Monessen Hearth WOODBURNING FIREPLACE 424WBST User manual



For use in U.S./Canada
Underwriter's Laboratories
Report No. MH7603

87D1506 12/09 Rev. 2
Homeowner's Installation
and Operating Manual

342COVER

2
424WBST Designer Woodburning Fireplaces
87D1506


Read all instructions and warnings carefully before starting installation. Failure to
follow these instructions may result in a possible fire hazard and will void the warranty.

The 424WBST fireplaces are multi-side solid fuel, wood-
burning fireplaces. These are radiant models only and
include a preinstalled outside air kit.

Monessen Fireplaces and component parts have been
highly tested and will operate safely when installed in
accordance with instructions provided in this manual.
Carefully read and understand all instructions 
beginning installation.
If you notice any damage to fireplace or component parts,
immediately report damage to your Monessen Fireplaces
dealer.
Only use MHSC components or the warranty will be
voided and a fire hazard may be created.
MHSC warranty will be voided by and MHSC disclaims
any responsibility for the following actions:
• 

• 

• 



• 

• 







Consult local building codes to ensure that you are in
compliance installing the fireplace.
Fireplaces must be vented to the out-of-doors.







Fuels used in gas, wood-
burning or oil fired appliances, and the products of
combustion of such fuels, contain chemicals known to
the State of California to cause cancer, birth defects
and other reproductive harm.
California Health & Safety Code Sec. 25249.6




The fireplace should not be located in areas that create
drafts (ie: frequently opened doors and central heating air
inlets/outlets) that hamper the normal flow of air into the
fire.

If you plan to install a gas log, the gas line should be
installed  framing the fireplace. The gas line must
be installed by a certified gas line installer.




Safety Information . . . . . . . . . . . . . . . . . . 2
Specifications and Framing . . . . . . . . . . 3
Parts Identification . . . . . . . . . . . . . . . . . 4
Chimney Requirements . . . . . . . . . . . . . 6
Planning Information . . . . . . . . . . . . . . . . 7
Installation ....................... 8
Replacement Parts . . . . . . . . . . . . . . . . 20
Accessories .....................22


3
424WBST Designer Woodburning Fireplaces
87D1506

424WBST specifications and framing.
12”
(305 mm)
956O”
(241 mm)
49(6”
(1267 mm)
36"
(914 mm)
Gas Line Access
FP702A
STR SPECS
9/24/98
added note 9/21/99
3/09
Outside Air
146”
(372 mm)
20”
(508 mm)
12" (305 mm)
11” (279 mm ) Dia.
C
L
24" Total
Unit Width
Framing Width
Will be 24" Minus
2 x (Drywall Thickness)
1856M”
(464 mm)
STR33 STR36 STR42
A33" 36" 42"
838mm 914mm 1067mm
B37" 40" 46"
940mm 1016mm 1168mm
C1856O" 20" 23"
470mm 508mm 584mm
D49(6" 49(6" 53(6"
1267mm 1267mm 1368mm
E526M" 526M" 566M"
1340mm 1340mm 1442mm
F11" 11" 1356O"
279mm 279mm 343mm
G8" 8" 11"
203mm 203mm 279mm
J266M"  29 6QE"356QE"
680mm 741mm 894mm
8” (203 mm ) Dia.
12”
(305 mm)
526M”
(1340 mm)
36” (914 mm)
40” (1016 mm)
296QE” (741 mm)
756O”
(191 mm)
21”
(533 mm)
37”
(940 mm)
756O”
(191 mm)

4
424WBST Designer Woodburning Fireplaces
87D1506
FP701a

424WBST Parts Identification.
AB
FP1545
hearth dimensions
1/05
 
   
424WBST 29" 17Z\,"
(737 mm) (435 mm)
FP1545
 Hearth dimensions.
FP701a
STR Parts ID
Gas Line
Access
Outer
Dome
Outside Air
Access
Ledge Brackets
Header Standoffs
Flue Damper Control
(Inside)
Flue Collar
Outer Collar
Gas Line Knock-out
(Both Sides)
Brick liner on
Sides and Hearth
Air Inlet
Hearth
Wood Grate
Firebox
Metal Safety Strips,
shown not in place
(1, 2, or 3 Pieces)
Outside Air
Control

5
424WBST Designer Woodburning Fireplaces
87D1506

Insulation methods shown are optional
for cold climate, not a requirement for
unit operation.
FP704
 Fireplace and chase parts identification.
FP704
STR (from FP528)
7/28/98
Termination Cap
Storm Collar
Pan Flashing
Draftstop
Finish Wall
Batt Insulation
(cut out around
firestop)
Firestop
Ceiling Level
Outer Dome
Refer to Figures 21
and 26 for clearance
information.
Ledge Brackets
Nailing Flange
Gas Access
(both sides)
Outside Air Cover Plate
Surround
Screen
Grate
Firebox
Outside Air
Control

6
424WBST Designer Woodburning Fireplaces
87D1506

0 0 0 0 0 3" 11"
1 0 0 0 0 8Z\₄" 20"
0 1 0 0 0 11Z\₄" 25Z\₄"
2 0 0 0 0 13Z\₂" 29Z\₄"
1 1 0 0 0 16Z\₂" 34Z\₄"
0 0 1 0 0 20Z\₄" 40³\₄"
2 1 0 0 0 21³\₄" 43Z\₂"
0 0 0 1 0 26Z\₄" 51Z\₄"
0 1 1 0 0 28Z\₂" 55Z\₄"
1 0 0 1 0 31Z\₂" 60Z\₄”
0 1 0 1 0 34Z\₂" 65Z\₂"
0 0 2 0 0 37Z\₂" 70³\₄"
1 1 0 1 1 41Z\₂" 77³\₄"
0 0 1 1 1 45" 83³\₄"
0 1 2 0 1 47Z\₄" 87Z\₂"
0 0 0 2 1 51" 94"
0 1 1 1 1 53Z\₄" 98"
0 0 3 0 1 56Z\₄" 103Z\₄"
0 1 0 2 1 59Z\₄" 108Z\₂"
0 0 2 1 1 62Z\₄" 113Z\₂"
0 1 3 0 1 64Z\₂" 117Z\₂"
0 0 1 2 1 68Z\₄" 124"
0 1 2 1 1 70Z\₂" 128"
0 0 0 3 1 74Z\₄" 134Z\₂"
0 1 1 2 2 78" 140³\₄"
0 0 3 1 2 81" 146"
0 1 0 3 2 84" 151Z\₄"
0 0 2 2 2 87" 156Z\₂"
0 1 3 1 2 89Z\₄" 160Z\₄"
0 0 1 3 2 93" 166³\₄"
0 1 2 2 2 95Z\₄" 170³\₄"
0 0 0 4 2 99Z\₄" 177³\₄"
0 1 1 3 2 101Z\₄" 181³\₄"
0 0 3 2 2 104Z\₄" 186Z\₄"
0 1 0 4 2 107Z\₄" 191Z\₂"
0 0 2 3 2 110Z\₄" 196³\₄"
0 1 3 2 3 114" 203Z\₄"
0 0 1 4 3 117³\₄" 209³\₄"
0 1 2 3 3 120" 213Z\₂"
0 0 0 5 3 123³\₄" 220"

 ¹⁄₂ 
 
 
 G + H cannot exceed 20 feet.
Air Space Clearances:
SK8 (2-wall) = 1Z\₂"

The following safety rules apply to
offset installations (letters correspond
with illustration above):
 Height of the chimney is measured
from the hearth to the chimney exit.
424WBST
Maximum: 90'0"
Minimum:
Without Elbows 15'6"
With 2 Elbows* 17'6"
With 4 Elbows* 21' 0"
 Do not use more than 4 elbows per
chimney.
Attach the straps of the return (top)
elbow to a structural framing member.
The offset (first) elbow of any pair does
not have straps.
FP720
The chimney cannot be more than 30°
(45° in Canada) from the vertical plane in
any installation*.
The maximum length of the angled run
of the  chimney system is 20 feet. (G
plus H cannot exceed 20 feet.)
 A chimney support (Models TCS8A)
is required every 6 feet of angled run of
chimney. Chimney supports are required
for every 30 feet and 60 feet of vertical
chimney height above the hearth.
Determine the offset distance of your
chimney arrangement from the centerline
of the fireplace to the centerline of the
chimney where it is to pass through the
first ceiling.
 This offset distance may not be
your full offset distance. See Examples 2
and 3.
IWF282
MBUF
5/26/96
OFFSET
RISE
FP282
* In Canada, two (2) SK845 are allowed.
 Chimney system requirements.
D
RISE
BG
H
B
OFFSET
C
E
6 FT.
G
H
A
HEARTH
FLOOR
CHIMNEY
SECTION
CHIMNEY FLUE EXIT
ELBOW
FP720
STR/CVR
6/4/98
30˚
OFFSET
ELBOW
30˚
OFFSET
ELBOW
30˚
RETURN
ELBOW
30˚
RETURN
ELBOW
SKCS8
SUPPORT
Example 1 Example 2 Example 3

7
424WBST Designer Woodburning Fireplaces
87D1506

Preplanning an installation is very important to ensure
safety and to save time and money. An installer must
predetermine where a fireplace will be set and how the
chimney system will be run.
 The 424WBST model uses MHSC SK8 (2-wall)
chimney systems.

A fireplace may only be mounted on the following sur-
faces:
1. A flat combustible surface.
2. A raised wooden platform.
3. A concrete block or other solid object placed beneath
each of the four (4) corners of the fireplace.
The fireplace  be spaced 1/2" (13 mm) from a
combustible back wall and 1/2" (13 mm) from a com-
bustible side wall or support. (Page 14, Fig. 20)

Determine how the chimney will be run, length of run
and chimney components required to complete the
job. (Fig. 6)  install a chimney below minimum
heights.

Major U.S. building codes specify a minimum chimney
height above the roof top. The “Ten Foot Rule” is a fire
safety rule and not a draft rule. To ensure proper draft,
it is recommended that you always meet or exceed the
“Ten Foot Rule,” especially when installing a termination
on a high pitch roof. (Fig. 7)
The key points of the "Ten Foot Rule" are:
1. If the horizontal distance from the chimney to the
peak of the roof is 10' (3 m) or less, the top of the
chimney must be at least 2' (610 mm) above the
peak of the roof, but never less than 3' (914 mm)
in height above the highest point where it passes
through the roof.
2. If a horizontal distance from the chimney to the peak
of the roof is more than 10' (3 m), a chimney height
reference point is established on the surface of the
roof a distance of 10' (3 m) from the chimney in a
horizontal plane. The top of the chimney must be
at least 2' (610 mm) above the reference point, but
never less than 3' (914 mm) in height above the high-
est point where it passes through the roof.
In planning a chimney system, it is important to know:
1. The height of a chimney is measured from the
hearth to the exit point on the termination.
2. A chimney cannot be offset more than 30° from a
vertical plane.
3. A chimney may run straight up or it may be neces-
sary to offset it to avoid obstructions.
4. The maximum length of an angled run (total chimney
system) is 20' (6m).
5. No more than 2 offsets (4 total 30° elbows in U.S./or
2 total 45° elbows in Canada) per fireplace may be
used.
6. A guy wire stabilizer is required for chimneys extend-
ing more than 6' (1.8m) above a roof line.
 Installed lengths of chimney sections.
FP705
L1
L1
LTMODEL SK &
2 WALL CHIMNEY
TOTAL
LENGTH
(LT)
INSTALLED
LENGTH
(L1)
SK81
SK818
SK83
SK84
56O"
56O"
56O"
56O"
56O"
56O"
56O"
56O"
FP705
STR/CVR-CHIM SECT. INSTALLED LENGTH
5/28/98
AC246
 Ten Foot Rule illustration.
2' Min.
2' Min.
3'
Min.
0 To 10'
3'
Min.
0 To 10'
AC246
4/1/96
Reference
Point

8
424WBST Designer Woodburning Fireplaces
87D1506


If you live in a cold climate, it is not required but
 that you insulate fireplace
enclosure to eliminate cold air penetration as much
as possible.
Insulate base of fireplace with a non-combustible
insulation rated for a minimum of 300°F. Insulating
is  for outside wall installations over
a concrete slab. If fireplace is installed on a platform,
insulation should be placed on top of the platform
fireplace is set. (Fig. 9)
When a fireplace is installed in a chase or on a
outside wall, enclosure should be treated like any
outside wall in a home. Insulation should be installed
on the inside wall as well as the outside wall(s). In
a chase, it is also a good idea to install a firestop at
the first ceiling level above the fireplace and enclose
the chase with sheeting material. Insulation may
then be installed above sheeting material to assure
the space around the fireplace is totally protected.
(Fig. 4)
When installing the chimney,  caulk be-
tween outer pipe and firestop. It is vital that some air
be allowed to flow through this very thin gap.
 WHEN INSTALLING A FIREPLACE
IN AN INSULATED ENCLOSURE, BE SURE ALL
REQUIRED AIR SPACES ARE MAINTAINED. (Page
14, Fig. 20)


The chimney system is supported by the fireplace for
vertical chimney heights less than 20' (6 m) above the
hearth. Chimney supports are required if the vertical
height exceeds 20' (6 m). Locate chimney supports
at ceiling holes or other structural framing at 20' (6 m)
heights. Spacing between chimney supports 
exceed 20' (6 m). Use Chimney Support Model SKCS8
for SK8 chimney. 
 Support
provided by elbow straps fulfills the support require-
ment only if they are spaced as previously described. (A
chimney support is 2Z\₂" (64 mm) long when installed.)
Angled chimney runs require a support every 6' (1.8 m)
in addition to the elbow straps. Chimney supports are
used for this function. (Fig. 9)

A chase is a vertical box-like structure which encloses
the fireplace and/or chimney. Chases are typically built
on the outside of the house with fireplace opening cut
into the outer wall of a room. (Page 5, Fig. 4)
If you need help in determining fireplace location or
how the chimney system should be run, contact your
Monessen dealer for assistance.
FP284
 Chimney support installation
IWF284
MBUF
5/25/96
Chimney Sup-
port Strap
SKCS8

9
424WBST Designer Woodburning Fireplaces
87D1506

Framing can be constructed before or after the fireplace
is set in place, however, most installers build the frame
before setting the fireplace.
Frame fireplace with 2 x 4 lumber or heavier materi-
als. Refer to framing dimensions in Figures 1, 2, 3 or 4
for basic fireplace specifications. Headers and support
studs must be turned on end as illustrated on Page 5,
Figure 4.
 Framing should be positioned to accommodate
wall covering and fireplace facing material. 




FP706
 Insulating between platform and fireplace.
FP706
STR/CVR
6/1/98
Hard, Flat
Surface
Insulation
Plateform

Since you have already preplanned the chimney run,
you should know exactly how the installation is to
be accomplished — how much pipe is required, the
number of elbows, if any, and type of termination to be
used.
REPORT TO YOUR DEALERS ANY
PARTS DAMAGED IN SHIPMENT, SPECIFICALLY
CHECK THE END CONNECTION OF CHIMNEY SEC-
TIONS AND ELBOWS.
 The 424WBST model uses MHSC SK8 (2-wall)
chimney systems.

To locate the centerline of the flue put the fireplace in
final position and place a plumb bob from the ceiling to
the center of the fireplace flue collar. Mark this spot on
the ceiling. Draw a line through that mark to either side
of the firebox and indicate dimension X to locate the
side wall framing. (Fig. 10) Be sure to observe clear-
ance requirements for side and parallel combustible
walls as noted in Page 16, Figure 23.

In order to clear an obstruction, it may be necessary to
offset chimney from vertical. This is accomplished by
using MHSC elbows. Use the 30° Offset Elbow table on
Page 6 to determine proper offset and parts required.
Each offset requires two (2) elbows. The second elbow
is equipped with support straps. It is very important to
install the second elbow in each offset as close to the
ceiling or support as possible so that the elbow straps
can be secured to framing members to help support the
weight of the chimney.
Determine offset distance of your chimney arrangement
from centerline of fireplace to centerline of chimney
where it is to pass through ceiling.
Locate center point of the chimney on ceiling as though
a straight up chimney arrangement is to be used.
Measure your offset dimension from the chimney center
point on the ceiling.

10
424WBST Designer Woodburning Fireplaces
87D1506


The size of the hole in ceiling will vary with the angle at
which the chimney passes through ceiling.
Drive a nail up through ceiling at marked chimney cen-
ter point. Go to floor above and see where hole will be
cut. Check to see where existing ceiling joists and other
possible obstructions are located...i.e. wiring, plumbing
etc... If necessary, re-position chimney and/or fireplace
to avoid obstructions.

Cover fireplace collar opening and cut proper sized
chimney hole in chimney. The SK8 pipe allows you to
run pipe through a typical 16” on center joist without
cutting joists.

Frame the ceiling chimney hole as shown in Figure
12. It is good practice to use framing lumber that is the
same size as the ceiling joists; this is a requirement at
attic level.
The following table gives firestop spacer model num-
bers:
FP707
STR/CVR
LOCATE CENTER LINE
6/1/98
STR 33: 19" (483mm)
STR36 / CVR36: 205/O" 521mm)
STR42 / CVR42: 235/O" (597mm)
MODEL X =
2056O”
(521 mm)
 Locate centerline of chimney with plumb line.
FP707
Actual Centerpoint
Chimney
Centerline
Side of STR
Plumb Line
Plumb Bob
Imaginary
Centerpoint
 Typical frame for ceiling chimney hole.
FP551A
FP551A
BR/BC
9/23/98
1456O"1456O"
Existing
Ceiling
Joists
Chimney
Hole
New Framing
Members
 Ceiling chimney hole sizes necessary for installing
firestop spacer.

   
8" Flue SKFS2A SKFS6A
"SK" Series 14Z\₂" x 14Z\₂" 14Z\₂" x 25Z\₂"
(368 x 368 mm) (368 x 648 mm)
The  of the frame the same
as the hole size selected from Figure 12 in order to
provide the required air space (1Z/₂" (38 mm) with SK8
between the outside diameter of the chimney and the
edges of the framed ceiling hole.