Thoughts on Fiberglass around SS liner

[offroadaudio]

I'm seeing low 20's for the next several days here, and the stove has a hard time keeping up at these temps.
I understand the advantages of a proper block off plate and insulation, but I need something that I can do quickly - the furnace is broken, so I could not keep things warm while I get the work done.
There is a sweep here that uses fiberglass regularly in the damper area, but I've heard negatives on the subject as well.
Before I decide to pull my surround and stuff some glass in, let's have the full-on debate here....

(this is a QF4100I in a masonry fireplace, with full 6" SS to top - nothing currently sealing damper area)

Thanks

 

[edthedawg]

ORA - do you have the fiberglass on hand already and that's why you want to do it quick and dirty? If you have access to a place like KAMCO, or a similar building supply place, get your hands on some mineral wool insulation and use that instead. I just got some for firesafing above my basement stairs (bathroom floor was up - it was wide open from attic to basement there) and at $60 for 40 sq ft x 4" thick, it was not that expensive. I know fiberglass shouldn't be a problem but I really fear its ability to withstand those temps directly at the flue pipe above the stove...

With "nothing" sealing the damper area - can you find ANYTHING to use as a blockoff plate? any piece of sheetmetal at all? an old car trunk lid?? anything?? I'd worry about that more than packing insulation up there, but I don't know what you have on hand, or how quick/cheap you need to get this done...

 

[offroadaudio]

Quick is better than cheap right now - if I could find mineral wool around here I'd spend the money, no problem.

 

[edthedawg]

Not sure where you are in PA - it's a big state (we vacation in Elysburg every summer) but if Lancaster is close, try these guys: http://www.iepindustrial.com/

 

[burntime]

Maybe cut some durock? Not sure but an idea.

 

[stejus]

I just had my insert installed in late December and the sweep left the damper area wide open with flex pipe running through it. The flex pipe runs all the way up and sealed at the top. I asked several about putting in some insulation in the damper and they all said fiberglass can be used because several sweeps do it. It's probably not the best solution but will work just the same. I went to Lowes and purchased a small bag of fiberglass for $3.50. It's about 2.5" thick. I stuffed it in the major gaps and as close to the pipe as possible. It's actually touching the pipe in some areas. I've had this insulation in since Saturday and no problems so far. There are still little gaps open but the big voids are closed up now. Next spring the whole clay liner flu is getting insulated.

 

[offroadaudio]

I just got a little break to do some research:

The basis of textile-grade glass fibers is silica, SiO2. In its pure form it exists as a polymer, (SiO2)n. It has no true melting point but softens at 2000°C, where it starts to degrade. At 1713°C, most of the molecules can move about freely. If the glass is then cooled quickly, they will be unable to form an ordered structure.[2] In the polymer, it forms SiO4 groups which are configured as a tetrahedron with the silicon atom at the center and four oxygen atoms at the corners. These atoms then form a network bonded at the corners by sharing the oxygen atoms.

2000 deg. C = 3632 deg F

I'm going with the fiberglass

 

[gpcollen1]

I DO NOT know this but I think the reason folks do not do it nor recommend it is that it is not code compliant.

 

[oconnor]

I once packed fibreglass around a double wall Selkirk chimney thimble that passed thru a concrete wall to air seal the gap - what I learned is that it will get hot enough to really stink up my house when it burns. That's why they make you use an attic insulation shield and they don't let you put it against the chimney in your attic.

Lots of folks use rockwool (aka mineral wool) as a "soft blockoff plate" and I haven't heard of any problems- I'm not a fan of that either, as I haven't seen anything to show me that rockwool has applications that approach the 2100*F that a liner is tested to for chimney fire reasons.

I have seen some rockwool products tested to a max sustained temp of 1200*F and 1400*F, but these aren't the stuff you get at the big box store - they are used for insulating boilers etc. I have seen as high as 1700*F from a European company that produced a rockwool based board type insulation - again, it fails the 2100*F for 60 mins test that the liner needs to pass.

There is a "heated" thread on here where I discussed the issue with a few folks - their point was that Roxul, for example, includes the fact that rockwool melts at 2150*F in their marketing material. Unfortunately, that number doesn't show up in thier spec sheets as a max operating temp for any of thier products, and I don't consider a marketing statement about the characteristics about a material to be a spec, especially when there are specs for items that are intended for use around flues to be tested at. That spec is the UL1777, and includes exposure to 2100*F for 60mins (Canadian test - the US test is similar at 2000*F I think).

The only thing I have seen that is rated for 2100*F is ceramic wool, AKA KAOWOOL. It is also tested in UL1777 situations. It is approved for use around liners.

So for me - fibreglass= no, rockwool = shouldn't and ceramic wool = sure.

That said, none of these are going to stop airflow, and that is what a blockoff plate is supposed to do. Just like stuffing fibreglass into the gaps around a window doesn't air seal the window very well (that is why we now use spray foam), a "soft plate" won't stop all the leakage. It will stop some, but not most of it.

Given the temp issues and lack of air stopping properties, I'd stick with steel.

If someone can find a spec sheet that shows me a fibreglass or rockwool listing for constant temp around 2100*F, then I'll buy off on fibreglass and rockwool around chimney liners. Until then the rockwool around my damper plate is coming out as soon as I get the time.

But, you can try this test first if you really want to know - wrap a foot of your flue pipe with fibreglass, wire it in place and light your stove. Heat it up, and see if you like the results. Get yourself some gloves, and a bucket with a cover though, as you may need them to take it all outside once the smell starts - I did.

 

[Rudyjr]

Many installers that I have spoken with in our area claim to use unfaced fiberglass with no issues. Others say they use rockwool with no issues. I have not encountered any that have any code compliance issues that that I know of. In the 70's and 80's everyone I know used unfaced fiberglass around single wall pipe to connect to existing chimney's. I myself had on installed in our home for about six years this way. When we moved I pulled the stove and pipe and the glass looked like it did when I put it in. I used rockwool insulation in the installation shown in my signature after speaking with local installers and building code people in my area.