Block off plate vs insulation

[maple1]

roxal with a thickness of 6" is r15

Are you sure? I was thinking it was R5/inch - so R30. That's kind of what post 18 implies also.

 

[yooper08]

Roxul is R4.2/inch.

The Safe'n'Sound is less dense than the R15 product (11 pounds lighter), which has the same dimensions. What that means in terms of R value, I'm not sure. More air gap within the product may mean higher r value but more air gap also allows for more air to pass through.

 

[rwhite]

To your question about Roxul breaking apart, it's easy to cut with a decent serrated knife (think bread knife, they'll typically have some of these hanging by the bags).

Safe'n'Sound doesn't have much in terms of thermal insulation, it's designed to be a fire retardant and sound barrier. I've never been able to find what it's R value is.

I found it somewhere at some point but it was like R4 per inch.

 

[jetsam]

Safe'n'sound is more dense, with a lower R value due to less air space between the fibers.

(broken link removed to http://www.roxul.com/stone+wool/overview/faq)

Not that it matters for this application.

R15 Roxul is made for 2x4 walls and is 3.5" thick, not 6. The bag is clearly labelled.

 

[yooper08]

Safe'n'sound is more dense, with a lower R value due to less air space between the fibers.

(broken link removed to http://www.roxul.com/stone+wool/overview/faq)

Not that it matters for this application.

R15 Roxul is made for 2x4 walls and is 3.5" thick, not 6. The bag is clearly labelled.

Density=mass/volume
Dsns = 37.49/25803 = 0.001453
Dcb@R15 = 48.91/30103 = 0.001625
Dcb@R30 = 40.57/31349 = 0.001249

Given the density, R15 with the same dimensions as the Safe'n'Sound would weigh 41.92 pounds vs the 37.49 the Safe'n'Sound weighs.

SNS actually ends up between R15 and R30 - interesting. Given that R30 and R15 are both rated at R4.2/in, draw your conclusions on R then. That is if all three are constructed with the same materials (I assume they are, haven't looked that deeply into it).

 

[rwhite]

Going back in my way-back machine I recall a post on forum where the fellow had an old bag of safe and sound. At that time it was labeled with an r- value. IIRC the density of comfort bar was 2.0lbs/sqft vs 2.5 for safe and sound. The r-value for S&S was less but not substantially. Maybe it was 4 vs 4.2? Both have the same fire rating and look the same so I would assume the density is the only issue. It certainly has to have some r value even though the website states 0. I always use the S&S as that's all my local stores carry.

 

[yooper08]

Right, if I convert those densities to cubic feet (used inches earlier - got lazy - I know, it's one extra step), they turn out to 2.5, 2.8, and 2.2 per ft^3 respectively. 2.5 matches up with their TDS for SNS. For CB, they just list all CB products in the TDS and say density is >2.0 as it clearly varies by product.

Checked out the MSDS on it just to see if I could glean anything from there as their website outlines the two materials they use for the mineral fiber. Even though I didn't expect to find too many details on material makeup as it's essentially a trade secret, what I did find is that across their products, mineral fiber (all that it's listed as) makes up anywhere between 94-99% and the remainder is a formaldehyde binder(1-6%). Didn't know before that they used formaldehyde, so I read some more to find out about off gassing. The binder will off gas above 390F with trace amounts of formaldehyde, most of it is CO, CO2, ammonia, and water. Perhaps even more reason to seal it up if you worry about that kind of thing.

 

[Elciteeve]

Would it make sense to intentionally cause that product to off gas and vacate / ventilate the room it's off gassing in to prevent future problems or is that something that will happen for the life of the product?

 

[yooper08]

In theory you could prevent future off gassing if you know that the entire piece of insulation has reached that temperature. In reality, it may off gas over a period of time as you bring the stove up to a normal operating temp for longer durations and you heat up more of the insulation to that point. This would be similar to breaking in a stove and the paint curing...the hotter your fires get the closer you get to curing it all and no more smell.

 

[jetsam]

Roxul's published specs put s&s at 2.5#/cf, and comfortbatt at ">2"#/cf. I can tell you from handling it that it's not much >2, or it'd be heavier than the s&s.

The batts weigh about the same for 60 SF of coverage because the denser one is half an inch thinner.

Roxul doesn't emit a smell even if you put a butane torch on it for an hour (though the torch does eventually erode a hole in it). . Not saying that there's no offgassing, but I can't smell it if there is.

A MAPP torch vaporizes Roxul fairly quickly. I don't know where the vapor goes, so maybe it breaks up into carbon and silicone and wafts peacefully away. If you read about me dying horribly of lung problems, then much for that theory.

(In other news, it's often fun to be me.)

 

[yooper08]

If I was able to get the same number that Roxul has for S&S (2.5 #/cf), then I believe my numbers for R15 and R30 are also accurate, which places S&S nearly exactly in the middle of the 3. Batt for batt, S&S weighs in at 3 pounds and R15 weighs in at 4. If both were 3" thick, the difference would be small, with R15 coming in at 3.5 pounds. OR, if S&S was 3.5" thick, it'd weigh 3.65 pounds.

I wouldn't expect a smell since the gasses released are CO (doesn't smell), CO2 (doesn't smell), water (doesn't smell unless you've done something to it), and ammonia, with traces of formaldehyde. But if you heated up an entire room insulated with the stuff, it could be problematic/irritating.

It would be fun to play with torches and burn various things and/or blow stuff up. Roxul does react with hydrofluoric acid, wonder what happens?

 

[yooper08]

Sterling, how'd the install go?

 

[SterlingSL]

Sterling, how'd the install go?

They spent half the day destroying saw blades and finally got two (maybe three) of the tubes cut out. Also cut a half circle out of the heatform metal near the exiting damper so the flue can fit through (see pics!)

Now my question for everyone: before I go about build the block off plate, I noticed that the heatform that is currently there has a void behind the metal you see in the picture. Apparently it was a heat capture device as there is another plate behind that which forms a cavity ALL the way around the back and sides. Should I stuff some Roxul in that cavity? It would be similar to doing a Durock/Roxul insualtion except I already have a nice cavity there to stuff full! If yes, got any ideas how I can get the Roxul inside and around to the edges? The part where I will be stuffing it in is the half circle (see pics)

Thanks for the advice guys!

 

[DBoon]

FWIW, I've also been wondering about the R-value of the 3" Safe'N'Sound and I found a reference to an R-11 rating in this greenbuildingtalk.com forum post http://www.greenbuildingtalk.com/Forums/tabid/53/aff/12/aft/82894/afv/topic/afpg/1/Default.aspx

 

[Hogwildz]

Install a block off and insulated the top of the block off if you want, and call it done. The existing vents will still convect some heat if you leave the cavity alone. If anything, block off both holes through the old firebox, and the vents will work as they used to to a degree.

 

[SterlingSL]

The BOP will actually be below the remaining tubes. The Roxul will then surround the remaining tubes and go up the existing damper a ways (probably to the point where you last see the liner in that last pic).

I had thoughts that stuffing the existing heatform with insulation may be a waste of time as it will be trapped air once I seal off the top. Trapped air is a form of insulation in and of itself.

 

[Hogwildz]

I'm talking about the cavity between the two prior firebox shells. The 4 vents on the brick face are passive convection vents. Cold air enters through bottom vents, and exits through top vents as heated air. They use the heat from the cavity between the shells. Unless you plate off the top shell cut, insulation will not completely stop air flow up the existing flue. Fiber insulation does not stop air flow, and the more you pack it, the less it insulates.

I have a similar old fireplace, with no tubes up top, but dual shells and the 4 bricks vents. I installed a block off plate on the inner shell, with insulation on top of the block off plate, and called it done. Performs just fine. My insert has the steel firebox and an outer casing/shell around back, sides & top of the insert, not sure if your insert has an outer casing or not.

There are those that decide to insulate all around the insert, and while I understand the reasoning, especially with outside wall fireplaces, the I don't see a need for it as the insert I have has the outer shell.

 

[SterlingSL]

Plating off the the top shell cut is going to be next to impossible. So like you did I'm going to plate off the inner shell with Roxul filling the cavity above that.

One thing they did do was completely seal off the top of my chimney with mortar surrounding the cap. That will at least stop active air movement up and out.

 

[Squisher]

There are those that decide to insulate all around the insert, and while I understand the reasoning, especially with outside wall fireplaces, the I don't see a need for it as the insert I have has the outer shell.

I think the thought behind that is if there was room outside of the outer shell that it would be good to insulate around it on an exterior chimney. The outer shell on a PE certainly doesn't offer any insulation itself. If there was room on a exterior chimney install I can see the logic of insulating around the insert, or the outer shell on a PE.

OP, nice to see the progress. Good luck with it. Was insulating the liner discussed at all? Curious your installers thoughts on it? I would assume that some time/effort was made in verifying the clearance to combustibles on the existing chimney?

 

[SterlingSL]

OP, nice to see the progress. Good luck with it. Was insulating the liner discussed at all? Curious your installers thoughts on it? I would assume that some time/effort was made in verifying the clearance to combustibles on the existing chimney?

I asked about using an insulated liner vs. what they brought. He said they would have to go buy some insulation and wrap it. I've peered down my chimney on multiple occasions, including the day they were putting in the liner. It's nothing but solid brick and mortar. There is nothing combustible down there and I kind of got the "are you a moron" look from the sweep when I was asking about it.

 

[Squisher]

It's the clearances from the outside of the chimney to combustibles. Not inside the chimney. Interior(as in inside of the home)chimney needs 2" clearance to combustibles, exterior(chimney on an exterior wall where the backside is outside of the home) needs 1". What this means is if anywhere along the outside of your chimney combustibles are in contact with it, then this install doesn't bring an out of code chimney up to code. When the liner is insulated it negates all of those clearance concerns and allows for combustibles to be in contact with the outside of your chimney.

No sweep should be looking at you like a moron if you ask about insulating a liner. They should know what I just typed out and be able to explain to you why a insulated liner isn't needed. As in show you that you have the existing required clearances.

If there was room for insulation, espescially without having to bust out the liners it would have been well worth it to insulate the liner for safety and performance.

 

[Hogwildz]

If the old chimney is only brick, then you must insulate the new liner. To go without insulation, it would have had to have a clay liner in good condition, and still meet clearance to combustibles on whatever surrounds the chimney outer perimeter. Your installer should have known this, may have known this, but didn't want to go to the extra effort to install the insulation. Just my opinion, but regardless of location and clay liner or not, any new liner should be insulated. More protection & better draft are always a good thing.

 

[SterlingSL]

Maybe I'll tell them my insurance co. is demanding an insulated liner. Can't argue with that right?

 

[Hogwildz]

Maybe I'll tell them my insurance co. is demanding an insulated liner. Can't argue with that right?

You're the customer, you want what you want. You will have to pay the extra for the insulation, but it is worth every cent. You want full insulated from top to at least the smoke shelf. Don't let them talk you into stuffing insulation around the top and bottom. Full insulation wrap, period.

You could go as far as asking your insurance co. to send you a letter on their letterhead advising of required insulation.

 

[Squisher]

Maybe I'll tell them my insurance co. is demanding an insulated liner. Can't argue with that right?

I would stick with the truth if it's you that's demanding it. Or seek to get a letter like Hogwildz mentioned.

But I didn't see any info really on your chimney? Is it possible to confirm its integrity and clearances or not?

No one I suspect is going to be very happy once you tell them you want work redone, espescially if insulation or clearances were never even discussed and when you brought it up already was just brushed off. It could really change the scope of the work.