Hearth Extensions and Wall Shields

A hearth extension must be installed with all fireplaces. It is to protect the floor in front of the fireplace from both radiant heat and sparks. For Model EST-48, the hearth extension must extend 12" beyond both sides and must extend 20" beyond the front. Use a durable noncom- bustible material having an equal or greater insulating value of k = .84 BTU IN/FT2 HR ° F or a thermal resistance that equals or exceed r = 1.19 HR ° F FT2/BTU IN. A minimum 1" thick noncombustible material is all that is required over a noncombustible slab floor.

Note: Any noncombustible material whose 1" k value is less than .84 or whose r value is more than 1.19 is acceptable.

If the fireplace is installed on a combustible floor, the metal safety strips (provided) must be used on the floor extending half under the fireplace and half under the hearth extension.

Secure the hearth extension to the floor to prevent possible shifting.

If the fireplace is installed diagonally across a 90° corner, the 24" sidewall clearance can be reduced to 20" and no wall protection is re- quired.

Side Wall cannot be Closer than 24" under any Circumastances

C

B

C A

Figure 44

C B C

A

D

Figure 45

16

Hearth Extension Dimensions

(For Figures 44 and 45 )

A20"

B48"

C12"

D72"

Methods of Determining Hearth Extension Equivalents

To determine the thickness required for any desired material when either the k or r values are known:

TM = thickness of desired material in inches kM = k value of desired material

rM = r value of desired material T1 = minimum listed thickness

Example: Micore CV230 is to be used with the EST-48 fireplace. How thick must this material be?

Using the k formula:

Desired

k value of desired

Min.Thickness

Required =

material (per inch) x

of listed

Thickness

k value of listed

 

material

 

material (per inch)

 

TM (inches) = kM x T1

.84

TM (inches) = 0.43* x 1" **

.84

Answer using k = 0.51 x 1 = 0.51 = ¹⁄₂"

Using the r formula:

Desired

k value of desired

Min.Thickness

Required =

material (per inch) x

of listed

Thickness

k value of listed

 

material

 

material (per inch)

 

TM (inches) =

1.19

 

x

T1

 

rM

 

 

 

 

 

 

TM (inches) =

1.19

 

x

1" **

 

2.33*

 

 

Answer using r = 0.51 x 1" = 0.51 = ¹⁄₂"

*value taken from chart

**minimum thickness per listing

NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.

Alternative Hearth Extension

and Wall Shield Materials

Listed

Values

Min. Thick

 

 

 

 

Material

k

r

TL

 

 

 

 

Millboard

.84

1.19

1"

 

 

 

 

Alternative

Values

Min. Thick

 

 

 

 

Materials

k

r

TM

Wonderboard

1.92

0.56

2 ³⁄₈"

 

 

 

 

Common brick

5.00

0.20

6"

 

 

 

 

Cement mortar

5.00

0.20

6"

 

 

 

 

Ceramic tile

12.5

0.08

15"

 

 

 

 

Marble

11.0

0.09

13"

 

 

 

 

Micore CV230

0.43

2.33

¹⁄₂"

(U.S. Gypsum)

 

 

 

 

 

 

 

Ceraform 126

0.27

3.70

¹⁄₂"

(Johns-Manville)

 

 

 

 

 

 

 

At times, it is important to know what combinations of materials are acceptable for use as hearth extension. The “R” values are used to determine acceptable combinations of materials because “R” values are additive where r and k values are not.

“R” value = 1 = r x thickness of material k

Example: Given that the required “R” value for a suitable hearth extension used with the EST-48 must be equal to or greater than “R” = r x T1 =

1.19x 1" = 1.19. It is desired to elevate a marble hearth extension to a level of 5” or more off the floor surface. What combination of noncom- bustible materials can be used to accomplish this?

If common brick is used so that the 3 ¹⁄₂" dimension is the height, then “R” for the common brick becomes:

“R”M = r x TM = 0.20 x 3 ¹⁄₂" = 0.70

Using ¹⁄₂" of mortar to set the brick, then “R” for the mortar becomes:

“R” = r x TM = 0.20 x ¹⁄₂" = 0.10

A ³⁄₄" marble slab set on ¹⁄₄" micore covers the brick, then “R” for the marble and micore becomes:

“R” = r x TM = 0.09 x ³⁄₄" = 0.068 “R” = r x TM = 2.33 x ¹⁄₄" = 0.5825