To insulate or Not?

[offroadaudio]

The answer for me is YES - but I found this info and thought it might make good reading fodder for the masses.......


One of the questions I hear most often from sweeps and fireplace retailers is "When should I insulate a chimney liner?" It's a great question that requires a detailed answer. The most relevant question to many installers regarding insulating chimney liners is "When do I HAVE to insulate one?" This requires looking at the NFPA 211 standard for masonry chimneys and the UL 1777 listing.

NFPA 211 is the code set forth by the National Fire Protection Association for the construction of masonry chimneys. To summarize the code, a masonry chimney is up to the standard when it is built with two critical one-inch air spaces. One between the combustibles outside of the masonry chimney and one between the chimneys masonry structure and the chimneys interior flue tile. Unfortunately, chimneys built up to the NFPA 211 standard are more the exception than the rule.

UL 1777 is the listing which lays out the installation guidelines for stainless steel chimney liner installations intended for solid fuel applications. These are an overwhelming majority of installations performed by chimney sweeps and fireplace retailers and are the installations where, typically, insulation is an issue. The results of the stringent testing process a chimney liner must go through in order to carry the full UL 1777 listing is what determines the specific insulating requirements for each specific chimney liner. During a simulated chimney fire, UL measures the amount of heat transferred from within the liner to the exterior of a non-conforming masonry chimney. If UL measures too much heat transfer, then the liner fails the test. Given the nature of any single wall chimney liner, heat transfer of an uninsulated liner is going to be high. With high density insulation, heat transfer is reduced tremendously. This allows for a safe installation even in a non-conforming chimney, thus allowing a "Zero Clearance" installation.

Any stainless steel chimney liner that carries the full UL 1777 listing can be installed to what is commonly referred to as "Zero Clearance" so long as it is installed in conjunction with its installation instructions. These instructions are laid out by the manufacturer and Underwriters Laboratories or the liners listing agency.

Understanding zero clearance

What specifically does Zero Clearance mean? The Zero Clearance rating refers to the amount of airspace between the chimney liner and the inside of the masonry chimney. It also refers to the airspace between the exterior of a masonry chimney and combustibles. For this reason the listing is sometimes called "Zero - Zero" in the field.

If the chimney liner you are installing carries a full UL 1777 listing to Zero Clearance you can install, within the liner's installation guidelines, with no airspace between it and the inside of the masonry chimney. This also is the case when the chimney has no air space

A liner which carries the full UL 1777 listing can be installed to Zero Clearance within the chimney without insulation so long as the masonry chimney it's installed into meets NFPA 211. Again, if the masonry chimney does not meet the NFPA 211 standard, insulation is required.

What does this mean for the installer in the field? Given that NFPA 211 chimneys are the exception and not the rule, it means you should plan on insulating nearly all of the stainless steel chimney liners you install, if you want them to be up to the UL 1777 standard.

 

[offroadaudio]

PART 2

Determining type and quantity

You now need to know what kind of insulation and how much of it to use. This is determined by UL for each individual chimney liner manufacturer as their product is tested. Ask your chimney liner manufacturer for their specific written UL-approved insulating guidelines. If they can't provide them, odds are that their chimney liner hasn't been fully tested for solid fuel applications.

The insulation requirements necessary to install our liner product to Zero Clearance in a non-conforming masonry chimney are 1/2" of 8 lb. density foil faced ceramic blanket insulation. This level and type of insulation is typical of many chimney liners carrying a full UL 1777 listing. Again, ask the liner manufacturer you're working with for their specific requirements.

What if you are already dealing with a NFPA 211 standard chimney? Again, you don't HAVE to insulate that chimney liner installation.

When to insulate

Getting back to the original question of "When should I insulate a chimney liner," my answer is "always." I would argue that there are tremendous benefits to insulating all chimney liners. Reduced creosote adhesion, reduced heat transfer and improved draft all make insulating a chimney liner an excellent option for providing the homeowner a cleaner, safer, and better operating installation.

We all know the fuel for chimney fires is heavily condensed creosote. If we eliminate its build up in the first place, we have put out a chimney fire before it's started. The inherently hotter internal surface of an insulated chimney liner is less likely to have creosote build up.

Creosote typically condenses only after it has cooled or come in contact with a cooler surface. By keeping the internal temperature of a chimney liner high, creosote doesn't have the opportunity to condense within the liner system. To the benefit of the homeowner, the uncondensed exhaust simply vents into the atmosphere.

Related to the already discussed listing issues, there is a limitation of heat passing from the liner system to the masonry chimney and therefore onto combustibles. This nearly eliminates the possibility of a chimney fire by passing enough heat from the chimney liner via masonry chimney to combustibles to start a house fire. This combined with the previously noted reduction in creosote adhesion gives the homeowner the highest level of safety from chimney fires available.

Optimum draft levels, as we all know, greatly improve the performance of nearly all solid fuel burning appliances. An insulated chimney liner contains heat within it creating a hotter thermal column. This optimizes draft conditions, which is especially beneficial when one considers how draft dependent today's modern wood stoves are. Optimizing draft is essential for today's solid fuel appliances with their catalytic combusters and large air wash glass doors. Even the finest of heating appliances, when installed into a chimney that is not drafting at its optimum level, can leave the homeowner unsatisfied, giving the retailer, installer and homeowner a headache that very easily could have been avoided.

In conclusion, plan on insulating most of the chimney liners you install for solid fuel applications. Not only does the prevalence of masonry chimneys built below the NFPA 211 standard and the requirements of UL 1777 require insulation in most cases, but insulating those chimney liners will reduce creosote adhesion, heat transfer, and improve draft, giving your customers the best possible performance and safety from their heating appliances.

 

[begreen]

Good info ORA. For an exterior chimney, I would always insulate, but not always for an interior flue. If the wood burned is dry and creosote accumulation is not an issue to start with, there may be little to be gained, especially if the liner is in a flue that is already tile lined and in good condition. If the flue is tall, insulating the liner may actually help to create too much draft. For example, if the chimney was 28 ft and the max recommended for the stove was 30 ft, I'd probably not insulate it.

 

[jtp10181]

This is what I have been preaching here for a year or so now. But no one really listens... We insulate 100% of our liner installs because you never know if the masonry structure is up to NFPA 211 specs.

BeGreen, for interior chimneys, it is not a matter of draft or creosote, but safety. If someone has lumber anchored directly to the masonry structure hidden behind the walls somewhere this could dry out over time and eventually ignite. If you have an uninsulated liner and its touching the clay tiles the heat could transfer through if the unit is run for a long time.

 

[begreen]

Don't Simpson and other companies make spacers to keep the liner 1" away from the tile sides?

How common are fires related to this issue? Are there a lot of fires created by heat transference in tile lined chimneys with good stainless liners?

 

[oconnor]

I have also been preaching the same. I wish more installers here in Nova Scotia had a clue about the issue. I've been recommending the Best Practices guide to those who are looking into a liner install (link in my sig block).

 

[jtp10181]

Don't Simpson and other companies make spacers to keep the liner 1" away from the tile sides?

How common are fires related to this issue? Are there a lot of fires created by heat transference in tile lined chimneys with good stainless liners?

Yes they do make spacers, I would have to check their info again but I still think the existing masonry needs to be built to NFPA 211 specs even if you use the spacers. Their liners are tested for 1" clearance to masonry if uninsulated and 0" with the insulation. The only way the liner system meets UL 1777 is with 1/2" insulation wrap. Without the insulation you rely on the masonry structure for the "safety" aspect and liner is simply to re-size the flue.

We have not had any fires in our area that I know of, but I did talk to a guy at the corporate level in our company about this last year and he said he has been to many fire scenes around the country caused by improper liner installation. He said there is not major danger for a casual burner but lets say someones power goes out for a week and they have their unit cranking hard for 7 days. Eventually the whole masonry structure or prefab pipe will become a thermal mass and this is when it gets dangerous.

 

[begreen]

I can appreciate that. Back in the 60's my wife's home was an old inn built entirely out of chestnut. There were two big fireplaces, one above the other and no central heat. During one very cold winter spell, we had both fireplaces running 24/7 just to keep the place habitable. One night, there was smoke in the upper bedroom. It took some quick action and a lot of water to cool down the hearth. Apparently the old Yankee that built the place hadn't thought about the heat transference from the massive granite hearth to the supporting chestnut timbers. All was well, but it could have turned out ugly.

 

[Wet1]

If the flue is tall, insulating the liner may actually help to create too much draft. For example, if the chimney was 28 ft and the max recommended for the stove was 30 ft, I'd probably not insulate it.

This is my concern. My flue is close to 35' and interior on 3 of 4 sides (the forth is covered with studs, insulation, and siding), so I guess you could call it an interior chimney. The chimney isn't in the greatest shape, but the flue is lined with clay. I'm sure there is some cracking in the clay, so by code I know I need to insulate the 6" SS liner. I will be insulating it for safety within the next 9 months, but I'm concerned about having too much draft.

Thoughts?

 

[begreen]

Simpson will tell you no for reducing the flue diameter. But some stove manufacturers and some of our most experienced burners here have found dropping down 1/2" to be the ideal solution for very tall flues. Have you asked your Harman dealer for an opinion?

 

[Wet1]

Simpson will tell you no for reducing the flue diameter. But some stove manufacturers and some of our most experienced burners here have found dropping down 1/2" to be the ideal solution for very tall flues. Have you asked your Harman dealer for an opinion?

You lost me BG, why would I want to drop the liner size down below 6"? Wouldn't this increase draft a little more by increasing velocity, or would the reduced area decrease draft??

 

[TKeller]

Could another valid reason for insulating a liner installlation inside a clay flue be if.......your original clay liner has alot of hard glazed creosote and the insulation would help keep the hot liner from igniting the glazed creosote? The really good chimney sweep in my area said so. So that is one reason I insulated my liner, just in case. Personally, I don't feel up to this point that my new insulated 6 inch liner drafts any better than with my old stove slammed into my fireplace with a 12x12 inch clay liner. I smell smoke more now when I go to reload than I did with the old stove. Tony

 

[jtp10181]

Really if you do it right, with the 1" spacers or with the insulation, either way would keep it from leaning on the old creosote. Problem is... most people don't do it right and just throw the 6" SS liner down with nothing on it.

I hope you are least getting more heat with less wood out of your new stove.

 

[theheatelement]

is the entire chimney covered in brick or clay.. from what you say some of it is studded if that is the case you cannot use flex liner at all... please elaborate..

best regards,

 

[jtp10181]

Sounds like a full brick chimney that was studded over on the outside to put up vinyl siding.