Hearth and liner questions for insert installation

[AdamC]

Hi all,

This is my first post, although I have been using this site for quite a bit of research. Thank you all for all of the great info and thanks in advance for your help with these questions.

I will be installing a Fireplace Xtrordinair 33 Elite into an old Heatilator unit. This is an old type unit built into full masonry, not a modern ZC unit.

The first question is regarding the flu liner. The existing flu is clean and in good condition (according to a certified sweep). The chimney is between the house and unheated garage. The flu tiles are 13x13. Two different local installers both told me that they do not routinely insulate flu liners and would not do so in my chimney. The dealer I am buying the insert from routinely uses 304ss liners and still does not recommend insulation. I have read many of the posts on this issue and my understanding is that insulation is required with 304 liners and possibly even with 316 or 316ti liners depending on the installation, but I could not come up with a definitive answer. Can someone clarify?

The second question is regarding the hearth extension I have to install. The manual for the insert does not specify an R or K value for the hearth or hearth extension. The existing hearth is raised about 12" off the floor and is about 9" wide. It has a wood frame with about 3" of concrete on top. I plan on extending the hearth to 20" by duplicating the existing structure, substituting a stack of wonderboard for the poured concrete. The entire sturcture I described above will then be covered by cast concrete hearth stones that are about 1.25" thick. Does this sound sufficient?

Thanks again!

Adam

 

[JohnnyBravo]

not sure on the flu, as for the hearth when i asked the inpector here he said if it had no spec anything non-combustable (other than the cheap wall tile) would suffice. 4.25" of stone should do well.

 

[jtp10181]

304SS, are they using the Simpson DuraFlex SS Kits? Those as well as every other liner I have seen requires the insulation for 0" combustible clearances to the masonry. That is the outside of the chimney, usually the framing of the house is attached right to the chimney. Since the catalog wont let me copy/paste just look on the first page with text.

http://www.duravent.com/pdf/catalogs/duraflex.pdf

In a 13x13 flue doing the insulation is the easiest, I don't know why they wouldn't just do it, unless they don't even know where they could get it or what to do with it.

 

[webbie]

IHMO, the idea that one grade has to be insulated and another not is altogether bunk.....

So let's dispense with that one.

If your chimney is already up to snuff structurally, then the insulation is probably a "extra", whereas if your chimney did not have a sound liner, you would need it with ANY grade.

Having the chimney protected from the wind and direct outside will definitely help also. So I would say -optional. No doubt it may increase performance...

The hearth sounds OK given that many layers (4-5+) of wonderboard.

 

[jtp10181]

Craig, after doing extensive research on the insulation topic I have found that the only way it would not be required is if your masonry chimney and flue is built exactly to NFPA 211 specs. To verify this you would either have to witness it being built or have a Level II or III inspection done to verify the combustibles clearances. After all this research, we are now requiring insulation on every liner we install, for the common 8x12 rectangular flues this means using rigid oval double wall insulated (so that it fits). My next subject to tackle is the block off plates (yes we are not doing them, I know... flame me now). Have to find out if we can get smaller pieces of blank metal instead of the giant 96x48 ones we get for chase top pans. Could also just cut those down smaller.

 

[BrotherBart]

That is semi-fascinating JP. You are making the assumption that the flue tiles are right up against the brick. Otherwise if there is 1" between the tiles and the brick then Duraflex would not require insulation. Not even counting the thickness of the flue tiles.

Never seen an 8X12 smacked right up against the bricks before.

 

[webbie]

Everyone here is right....that's why my post said if the chimney was currently up to snuff, then insulation would not be needed. It is only needed to bring defective chimneys up to current codes.

From a more common sense perspective, think about a 6" pipe inside a flue tile that hardly even touches the tile - even if it does touch, one is flat and the other round, so it cannot have a large surface bearing on the tile. Then you have the tile, and perhaps a little rubble and airspace around it. Then you have a chimney masonry structure that can be 4" to 6" thick - sometimes more. This usually only gets close to wood (should not touch it) at the roof level.

Some others here have suggested a few spacers here and there so the liner does not touch the sides the whole way up....obviously that would add an incredible margin of safety since air has a higher R value (at that distance) than normal insulation.

 

[jtp10181]

From what I have heard and read it would never be a good idea to assume a chimney / flue were built to code. I have actually heard it is pretty rare. Also on the Simpson DuraFlex SS you need to maintain a 1" clearance to the clay tiles without the insulation (for wood burning), with the round liner this is pretty much impossible with an 8x12 flue since the inside dimension is often less than 6" and the liner has to be ovalized. To maintain the 1" clearance you are supposed to put spacers on the liner every 5 ft.

 

[AdamC]

Hi all,

Thanks for the replies. It is discussions like these that left me confused to begin with!

The explanation I stumbled on for different grades of stainless requiring isulation was that the condensation of water vapor and creosote was more harmful to the lower grades and that insulation would minimize that condensation. I was kind of baffled by this because it is almost cost-neutral to buy the lower grade and then insulate.

I should have mentioned that I can get loose rock wool for free. I planned on stuffing it around the liner as far down the chimney as I could reach. I also considered putting it on top of a block-off plate at the original throat, but I wondered if allowing some warm air to rise from the insert into the chimney space would accomplish the same thing as insulating... keeping the liner warmer improving draw and reducing condensation?

Do the codes/guidelines specify that the liner must be insulated for it's full length?

Another question regarding the hearth... do I need to use refractory mortar outside of the firebox? There will be a mortar joint between the top surface stones and the edge of the fire box. Can someone offer a brief explanation of what makes it unique from standard mortar?

Adam

 

[Gooserider]

Insulation will improve your heating performance. Code is something that can be battled over, but IMHO the heating performance is worth it, regardless.

I suspect there are a couple reasons why dealers don't seem to want to insulate... 1. It is according to all reports a significant PITA to insulate a liner, and then more effort to stuff the insulated liner down the chimney as opposed to non-insulated. This means increased labor costs which makes it harder for a dealer who insulates to compete against one that doesn't. 2. I suspect that a large
e of the people that buy inserts / stoves are not really wanting to heat with them, but rather just have something for 'ambiance' - as such those customers don't care about performance the way that we do when we want to squeeze every BTU out of a split that we can. For those customers, the added cost of insulation isn't worth it...

As I understand it, you should insulate all but about the last 5' or so of liner where you need to go through the damper area.

Putting rock wool on the block off plate is a good idea, and especially if you don't insulate, stuffing as much as you can down the top of the chimney will help at least some.

Gooserider

 

[gpcollen1]

I have the same fireplace/chimney you have. It is very nice and wish I did not need the heat and could just burn open fires in it. I am installing a liner with no insulation. I will be stuffing some down the chimney later as a friend has promised some for free. I would wait for it but wood burning season is upon is.

 

[webbie]

From what I have heard and read it would never be a good idea to assume a chimney / flue were built to code. I have actually heard it is pretty rare.

He did mention a 13x13 tile, although I have noticed a couple of replies that addressed 8 x 12.

As far as the chimney, from afar we have to make some assumptions - he said it was inspected by a pro, and we can assume that the house was inspected by a building official. Still, I agree with the premise that many masonry chimneys are not build up to code. Even if they were, it is already proven that they would fail the UL tests anyway (the firebox area).....so we can consider that the masonry industry has a good lobbying arm!

Regular mortar will do fine outside the fireplace for repointing, etc.

I understand how the conversation can be confusing, because the codes, manuals and instructions often contradict each other. The whole thing is a changing and evolving process. Up until a few years ago, your chimney would not have had to be lined at all. But these codes changes are not "recalls", in other words if "they" thought the old methods were going to burn your house down (like aluminum wiring), there would be an action alert.

A sweep, fireplace pro, or code official takes all their experience into account when inspecting and suggesting a solution for you.

If nothing else, I think we should pretty much debunk that issue of one pipe not needing to be insulated and another needing to be. Interesting idea about the condensation, BUT, it is my understanding that UL does not do extensive destructive tests on these chimney liner (other than perhaps some basic ones)......so I really doubt that would be a factor. The insulation may serve that purpose (of keeping the condensation down), but the reason it is required in certain installations is that the chimney is defective (not up to par or code) in terms of it's ability to withstand high temperatures. That's my understanding, anyway.

All in all, insulation does have all those pluses, less condensation, higher stack temp (better draft), more consistency and the extra margin of safety. In the case of an existing sound chimney of 13x13, the safety thing may be the least of the benefits (in other words, I really doubt high temp is gonna be a problem on the chimney and framing structure).

Remember that many class A *(metal) chimneys other the years were (and still are) air insulated, and many of those have 400 series liners, so the corrosion aspect does not make sense in that case either.

 

[AdamC]

Hi all,

Thanks again for all of the input. I greatly appreciate all of your time and the fact that this forum is available.

Adam

 

[gpcollen1]

Cut the heatilator unit yesterday to facilitate getting the liner in. What a bear that was, not so much to cut, but to bend. It is not just a piece of old flue that needs to be cut, but the verticcal pice is welded to a horizontal piece that makes the top shelf of the heatilator unit. So a couple of cuts with the sawzall, a few holes drilled, a horizontal cut, then some attempts at bending the metal, then some more, then some more....finally think I got it but need to finish it off and seal it up. Got the liner down the chimney - 13x13 is so nice and easy. Ill post a couple of pics when i get home so you can see...if I remember.

 

[elkimmeg]

Lot off confusion here 304 is the cheapest grade SS used in a liner #16 TI is a grade where a stronger alloy Titanium is blended in for strength and durability
My opinion the target limit one should seek a better grade is 321 ti thicker and stronger but maybe over kill for the money. You decide the cost benefits?

then there are the thickness considerations .05 thinnest .06 better and great above .06

to obtain full compliance of UL 1777 listing insulation is required without the insulation the liner is not listed.
The question then becomes is full compliance necessary? This is the part where interpretations are being discussed.


required by code is a full inspection report governed by NFPA guidelines as to what has to be checked and confirmed. NFPA 211 outlines the details of 3 levels of reporting

If the existing chimney complies to NFPA construction and condition guidelines, then The liner does not need to be UL 1777 compliance.

Age of the chimney structure may also be an issues ,older it is, than more chances it does not comply to current NFPA 211 guidelines in structure or condition

Most chimneys built from 1990 and never having a chimney, built correctly, have the best chance of modern NFPA compliance..

However a chimney built last year can be failed due to discovering refractor cement was not used in the fire box of at liner joints. B Another common deficiency is the fire fox bricks not being backed with solid concrete. but hollow. One can hear a hollow sound just by tapping the fire box side wall bricks. Another common fault is the linners are not supported properly in the throat area I have seen the entire 30' clay liners supported by 2 masonry nails in the bricks.. The most dangerous situation is in the 2/3 brick front facing fireplaces and not the floor to ceiling ones it seems that the space between the angle iron and the Brick facing never gets filled leaving a clear path to the framing members headers above. Unfortunately this is a common occurance. With a flash light. look up inside the fire box at the front of the opening do you see a void or not a solid parged area?


WEb and JP are both correct here. One can find enough discrepancies to fail an existing liner system even if it looks sound,if refractory cement was not used where required.

disclaimer most masons used common mortar in the firebox construction and liner joints A common practice that we mostly accept really not a big life safety issue till the mortar fails.

An inspector can also waiver the inspection report, if he feels the chimney is modern and and was used very little. I uses the 10 year old limit ,knowing I inspected all chimney originally within that time frame in my town..

One other issue All have said insulation promotes a better draft. This is true, no argument here from me. What I want to point out is the chimney location. If the chimney is an internal location, it is a lot easier to heat up your flue and obtain a decent draft the benefits of insulation will have less effect promoting draft. If the chimney is exposed on an outside wall location
naturally it is prone to more heat loss and insulation will prevent this. The benefits of establishing a good draft ,are enhanced by insulation in exposed chimneys

I hope this cleared up some of the confusion

if the liners have missing motar joints or are cracked then it is not compliant for that matter the crown cracked and missing bricks or motar. Deffecient fire box or deteriated fire box also i
grounds for failure.

 

[AdamC]

Hi all,

Thanks again for all of the input.

I decided to bite the bullet and insulate. It seemed silly not to spend the extra $300 on a $3K job for the sake of improved safety and performance. I also like the fact that I can tell my insurance company that it meets the most current codes.

Adam