Liner in existing air cooled metal chimney-replace top cap?

[par38lamp]

I have a 8" air cooled (double walled) chimney. It of course has a top cap at the top. When I go to reline it with 6", should I replace the existing top cap (in good shape), or remove it and try to make the new 6" cap work?

I was thinking of letting the 6" liner stop just below the existing cap, leaving well enough alone. Ensuring that the 6" is sealed from the 8" to keep smoke from getting down the gap between the 6" and 8".

Do I need to block off the air gap between the inner and outer walls?

Thanks!

 

[DiscoInferno]

I think you want to remove the exiting cap, bring the liner out above the 8", attach a blockoff plate to hold the liner and seal the gap between the liner and original chimney, and use the new cap. But I'm not really the guy to answer these questions. Are you planning to insulate the liner? I may be doing the same thing in the next year in an external chase in a cold climate, so I want/need insulation, but I'm not sure if an insulated 6" ID liner will fit down an 8" ID chimney.

 

[par38lamp]

I have given serious consideration to insulating the liner, but while searching for Lopi Revere owners on this board, a few have suggested to not insulate the liner unless you are having bad draft. IE, install it without, and the go back and insulate it later if there is trouble. I am still up in the air.

I agree with what you describe. The new top cap would be an easy way to cap the double wall there now. Problem is working on my roof. Steep pitch, 2 story.

 

[wahoowad]

I would love to see pics of how someone terminated the top connections on an installation like this! I just can't picture what the block off plate would look like.

 

[Shane]

I usually take the top half of the cap off and leave teh base. This prevents my top plate termination from blocking the airflow to the class A.

 

[seaken]

In fact, the code does not allow you to block off the air flow between the inner and outer walls of your existing chimney. I have used Shane's technique also. Homesaver makes a special top plate that solves this problem.

 

[MountainStoveGuy]

doesnt air cooled pipe need a insulated liner to bring it up to UL1777?

 

[Shane]

Typically yes, the last time I brought up the UL1777 thing I was run out of here with a big stick though.

 

[MountainStoveGuy]

its pretty black and white...
air cooled ZC pipe is rated for 1800*
stoves and inserts require 2100*
the only way to make a AC pipe rated for 2100* is to drop a liner down it with a 1/4" of insulation....

 

[elkimmeg]

There are two ul listings for ZC fireplaces one that list the linner to 1700 degrees and one that is the 2100 degrees Class A

If it is class A 8" a 6" pipe may be direct connected, though not that good of an idea or draft situation

If it is rated to 1700 degrees than to burn a wood stove it must be insulater to achieve UL 1777 meaning 1/2 " insullation
The ventelated air space can not be blocked at the cap. Home Saver does make just such a cap that is tested with their liner and allows the former ventilated pipe to function

 

[MountainStoveGuy]

isnt air cooled and double wall both considerd class A ?
should that statement read that you can direct connect 6" to 8" double wall, but not to air cooled double or tripple wall (zc fireplace pipe)?

 

[DiscoInferno]

In fact, the code does not allow you to block off the air flow between the inner and outer walls of your existing chimney. I have used Shane's technique also. Homesaver makes a special top plate that solves this problem.

I didn't mean to block the air space between inner and outer pipes in the original chimney, I meant to block off the air flow between the new liner and the inner (8") chimney pipe. The liner isn't meant to be air-cooled, correct?

 

[MountainStoveGuy]

In fact, the code does not allow you to block off the air flow between the inner and outer walls of your existing chimney. I have used Shane's technique also. Homesaver makes a special top plate that solves this problem.

I didn't mean to block the air space between inner and outer pipes in the original chimney, I meant to block off the air flow between the new liner and the inner (8") chimney pipe. The liner isn't meant to be air-cooled, correct?

correct.

 

[DiscoInferno]

its pretty black and white...
air cooled ZC pipe is rated for 1800*
stoves and inserts require 2100*
the only way to make a AC pipe rated for 2100* is to drop a liner down it with a 1/4" of insulation....

My Ultima has a double-wall (6" inner, 11"? outer) air-cooled chimney. It's made by Security (who makes the Ultima) and is specifically listed for use with the Ultima, but other than that I don't have any info on it. I assumed it was rated to 2100, since it's really a stove in a ZC form factor.

Edit: I looked up the requirements for my Majestic WMC42 prefab - it's designed to use 8" ID triple-wall CFM "Model S" chimney, which seems to be rated to 2100. So can I really try a direct-connect on that? Seems doomed to disappoint given the cold climate and chimney length (less that 20' I think), but easy to try.

 

[par38lamp]

Wow. Really learned something here! Leave existing air cooled chimney vented, and seal off the air space between the inner existing pipe and new 6" liner. Insulate the liner to meet UL 1777.

 

[seaken]

I'm not sure how Class A is defined. But I do know that the UL test used to be set at 1700* F and then is was upped to 2100*. From that point on we have used the term "Type HT" to distinguish the type of pipe meant for controlled combustion wood stoves. We still use the term Class A but I think most of us who use that term mean it to be packed insulated or hybrid packed+air type chimneys meant for freestanding applications. It's confusing.

For inserting a wood stove/insert into a fireplace the chimney is only part of the equation. To qualify for ANY type of UL approval both the fireplace and the stove/insert must be tested as apprived for this purpose. These days, few insert installs qualify as UL approved even when the chimney liner is insulated. BOTH fireplace and insert must be a matched set to qualify. It is usually decided on a case by case basis and an effort to match up a UL listing is not usually attempted. When we are asked to install an insert into a ZC fireplace we usually decide based on the quality of the ZC fireplace and it's being installed correctly and then the stove/insert itself being approved for use with a ZC. If we are comfortable with the combination we then decide on whether the liner should be insulated. If the ZC fireplace does not specifically allow inserts we require insulation. If the ZC allows inserts then we may allow an uninsulated liner. But in all cases we do a full re-line.

Only when the ZC and the insert are a matched set, and qualify as UL approved, can a direct connect be allowed. And yes, a direct connect was allowed under the rules for inserts into approved ZC fireplaces. But we always felt more comfortable doing a full reline. We could never sort out the "Type HT" requirment for our inserts when compared to direct connect to a ZC air-cooled chimney that clearly was not intended for use with a controlled combustion wood stove. But then again, the BIS is a good example of a controlled combustion "stove" that is approved for an air-cooled pipe. We've never been comfortable with using air-cooled pipe for this purpose but it is UL Listed. Does that mean that this air-cooled pipe can be termed "Class A" or "Type HT"? Who knows? All I know is that the UL Listing only works when the "system" stays together as a "fireplace system". The pipe was not tested to classify as a pipe for free standing wood stoves, what we call "Class A".

We take the stand that air-cooled chimney should not be used for controlled combustion stoves/inserts without a full reline. If a UL listing is wanted or required then a suitable insulation and block-off system must be used.

 

[elkimmeg]

OL 103 has two classifications UL 103 is tested to 1700 degrees and can be used in prefab fireplace venting not for wood stove usage
it has only been tested with that pre fab fireplace

UL 103 HT is tested to 2100 degrees the only acepted approved usage for wood stoves. A prefab manufacture may have tested and spect HT 2100 ( UL103)
they can use either or. If the one in question his Ul 103 HT, it can be used direct connected. IF it is the lesser only 103 and not HT
a UL1777 insulated liner is required for wood stove applications. The ventalated air space cannot be blocked .Home saver makes the only approved
cap for this setup. That I know of

This is not guess work but actual code and UL listings The only discussion is the meaning of ClassA To me class A is UL 103 HT

 

[DiscoInferno]

Here's what I found on the chimney that is (supposed to be) on my Majestic. UL 103 HT it is.

Is triple-wall air-cooling of the sort described any better than double-wall for the purposes of draft and creosote, since the air that hits the actual flue is preheated in the outer chamber?

2.8 Majestic Model "S", 8-inch, Type HT 2100/F
Chimney System:
This chimney system, which includes rooftop assemblies,
flue supports, firestop spacers, chimney components and
elbows, complies with Underwriters Laboratories Inc.
Standard UL 103, as a "Type HT" chimney system for use
with solid-fuel-burning appliances specifically recognized in
an ICBO ES evaluation report. All chimney system
components are marked "Type HT." The basic construction
is of concentric cylinders, the outer section of galvanized
steel, an inner section of aluminized steel and a flue
section of minimum 0.015-inch-thick (0.38 mm) stainless
steel. The products of combustion flow through the flue
section. The inner section has four spacers attached so as
to ensure an air space between the flue and the inner
section, and between the inner and outer sections. Cooling
air is drawn down the space between the inner and outer
sections, while the space between the inner section and the
flue is used for expelling the heated cooling air. A flue
support shall be installed at or below the 30-foot (9 m)
height if the height of the chimney exceeds this dimension.
Two flue supports are required for a chimney installed at its
maximum height. Refer to Table 3 and Figure 8 for further
details.

 

[seaken]

Here's what I found on the chimney that is (supposed to be) on my Majestic. UL 103 HT it is.

Is triple-wall air-cooling of the sort described any better than double-wall for the purposes of draft and creosote, since the air that hits the actual flue is preheated in the outer chamber?

2.8 Majestic Model "S", 8-inch, Type HT 2100/F
Chimney System:
This chimney system, which includes rooftop assemblies,
flue supports, firestop spacers, chimney components and
elbows, complies with Underwriters Laboratories Inc.
Standard UL 103, as a "Type HT" chimney system for use
with solid-fuel-burning appliances specifically recognized in
an ICBO ES evaluation report. All chimney system
components are marked "Type HT." The basic construction
is of concentric cylinders, the outer section of galvanized
steel, an inner section of aluminized steel and a flue
section of minimum 0.015-inch-thick (0.38 mm) stainless
steel. The products of combustion flow through the flue
section. The inner section has four spacers attached so as
to ensure an air space between the flue and the inner
section, and between the inner and outer sections. Cooling
air is drawn down the space between the inner and outer
sections, while the space between the inner section and the
flue is used for expelling the heated cooling air. A flue
support shall be installed at or below the 30-foot (9 m)
height if the height of the chimney exceeds this dimension.
Two flue supports are required for a chimney installed at its
maximum height. Refer to Table 3 and Figure 8 for further
details.

Thanks Disco. Where did you find this info? In the manual for your fireplace?

Note that the WarmMajic can use either the Two-wall SK-8 series or the Triple-wall 8" S series. I wonder if they are both tested to 2100*F? I'll see if I can find out.

And yes, I think the triple-wall is a better choice than two-wall for air-cooled chimneys. But many fireplaces do not suport triple-wall. All the current high-efficiency fireplaces that we sell support only the two-wall variety (BIS, VC/Majestic Sequoia, FPX Elite).

 

[seaken]

OL 103 has two classifications UL 103 is tested to 1700 degrees and can be used in prefab fireplace venting not for wood stove usage
it has only been tested with that pre fab fireplace

UL 103 HT is tested to 2100 degrees the only acepted approved usage for wood stoves. A prefab manufacture may have tested and spect HT 2100 ( UL103)
they can use either or. If the one in question his Ul 103 HT, it can be used direct connected. IF it is the lesser only 103 and not HT
a UL1777 insulated liner is required for wood stove applications. The ventalated air space cannot be blocked .Home saver makes the only approved
cap for this setup. That I know of

This is not guess work but actual code and UL listings The only discussion is the meaning of ClassA To me class A is UL 103 HT

elk, I can't remember. Does UL127 include the UL103 tests? As I understand it factory built fireplaces are tested to UL127. If a chimney system is not tested as a standalone chimney to UL103 it cannot be considered "Class A". Is that correct?

 

[DiscoInferno]

Thanks Disco. Where did you find this info? In the manual for your fireplace?

Note that the WarmMajic can use either the Two-wall SK-8 series or the Triple-wall 8" S series. I wonder if they are both tested to 2100*F? I'll see if I can find out.

From the (broken link removed to http://www.vermontcastings.com/catalog/elements/files/2006/20000583_WMC.pdf) and the Majestic (broken link removed to http://www.vermontcastings.com/content/products/productdetails.cfm?id=109) I found out which chimney it uses. It seems that most of the Majestic fireplaces can use either the SK-8 series or the S series, but I see conflicting info for the WMC42 specifically. The manual suggests that both the WMC36 and WMC42 can use both types, but then page 9 of the manual has the following crystal-clear :-S text:

NOTE: The WMC36 may use CFM Corporation model
SK8, or Model S (three wall) chimney systems. How-
ever, a TWABR adapter collar is required when using
the Model S (triple wall) chimney system on this unit.
The WMC42 is designed to use only the "S" triple wall
chimney system. Either chimney system may be used,
but must not be mixed.

So is it only the "S", or either? I don't know, and I don't know what my WMC42 actually has. I have pictures of some of the sections before they were installed, but they have cardboard over the ends so I can't count the pipes and I'd need one of these magic "CSI" photo-enhance tools to read the lettering. Looks wide enough in the photos to be the triple wall. I'll probably have to call the modular home company, or climb the roof.

The info on the chimney I found via google from (broken link removed to http://icc-es.org/reports/pdf_files/ICBO-ES/5677.pdf), which also indicates that the WMC42 in particular is only designed for the S series. The pdf does not seem to have info on the SK-8 chimney.

 

[elkimmeg]

OL 103 has two classifications UL 103 is tested to 1700 degrees and can be used in prefab fireplace venting not for wood stove usage
it has only been tested with that pre fab fireplace

UL 103 HT is tested to 2100 degrees the only acepted approved usage for wood stoves. A prefab manufacture may have tested and spect HT 2100 ( UL103)
they can use either or. If the one in question his Ul 103 HT, it can be used direct connected. IF it is the lesser only 103 and not HT
a UL1777 insulated liner is required for wood stove applications. The ventalated air space cannot be blocked .Home saver makes the only approved
cap for this setup. That I know of

This is not guess work but actual code and UL listings The only discussion is the meaning of ClassA To me class A is UL 103 HT

elk, I can't remember. Does UL127 include the UL103 tests? As I understand it factory built fireplaces are tested to UL127. If a chimney system is not tested as a standalone chimney to UL103 it cannot be considered "Class A". Is that correct?[/quote

agree the pre fab stoves are listed toUL 127 however each manufacturer in his listing can submit to 1700 Ht 103 only manufacture rx may submit his listing to 103 HT there also can be a dual listing of both 103 and 103HT You now know why I require this info and enter it in public records the same reason I require the liners to be identified and a copy of the listing entered in the folder of each home work is done. One can come to my office and find out what was installed. I also make inspection notes indicating whether a block off plate was installed .

I'm guessing here but the pre fab must meet 127 and list the UL approved liner