6
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 (thermal
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
2. Determine the R-value of the proposed alternate floor
protector:
i. Use the formula in Step 1 to convert values not
expressed as R.
Clearance Requirements
After confirming that your fireplace is the right size, check
the clearance to combustibles. First mark with tape the exact
center of your fireplace opening on the hearth. Measure
the side clearance from this point. Measure the top trim
and/or mantel clearances from the finished hearth surface.
Measure the front clearance (to furnishings, etc.) from the
fireplace face. (Fig. 4)
X
FP1085
WinterWarm
clearances
3/01
C
A
B
Measure
side trim
clearance
from here
FP1085
Fireplace Clearances
A. Mantel*
43" (1092 mm)
B. Top Trim (1
1
⁄
2
")
41" (1041 mm)
C. Side Trim**
22
3
⁄
4
" (578 mm)
* Clearance shown is for 12" (305 mm) deep mantel. Dimension may
be reduced to 41" (1041 mm) if the mantel is 8" (203 mm) deep or less.
** Where side trim extends more than 1
1
⁄
2
" (38 mm) from the fireplace
facing, the side clearance must be no less than 31
1
⁄
4
" (794 mm); this
is also the required side wall clearance.
Measure the side clearance (C) from the exact center of your fireplace
opening on the hearth (X). Measure the top trim (B) and/or mantel
clearances (A) from the finished hearth surface. Measure the front
clearance (to furnishings, etc.) from the fireplace face.
Fig. 4
Observe these clearances to combustible trim.
Hearth Requirements
In some fireplaces, the hearth in front of the fireplace open
-
ing is brick, stone, slate, or some other non-combustible
material that is in direct contact with concrete poured over
earth. These are the only hearths that are considered
noncombustible. In other fireplaces, the brick or concrete
hearth in front of the fireplace opening is supported by
heavy wooden framing. Because neither brick nor concrete
has good insulating properties, heat radiated by the fire will
pass downward through the hearth to the wooden framing.
Such hearths are considered combustible.
The hearth for the Merrimack insert must be constructed
over a completely non-combustible surface (such as un-
painted concrete over earth). This non-combustible hearth
must extend at least 16" (406 mm) in front of the doors as
protection from heat radiated from the insert. This means
the non-combustible hearth must extend 23" in front of the
fireplace face opening in a typical installation.
In addition, spark and ember protection is needed 8" (203
mm) to each side of the insert and in Canada, 18" in front
of the insert. The approved construction of this protection
is a minimum or 24 gauge galvanized sheet metal or equiv-
alent. Figure 5 shows the details of hearth requirements.
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"
(203 mm)
8"
(203 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 and the hearth must also be
1
1
⁄
2
" thick with k-factor of 0.61 (R = 1.63 or equivalent).
*In the US, if the insert is elevated 2
1
⁄
2
" (64 mm) or more, no thermal
or ember protection is necessary beyond 16" (406 mm).
R = x T
1
K x 12
R = x T
1
k
