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Thread: Heat Shield

  1. #1
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    Default Heat Shield

    Don't see many of these in my area. What say you to the "heat shield"?

    (Any other comments or inspection tips are welcome).

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  2. #2
    Martin lehman's Avatar
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    Default Re: Heat Shield

    Mike, I'll tell you what I would do - I would defer that thing to a specialist without having a second thought.


  3. #3
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    Default Re: Heat Shield

    And while we at at it,: new to me: triangular chimney base. The door to the ash chute is behind the stuff piled against the chimney at left in the first picture, the second is a shot up through it. I think the rectangle at right may be an ash-dump for the fireplace in the pics above but I can't be sure as the firebox is sealed. But... what are those long thin rectangles... iron support angles?

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  4. #4
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    Default Re: Heat Shield

    Martin: NFK.

    Still, I try to understand.


  5. #5
    Martin lehman's Avatar
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    Default Re: Heat Shield

    Wow, that looks like a fun inspection!!

    You'll have to forgive me but what does NFK stand for?


  6. #6
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    Default Re: Heat Shield

    NFK = "No f*****g kidding".

    ___________

    Big house, 102 years old. It was a pre-listing inspection, only one today, and I took my time.... lots of it... it was just a really interesting place. Really regretted that I could not get to the chimney - steep roof, shingles shot, lots of loose granules - or get a look up from the FP. The cap and bricks are in bad shape, though, and if the seller gets someone out there before listing I'll try to meet them if I have time, it's about 10 min from my office.

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    Last edited by Michael Thomas; 07-23-2007 at 08:11 PM.

  7. #7
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    Default Re: Heat Shield

    A few more from this house - I really think this humidifier bypass needs more support.

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  8. #8
    Martin lehman's Avatar
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    Default Re: Heat Shield

    Gotta love the home ownner/handyman specials. I hope you got paid well -- real well.


  9. #9
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    Default Re: Heat Shield

    I'd be more concerned about the lack of hearth protection.


  10. #10
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    Default Re: Heat Shield

    Neal, are you referring to the material, the dimensions, or both?


  11. #11
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    Cool Re: Heat Shield

    Glad to see everyone recognizes this installation as a problem in dire need of a Level II inspection.

    Here is a quick list from a glance at the pics:
    No insulative/ recognized floor protection directly under the stove
    No 18" perimeter of non-combustible floor protection around the stove
    No 18" non-comb. past the loading door on the side
    No access into the throat/ chamber/ chimney for inspection or sweeping
    Need 36" clearance to combustibles off the stove (mantel, chest, wall, etc.)
    Chimney appears too short above roofline( 3/2/10 rule)
    Needs not just repointing but probably rebuilding
    No listed liner for the woodstove
    Concrete crown needs to be torn off and rebuilt.
    The center flue if fireclay (buff) while the side two are round vitreous clay. Possibly somebody has replaced that middle flue tile once before.
    Those cracks in the concrete crown and brick work could have been caused by thermal expansion from severe chimney fires, esp. if those round flues were mortared in.
    How does that stovepipe tie in to the chimney?

    If you were to pull that stove, the wood floor would probably be charred. Those firebrick appear to be soapstone. If you don't see a rating plate on the back stating it is listed to UL 1482, then treat it as unlisted per NFPA 211.

    So, what do ya'll think about that hearth construction? Thick enough? What is all that rebar doing? Clearance to the cleanout door?

    what a mess! Good pickup Michael.
    bob

    Keep the fire in the fireplace.

  12. #12
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    Default Re: Heat Shield

    This FP stuff really worries me - that does not look like a homeowner install to me. This is the first of these I've ever encountered in my area, but even I know (from just my reading and Dale Feb's one day class) there are so many things wrong there.

    Don't know enough to ID the material under the stove, but it was no more than 1/4" thick, with a pebbled, metallic surface. The chimney height is a bit deceptive in that picture, here's all I have from the other side, shot from the street - no room to get a ladder up on this side.

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    Last edited by Michael Thomas; 07-24-2007 at 08:23 AM.

  13. #13
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    Default Re: Heat Shield

    Bob, could you expand a bit on "listed liner for the woodstove"?

    Thanks


  14. #14
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    Smile Listed chimney liners

    Chimney liners come in all sorts of categories and uses. You can classify them by fuel category such as wood, coal, gas, oil, or pellet stove. You can also differentiate them by metallic versus cementitious/ pumped/ cast liners. Within metallic liners, you have flexible hose or rigid. Within those you can have round, oval, square or rectilinear shapes. Some liners require special insulation while others it is not required but often recommended by the liner mfr.

    The major model building codes use very similar language when addressing liners: Install a listed liner appropriate for the class of service and install it in accordance with the manufacturer's listed instructions. Therefore, installing unlisted liners is a code violation and therefore against the law in much of the country. Yet unlisted liners are growing. You can buy the machine to "roll your own" on site. Let's run through these categories briefly:

    Liners for wood are required to meet UL 1777 under the 2,100F test. You can test with a 1" airspace btw liner and chimney flue or in contact (zero clearance to the liner). Then you can have a 1" clearance btw the outside of the brick chimney to combustibles or zero clearance. The difference in clearances is primarily a function of insulation. A zero clearance requires the most insulation while the 1" is much less. For instance, most liners require one wrap of #8lb density 1/2" thick foil backed ceramic fiber insulation blanket for a 1" clearance to the outside and two wraps of this same insulation for a zero clearance. Most liners offer as an alternative, a cementitious insulation that is poured around the liner so there is at least 1" of this material btw liner and brick. Thermix is the most common however, some liner mfrs. have listed their liners with their own proprietary insulation so you must use their brand and not Thermix. Same with the blankets. Can't substitute.

    Ok, wood requires a 2,100F liner. Gas only has to meet UL 441 (same std for B-vent), which can handle a maximum of 550F or 400F above room temp. Type L vent is listed to UL 641 and was intended for oil. L vent is tested to 570F continuous and 1,700F short term. Since L vent can withstand higher temps. and worse corrosive conditions than B-vent, most L-venting is also approved for gas but not the other way around. Now, just to confuse you more, if you want your liner to handle gas and oil in addition to wood, you don't have to list it to UL 441 or UL 641 respectively. The same UL 1777 listing for wood also covers gas and oil by default. BTW, when I say gas, I'm only talking about Cat. I gas which is naturally vented non-positive flue gas pressure non-condensing and not less than a 17% flue loss (no higher than 83% AFUE). Cat. III appliances such as tankless water heaters use AL29-4C special venting which can be positive flue gas pressure but on the border as far as condensing. Cat. IV appliance venting must be listed to UL1738, which is a positive flue gas pressure and high corrosion environment. Note, you cannot vent a high efficiency Cat. IV appliance with a liner unless it also was listed to UL 1738.

    So, what about cast/ pumped liners? They specify the amt. of their proprietary cementitious mix that must be applied using their very specific methods. The German system (Ahrens) uses a vibrating bell to force a zero slump mix into place a min. 1.5" thick leaving the lumen of the flue, which is later coated with a glaze set. The English system uses bladders inflated to form the lumen of the flue then the cementitious mix is pumped in around it filling the voids. Once it has set, the bladder is deflated leaving the flue. There are several coating systems out there that claim to be tested or listed to portions of a UL std. I will ask Keving Stewart to comment on cast liners more as he is involved with a certain brand. He is limited as to what he can discuss as he is in court with a certain listing agency.

    The problem with roll your own liners and unlisted liners is a lack of predictability. Listed liners have been shown to meet a certain standard under extremely rigorous conditions. Once you gain a listing, you are subject to at least 4 un announced inspections by the listing agency. They can require you to produce the mill certificates showing you used the correct alloys of steel, check your records on gauging of equipment, check mfg. tolerances, etc. You can't do that with a machine in the back of a truck. For a company to sell liners that aren't listed tells you there must be something wrong with the liner that it cannot handle the test or the company cannot afford to pay for the testing.

    Now, since Cat.I gas appliances need only meet UL 441, the can be vented into aluminum liners. That doesn't make it a good idea but it is legal unless prohibited by the appliance mfr. or local ordinance. My problem with aluminum liners first is durability and second is corrosion resistance. I've seen many aluminum liners that were ripped apart, crushed or came unraveled during installation. Inexperience installers, esp. HVAC contractors, will often try to force the liner and damage it. Aluminum liners can easily crush to where there is insufficient venting capacity and much flue restriction. Where it makes the turn at the base, it often rips or crushes. However, AL liners installed down South will hold up much better than those herer up Nawth simply due to condensation. I recommend only stainless steel. Now, which alloy? The original stainless liner was Ventinox in 321 stainless, which is used on jet engine exhaust nozzles. However, it has shown some questions. Most liners for wood only are 304 or 304L stainless. Coal must be type 316 or AL 29-4C due to the severe corrosion. Oil is usually 316 or 316Ti (Titanium) or AL 29-4C. Cat.IV gas must be AL29-4C, which is super corrosion resistant. Unfortunately, high corrosion resistant alloys don't handle high heat as well as lower alloys without intergranular corrosion as chromium carbides are formed.

    So, when inspecting, can you tell which brand, alloy, or listing? Nope. With experience, you may be able to spot aluminum and even certain brands. I have learned to recognize some of the termination caps but the installers don't always use the liner mfrs.'s cap. For you guys, I would suggest you note somebody needs to provide proof the liner to the woodstove or fireplace is listed for wood and installed to the listing with the requisite insulation. When you find a rotten chimney that needs a liner, I suggest you recommend a reputable contractor and specify a listed liner suitable for that class of service and sized to the common vent requirements. In addition, you should recommend the installation be tested for draft, carbon monoxide spillage, and hopefully a full combustion analysis.

    Let me clarify not all HVAC techs don't know liners. Its just that recently a lot more have been getting into it and some shouldn't. Also, they often give away the liners as a "lost leader" in order to get the appliance replacement. Therefore, their prices are often will below market price from chimney contractors. Without violating Anti-Trust Guidelines, I suggest you call arond town and document what a typical liner goes for in your area. No offense but I get inspectors quoting 25 yr old pricing.

    Anyway Michael, that is the quick course on liners. If you are interested in more information, click on the FIRE Service banner and talk with the master, Dale Feb about training.
    HTH,
    Bob Harper

    Keep the fire in the fireplace.

  15. #15
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    Default Re: Heat Shield

    Bob,

    Thanks, as always, for taking time to reply.

    One question from up the thread:

    "Need 36" clearance to combustibles off the stove (mantel, chest, wall, etc.)"

    48" or 36"? - I was reviewing clearances for unlisted stoves in the CD drawings and found this:

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  16. #16
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    Smile Re: Heat Shield

    Michael, I quoted straight from NFPA 211. If there is a product listing, then the listing rules.

    -From Pawleys Island, SC visiting my brother, who is a Home Inspector,
    Bob

    Keep the fire in the fireplace.

  17. #17
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    Default Re: Heat Shield

    Bob,

    Thanks. Just wanted to make sure there was no exception I was not aware of.


  18. #18
    Dale W. Feb's Avatar
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    Default Re: Heat Shield

    Michael,

    The Uniform Mechanical Code requires a minimum 48 clearance to combustible material at top, back and sides and 54 clearance at front of an unlisted fireplace stove. You can reduce this clearance down to 36 when protection is provided as specified in Table 3-A. It is my belief that they simply wanted to eliminate unlisted fireplace stoves. This was there way without saying it. Pretty weak if you ask me. There is no evidence that 36 clearance is inadequate for safety. In fact, historically this number has performed very well. This same table has been used in all other codes and will allow the reduction of clearance down to 12 with the proper application of materials. The International codes now require that these stoves be listed, period. This is a straight forward approach.

    Fuel for thought


  19. #19
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    Default Re: Heat Shield

    Thanks. I'm determined to improve my understanding of fireplaces and stoves.


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