabricated class a chimney the clearance to combustibles is typically 2" that can be either double or triple wall with the double wall being the better product.

Twin wall pipe is connector pipe with an air space it typically has 6" clearance and cannot pass through ceilings or walls.
 
  • Like
Reactions: stoveliker