Hearth Floor Protection for Jotul Oslo...What r-value?

[80s Burnout]

I am building a hearth and the Oslo manual is not clear on the required r-value for the floor protection. Any of you Oslo folks know what that value is? In order for me to get my permit, the building inspector will hold me to the mfg. requirements. Clearances to walls and ceilings are clear.

As of right now I am planning on a 2 - 1/2" sheets of Durock and a layer of 1/2" vineer bricks. That's it. Two sheets of Durock should get me ~0.52 r-value and normal brick is about 0.80 r-value. With the vineers I'm probably 0.20 at most, maybe less. All-in I'm looking at about 0.72 r-value. Is that enough?

Thanks.
Burnout

 

[The Dali Lima]

I haven't looked at the manual yet, but it is available on their website:

(broken link removed to http://www.jotul.com/en-us/wwwjotulus/Main-menu/Products/Wood/Wood-stoves/Jotul-F-500-Oslo/)

By the way, anyone go to the Jotul site recently? Man, that crackling sound scares me every time! I keep thinking it is my laptop

 

[The Dali Lima]

Ok, I haven't read the entire thing, but here is the first section. No mention of R-value.

4.1 Floor Protection
Floor protection under the stove must be constructed of a noncombustible
material for protection from radiant heat, sparks,
and embers.
Individual sections of floor protection must be mortared
together to prevent sparks from falling through to combustible
materials. Any carpeting must be removed from under the floor
protection.
In the U.S. and Canada
The Jøtul F 500 must be installed on a non-combustible surface
extending:
A minimum of 18” (457mm) in front of the stove and the left side
load door (measured from the legs).
And 8” (200mm) on the right side and back of the stove (measured
from side and back panels).
This will result in a minimum floor protection of
54,25”W X 50,5”D.(1378mm x 1283mm) See figure 8.
In a rear vent installation the floor protection must also extend
under the stove pipe a minimum of 2” (50mm) beyond either
side of the pipe.

 

[The Dali Lima]

ok, so in the Appendix is states that an alternate material can be used if it meets certain requirements. Nowhere else in the manual does it mention floor protection requirements AT ALL.

Appendix A
Alternate Floor Protection
All floor protection materials must be non-combustible ie. metal,
brick, stone, mineral fiber boards). Any combustible material may
not be used.
The easiest means of determining if a proposed alternate floor
material meets requirements listed in this manual is to follow
this procedure.
R-value = thermal resistance
k-value = thermal conductivity
C-value = thermal conductance
1. Convert the specification to R-value;
a. If R-value is given, no conversion is needed.
b. If k-value is given with a required thickness (T) in inches:
R=1/k X T.
c. If C-value is given: R=1/C.
2. Determine the R-value of the proposed alternate floor
protector.
a. Use the formula in Step 1 to convert values not expressed
as “R”.
b. For multiple layers, add R-values of each layer to
determine overall R-value.
3. If the overall R-value of the system is greater than the R-value
of the specified floor protector, the alternate is acceptable.
Example:
The specified floor protector should be 3/4” thick material with a
k-factor of 0.84. The proposed alternate is 4” brick with a C-factor
of 1.25 over 1/8” mineral board with a k-factor of 0.29.
Step A. Use formula above to convert specifications
to R-value. R=1/k X T= 1/.84 X .75 = .893
Step B. Calculate R of proposed system.
4” brick of C-1.25, therefore
R brick = 1/C = 1/1.25 = 0.80.
1/8” mineral board of k = 0.29 therefore
R mineral board = 1/.29 X 0.125 = 0.431
Total R = R brick + R mineral board=
0.8 + 0.431=1.231
Step C. Compare proposed system R = 1.231 to specified R of 0.893.
Since R is greater than required, the system is acceptable.
Definitions:
Thermal conductance =
C = Btu = W
(hr)(ft2)(F) (m2)(K)
Thermal conductivity =
k = Btu = W = (Btu)
(hr)(ft2)(F) (m2)(K) (hr)(ft)(F)
Thermal resistance =
R = Btu = (m2)(K) = (Btu)(inch)
(hr)(ft2)(F) W (hr)(ft2)(F)
Alcoves require use of a bottom heat shield and hearth protection
having a minimum R-value of 1.6.



I'm interested in this as well... I was planning on ripping up the subfloor and installing Durock to my joists and then porcelan tile on the durock as my hearth... would that no be acceptable??

 

[80s Burnout]

Thanks guys - I saw this already, but it doesn't actually say what the r-value should be??? I'm heading to the building department now to see whether they will even check for that. Maybe all they look for are the hearth dimensions and clearance distances? I'll report back.

 

[80s Burnout]

Hold on....In that example it says " The specified floor protector should be 3/4" thick material with a k-factor of 0.84." But is that the actual requirement or is that an example??? Not very clear at all.

 

[The Dali Lima]

I think it was an example. It is VERY unclear.

 

[The Dali Lima]

I'll send an email to Jotul.

 

[firefighterjake]

I asked the same question when building my hearth . . . called the shop where I bought the stove and they contacted Jotul . . . their answer was that all you need is ember protection for the Jotul and that "this could even be sheet metal."

Needless to say I did go a bit more than just going for ember protection . . . I opted to go with a sheet of Durock (1/2 inch) covered by slate . . . it doesn't offer a lot of R value (the Durock, not the slate which offers little R value), but it does offer more than what is required according to Jotul.

 

[The Dali Lima]

I looked on their website and there is no email address... 8-/

Anyway, the manual does indicate in the beginning that the only requirement is ember protection. But at the end it goes into this complicated r-value formula. I'm going to contact my installer to be sure.

 

[80s Burnout]

Just spoke to my local building department and all they care about is meeting the clearance distance.....18" in front. Which is the only issue in my case. They even said there were some non-flammable rugs that would do the job.. Sounds sketchy to me. I'm still going with Durock and brick vineers.

 

[ansehnlich1]

My Oslo Manual says:

"Floor protection under the stove must be constructed of a non-combustible material for protection from radiant heat, sparks, and embers.

Individual sections of floor protection must be mortared together to prevent sparks from falling through to combustible materials. Any carpeting must be removed from under the floor protection."

For Alcove Installation: (in part)

"4. The bottom heatshield is required in all alcove installations."
"5. If a listed (UL/ULC) hearth board is not used the hearth that is constructed must have a minimum r value of 1.6 (see appendix a, page 19).

Our hearth is 4 layers of half inch durock then mortared brick laid flat on top, r-value approximately 1.8, not in an alcove.

I think the .8 r-value quoted above is for 4 inches of brick.

I can tell you when we have the Oslo crankin' the brick gets mighty warm underneath.

 

[firefighterjake]

Just spoke to my local building department and all they care about is meeting the clearance distance.....18" in front. Which is the only issue in my case. They even said there were some non-flammable rugs that would do the job.. Sounds sketchy to me. I'm still going with Durock and brick vineers.

I'm a firm believer in over-building things . . . going with Durock and the brick (mostly the Durock for the R value of course) in my own humble opinion would be a much better way of doing things (safer plus a better look).

 

[The Dali Lima]

Yeah, in re-reading the manual it appears that there is no requirement for r-value unless you are doing an alcove install. I guess that makes sense since there would be more heat build-up within the alcove.

We are building a 65x65 hearth that will be flush-set with the existing floor. I can probably get the 2 sheets of durock and a layer of porcelan tile if I gut the floor to the joists.