7
Merrimack Large Insert
30004671
how to Determine if alternate Floor
protection Materials are acceptable
All floor protection must be noncombustible (i.e. met-
als, brick, stone, mineral fiber boards, etc.). Any organic
materials (i.e. plastics, wood paper products, etc.) are
combustible and must not be used. The floor protection
specified includes some form of thermal designation
such as R-value (thermal resistance) or k-factor (ther-
mal conductivity).
procedure:
1. Convert specifications to R-value:
i. R-value given - no conversion needed.
ii. k-factor is given with a required thickness (T) in
inches:
iii. K-factor is given with a required thickness (T) in
inches:
iv. r-factor is given with a required thickness (T) in
inches: R = r x T
. Determine the R-value of the proposed alternate
floor protector:
i. Use the formula in Step 1 to convert values not
expressed as R.
ii. For multiple layers, add R-values of each layer to
determine overall R-value.
FP2492
hearth protection
7/09 djt
A
C
B
B
7”
(178 mm)
United States
canada
A. 18”* (460 mm)
18” (460 mm)
B. 8”
(03 mm)
8”
(03 mm)
C. 46
¹\₂
” (1181 mm) 46
¹\₂
” (1181 mm)
FP1095
Fig. 5
Unless your fireplace and hearth are constructed over
a dirt floor (or unpainted concrete over dirt), you must use a
floor protector that satisfies the above requirements.
In all cases, the hearth must be completely noncombustible in front
of the insert to the dimensions shown. The hearth must also be
1
¹\₂
” thick with k-factor of 0.84.
*In the US, if the insert is elevated
¹\₂
” (64 mm) or more, no ther-
mal or ember protection is necessary beyond 16” (406 mm).
R = x T
1
K x 1
r = =
(ft
)(hr)(°F)
(Btu)(in)
1
k
(Btu)(ft)
(ft
)(hr)(°F)
K =
k = = K x 1
(Btu)(in)
(ft
)(hr)(°F)
R = (ft
)(hr)(°F)
Btu
R = x T
1
k
optional Surround packages
Custom-made surround panels may be made from any
noncombustible material.
MHSC offers a steel or cast iron surround panel kit.
3. If the overall R-value of the system is greater than
the R-value of the specified floor protector, the alter-
nate is acceptable.
eXaMpLe:
The specified floor protector should be 1
¹\₂
-
inch thick material with k-factor of 0.84. The proposed
alternate is 4” brick with an r-factor of 0. over 1/4”
mineral board with a k-factor of 0.9
Step a: Use formula above to convert specification to
R-value:
Step b: Calculate R of proposed system.
4” brick of r = 0., therefore:
R
brick
= 0. x 4 = 0.8
Step c: 1/8” mineral board of k = 0.9, therefore
R
mineralboard
= x 0.5 = 0.86
Step d: R
total
= R
brick
+ R
mineralboard
= 0.8 + 0.86 = 1.66
Step e: Compare proposed system Rtotal of 1.66 to
specified R of 1.79. Since proposed system Rtotal is
less than required, the system is not acceptable.
Definitions
R = x T = x 1.5 = 1.79
1
k
1
0.84
1
0.9
