I went to the local dealer to grab some materials for a Jotul c450 install and couldn't escape without getting an installation spiel. The advice was that if I am using a complete flex liner from stove to roof cap that I don't need a block off plate and instead should stuff fiberglass insulation around the liner at the damper location(thats how they do it). If I do, I shouldn't seal it( I mentioned using silicone). Also, I should not install any insulation around the liner at chimney top, the reason being that the heat needs to escape from the chimney cavity around the liner. My liner is not insulated (flex king pro), and I planned on installing a block off plate, use mineral wool insulation, and to pack mineral wool around the liner at the chimney top. Am I off base? My logic was to intentionally trap heat in the chimney to get a better draft and keep the heat in the house. Would this somehow damage the chimney?
Dealer install advice is conflicting
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Ctwoodtick
Minister of Fire
My non- pro opinion. Block off plate is much desired, not needed per code. You will save a good amount of heat with bottom block off plate, but use rock wool type insulation. Not fiberglass.
Insulating the top of chimney seems like overkill to me. I’m all not sure how it would all stay up there. But I suppose it wouldn’t hurt if using rockwool insulation.
For what you are installing, the way I would want it done would be to insulate the liner for sure. No point in heating up the masonry, you’re only losing heat. Insulation serves a big purpose in the event of a chimney fire. Plus, creosote buildup will be less in an insulated liner.Block off plate made of sheet metal fitted to damper area with Rockwell sitting on that sheet metal. Again, much preferred but not totally needed.
I’ve found that advice from stove shops can be bad. Advice here on Hearth is usually very good and you rest assured no one here is trying to sell you something.
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I forgot to mention I have an interior chimney, I would think that more heat in the masonry means more heat in the house and less out the top as long as it's pulling draft, just guessing though. Interestingly, the inspector doesn't care about the chimney or firebox condition or whether there is a liner, only a good connection to the insert and combustible clearances met.
Ok the dealer is clueless. They are right in that you don't need a block off plate. But you absolutely want one to direct as much heat as possible into the room. Their use of fiberglass is completely wrong it doesn't have a high enough heat rating for that use. And no you don't want the heat to escape out the top of the chimney you want to keep as much heat as possible in the liner. Which is why you should absolutely be insulating the liner both for performance and safety reasons. Infact you are probably required to do so by code unless your chimney has 2" clearance to combustibles from the outside of the masonry structure.
I asked specifically about insulating the liner to the inspector, an installer when getting a quote, and two local dealers. None of them even flinched about insulating the liner. I'm ignorant on that, apparently it's local code specific.
It is not local code specific. It is part of the international residential code. Which Oregon adopted. Did they even ask about chimney clearances.
Look up IRC chapter 10
R1003.18 covers chimney clearances.
If your chimney doesn't have those clearances on a new install you are required to bring it up to code by insulating the liner
R1003.18 covers chimney clearances.
If your chimney doesn't have those clearances on a new install you are required to bring it up to code by insulating the liner
Ctwoodtick
Minister of Fire
Yes the heat lost to the masonry chimney would come back to you to some degree with internal chimney but insulating liner to keep the stove/liner running efficiently is the best thing to do.
I will look that up. I asked whether the chimney or firebox needed to be checked out before I installed anything and got a clear "no". He said to install everything except for the surround so he could see the liner connection to the insert. No mention of chimney clearances. I see that misspoke earlier, the inspector asked whether the liner went to the top of the chimney but didn't care about it being insulated.
Ctwoodtick
Minister of Fire
I will be installing this myself as soon as all the materials arrive next Tuesday. I read the IRC chapter 10 R1003.18. There is an exception to the 2inch minimum clearance:
Quote
Exceptions
1. Masonry chimneys equipped with a chimney lining system listed and labeled for use in chimneys in contact with combustibles in accordance with UL 1777 and installed in accordance with the manufacturers instructions are permitted to have combustible material in contact with their exterior surfaces.
The flex king pro liner is UL 1777 listed according to their website. Now, I would say that someone would need to do their own research for their particular application and check with your local code brute squad as I cherry picked this quote out of a whole lot of other regulations. I could be misinterpreting something but how it reads I would think I am ok if my install gets properly interrogated.
Quote
Exceptions
1. Masonry chimneys equipped with a chimney lining system listed and labeled for use in chimneys in contact with combustibles in accordance with UL 1777 and installed in accordance with the manufacturers instructions are permitted to have combustible material in contact with their exterior surfaces.
The flex king pro liner is UL 1777 listed according to their website. Now, I would say that someone would need to do their own research for their particular application and check with your local code brute squad as I cherry picked this quote out of a whole lot of other regulations. I could be misinterpreting something but how it reads I would think I am ok if my install gets properly interrogated.
It is not listed for zero clearance under ul 1777 without insulation. Infact most are not rated for solid fuel at all without insulation because they were never tested that way. Read the manufacturers instructions regarding zero clearance.
I am not talking about doing it to pass inspection. No inspector will ever know they honestly are pretty clueless when it comes to chimneys. This code was made because of a large number of fires caused by heat transfer to adjacent combustibles. Code is about keeping you safe.
It is your choice if you go with insulation or not. As I said the inspector will never know. But insulation is pretty cheap for the benefits it provides in safety and performance. And regardless of passing inspection or not it is required by code unless you have those clearances
The other reason for a block off plate (other than preventing heat from going up) is to avoid cold air coming down when not using the stove. So plate and (silicone) seal (and insulation, rockwool, not fiberglass).
Gotcha, I'm not trying to skate by but dont want go overboard if not necessary. It's hard to interpret all the internet experts on what is truly required and what is "a good idea"(no offense anyone). Interesting about the UL 1777 rating as advertised when they sell their package deal without the insulation. I would think they would go out of their way to push it on you to pad the price and point out the code requirement for solid fuel use. I'll check out the manufacturers info.
To be clear from a code perspective, if my chimney does in fact have the required 2" clearance then the insulation is a performance benefit, not a safety requirement?
Thank you all by the way for the help and input, very much appreciated!
To be clear from a code perspective, if my chimney does in fact have the required 2" clearance then the insulation is a performance benefit, not a safety requirement?
Thank you all by the way for the help and input, very much appreciated!
Great, thank bholler. I will at least crawl in the attic and get an idea of clearances. If things look close I will need to consider my options.
Sweep the existing chimney real well before installing the liner.
Gotcha. I did that a few weeks ago. The flue was actually really clean, just a gray haze on the clay liner before I did anything. I crawled up in the attic today and definitely no 2" clearance. Found a couple dead critters and some old newspaper buried under the blown-in insulation. Papers from the same year the house was made in 1950 and through 1962. Even an article about the Bay of Pigs incident. Anyway, looks like my only options are to run a non-insulated liner or bust out the clay liner. There is no room for an insulated liner in my current flue. This leads me to another question; does this mean that my existing fireplace in the adjacent flue is out of code as well?
Just to clarify, do you mean 2 inches from the block chimney or from the liner inside? What if it’s a stainless steel liner in a clay liner with a concrete block exterior. I’m questioning out of curiosity.
2" from the outer surface of the masonry structure to any combustible materials for an internal chimney. It's 1" for an external chimney.
An uninsulated stainless liner inside clay inside block still needs clearances. The only thing that changes that is insulation
That's just fantastic... That's a separate project to tackle. Anyway back to flue that will get the liner, I looked at the bottom of the flue and it looks like the clay liner is sitting right on the brick of the chimney. Even if I knocked out the liner the opening to the smoke chamber wouldn't get any bigger without chiseling the structural brick of the chimney. Is it normal and ok to do that? In the attached pic, notice the wall of the clay liner sitting on the brick. I will have to completely demolish the smoke shelf to fit up there.
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