# Help with hearth requirements for Insert (K value)

Posted By ecfinn, Sep 23, 2006 at 4:36 PM

Not open for further replies.
1. #1

### ecfinn New Member 2. ```NULL ```

Dec 12, 2005
219
1
Loc:
Ambler, PA
Hi everyone,

I'm looking to install an Avalon Rainier in my existing masonry fireplace and I'm having some trouble understanding what the requirements are for my hearth. I've currently got a tile hearth, but it'll be redone and I need to understand what this statement means in the manual.

"Must be non-combustible 1/4" thick insulating board with a thermal conductivity of K = 0.72"

So I'm assuming I've got some type of sub-floor but I won't know until I tear up the tiles. I'm waiting to do that until I've planned what I'm replacing it with. So, can someone explain to me in laymans terms what this means for me? Do I need to put Micore and then Durock then tile? Can I put down a layer of stone of some kind as my hearth and be ok?

Thanks,
Eric Finn

2. #2

May 1, 2006
118
0
3. #3

### KP Matt New Member 2. ```NULL ```

May 1, 2006
118
0
Also, from another stove manual:

If k-value is given with a required thickness (t) in
inches: R=1/k X T

Which gives an R value of just under 0.35; a half inch sheet of Durock has an R value of 0.26.

One thing that puzzles me is the K value expressed with the inches sign after it.

4. #4

### elkimmeg Guest 2. ```NULL ```

K.72 = approx R1.4 little less maybe 1.39

5. #5

### KP Matt New Member 2. ```NULL ```

May 1, 2006
118
0
1.39 is four times 0.35; the manual calls for 1/4"... again, I'm confused by the 0.72" reference in the original post.

I thought K factor implies "per inch," whereas R value doesn't need to be expressed in inches?

6. #6

### babalu87 New Member 2. ```NULL ```

Nov 23, 2005
1,440
2
Loc:
middleborough, ma.
R and K values are related but not the same

I studied up on it pretty hard when I was designing my hearth pad.

This sums it up pretty well
https://www.hearth.com/articles/64_0_1_0_M1.html

Micore gives you the R and cement board gives the K

7. #7

### seaken Minister of Fire 2. ```NULL ```

Nov 21, 2005
580
5
Loc:
Shokan, NY
Good luck. Even Avalon doesn't understand it. I went around with them on this very statement when I had a local inspector who was insistant. Anyway, the final answer from Avalon was that any non-combustibel surface was acceptable. That statement does not seem to agree and I suggested they re-print the manual to clarify. So far, they haven't made the change. I'll post a couple of files that may help. Then I'm going to create a website that I can point to that may help do it yourselfers and industry installers make sense of this stuff.

8. #8

### seaken Minister of Fire 2. ```NULL ```

Nov 21, 2005
580
5
Loc:
Shokan, NY
Here's a couple of pages from my worksheet on R-value. They relate precisely to your Avalon Rainier question. It's all I have time for, for now.

Oops. Can't attach PDF files.

Send me a PM with your e-mail and I will e-mail the files.

9. #9

### seaken Minister of Fire 2. ```NULL ```

Nov 21, 2005
580
5
Loc:
Shokan, NY
The " mark at the end is not an inches mark but a quote mark.

And yes, K-factor is expressed PER INCH.

If K=0.72
Then R=1.39 for ONE INCH
and R=0.35 at 1/4"

If you achieve R=0.35 your hearth will meet the requirements of the statement in the manaul. Although, as stated, Avalon says you only need any noncombustible. I think you will better off going for the R=0.35.

10. #10

### ecfinn New Member 2. ```NULL ```

Dec 12, 2005
219
1
Loc:
Ambler, PA
So it looks like one layer of wonderboard and a layer of ceramic tile will satisfy the R-value requirements, if I'm reading the chart correctly. Thanks everyone for your help. Now all I need to do is finalize my plans and start the building process.

Eric

P.S. Sean I've sent you a PM as you requested.