Vermont Castings Merrimack User manual


30004671 3/11 Rev. 4


For Use in North America






Homeowner’s
Installation
and Operating
Manual
Nous recommandons que nos appareils de chauffage
au bois soient installés et entretenus apr des
professionnels qui ont été accrédités aux É.-U. par le
National Fireplace Institute® (NFI) comme étant des
spécialistes du NFI en matière d’appareilsde chauffage
au ois, ou qui sont accrédités au Canada
dans le cadre du Programme
de formation technique
en énergie du bois (WETT)
4671
Merrimack cover


Merrimack Large Insert
30004671















Specications ......................................................... 3
Installation .............................................................. 4
Operation ................................................................ 9
Maintenance ......................................................... 13
Optional Accessories ............................................ 16
Replacement Parts ............................................... 17
Warranty ............................................................... 19

 Fuels used in gas, wood-
burning or oil red appliances, and the products of
combustion of such fuels, contain chemicals known
to the State of California to cause cancer, birth de-
fects and other reproductive harm.
California Health & Safety Code Sec. 549.6
Thank you for purchasing a Vermont Castings Merrimack Large Insert, an efcient wood stove carefully engineered to
bring you the latest in wood combustion principles and modern foundry technology.
This stove transforms a traditional masonry replace into a powerful heater. You can count on years of comfortable
heating and pleasurable re-viewing if you operate and maintain it according to the directions in this Owner’s Guide.
This Insert has been tested and listed by OMNI-Test Laboratories of Portland, Oregon to ANSI/UL 148 for the United
States and ULC S68 for Canada. This Insert is listed to, and in compliance with, the standards set forth by the
Federal Environmental Protection Agency, 40 CFR Part 60.53(b), as stated on the permanent label attached to the
stove.
This manual describes the installation and operation of this Insert. This heater meets the U.S. Environmental Protec-
tion Agency’s emission limits for wood heaters sold after July 1, 1990. Under specic test conditions this heater has
been shown to deliver heat at a rate ranging from 10,750 to 31,780 BTU/hr.
For more complete details on stove performance and specications, please refer to Page 3.
The Merrimack Large Insert is designed, tested and listed for burning wood. Do not burn other fuels.
Installation or service of the Merrimack Large Insert should be performed only by a qualied installer, preferably NFI or
WETT (Canada) certied.
Please read entire manual before you install and use your new Insert.
Failure to follow these instructions may result in property damage, bodily injury or even death.

3
Merrimack Large Insert
30004671


EPA Emissions Rating .......................................3.6 g/hr
Range of heat output*.............. 10,750 - 31,780 BTU/hr
Maximum heat output** ..........................55,000 BTU/hr
Area heated*** ................................... up to ,000 sq. ft.
Size of wood splits .......................... up to ” (560 mm)
Fuel Capacity.......................................... 40 lbs. (18 kg)
Loading ..................................................................Front
Flue size .................................................... 6” (150 mm)
Fireplace Insert weight ....................... 480 lbs. (18 kg)
Primary Air Control ............................................ Manual
Glass panel.......................... High-temperature ceramic
Flue exit position...................................................... Top
Blower rating...............................150 cfm. (115V, 60Hz)
Power Cord Length................... 6 foot useable installed
*Under specic test conditions used during EPA emis-
sions standard testing.
**This value can vary depending on how the unit is
operated, and the type and moisture content of the fuel
used. The gure shown is based on maximum fuel con-
sumption obtained under laboratory conditions and with
average efciencies.
***These values are based on operation in building-
code conforming homes under typical winter climate
conditions in New England. If your home is of nonstan-
dard construction (e.g. unusually well insulated, not in-
sulated, built under ground, etc.) or if you live in a more
severe or more temperate climate, these gures may
not apply. Since so many variables affect performance,
consult your Vermont Castings’ Authorized Dealer to
determine realistic expectations for your home.
 Merrimack Large Insert dimensions.
2956” (740 mm)
246M” (629 mm)
126QE”
(313 mm)
266QE”
(668 mm)
17556QE” (449 mm)
2356QE”
(605 mm)
4671
Merrimack dims
76QE”
(183 mm)
3156O" (800 mm) 256” (645 mm)

4
Merrimack Large Insert
30004671
Installing the Merrimack Large Insert into an existing
masonry replace is an effective way to add an efcient
heater to your home. The existing replace and chim-
ney must meet certain requirements.

The Merrimack Large Insert is listed for installation
within a properly built masonry or heat circulating, ma-
sonry-type replace that is constructed in accordance
with the requirements of recognized building codes. A
heat-circulating masonry-type replace must conform
to building code standards for masonry replaces, and
must consist of a factory-built metal rebox with air
circulation pathways that are surrounded by masonry
materials. Air circulation pathways must not be blocked
by the insert or surround panels.
The replace and chimney must be clean and structur-
ally sound. Have them inspected by a qualied profes-
sional chimney sweep, a mason, or your Vermont Cast-
ings’ Authorized Dealer before the Merrimack Large
Insert is installed. Any deterioration (cracks, loose
mortar or loose bricks) must be repaired.
Codes may permit removal of the damper in order to
make a positive vent connection between the rebox
and the chimney. However, the replace should not be
modied in any way without rst checking with your lo-
cal building inspector or re marshal. Provision should
be made to restore the replace to its original condition
if the insert is removed. Do not remove bricks or mortar
that may jeopardize the compliance of the replace with
local building codes.




Chimney requirements differ for the U.S. and Canada.
Specications for each are listed below. Connect the
insert to the chimney in accordance with local codes
and the requirements of the listing agency as specied
in this manual.

Chimney height should be no less than 15’ (4.5 m)
above the hearth and no more than 35’ (10.5 m).
The chimney should extend at least 3’ (914 mm) above
the highest point where it passes through a roof, and at
least ’ (610 mm) higher than any portion of a building
within 10’ (3 m). (Fig. )



 

• A connector must extend from the ue collar
to the ue liner.
• The cross sectional area of the ue must be less
than or equal to three times the area of the ue
collar. If larger, the chimney must be re-lined.
• Means must be provided to prevent room air
passing to the chimney cavity.
• Provision must be made for removal of the
insert to clean the chimney ue.

• While not required in most jurisdictions in the
U.S., MHSC strongly recommends that a full
stainless steel chimney liner be installed for the
insert to the chimney top to increase overall per-
formance and to ease and reduce yearly mainte-
nance.
• A masonry chimney must be well-constructed
and must meet minimum code requirements.
The chimney ue should have a code-approved
liner made of masonry or pre-cast refractory
tiles, straight or exible stainless steel pipe, or a
poured-in-place liner. An unlined chimney must
be relined professionally.
• The chimney must have a nominal ue size of
6” (15 mm) diameter or 8 square inches (181
cm) but no greater than 3 times larger or 85
square inches (548 cm). A chimney larger than
this must be re-lined.
2' Min.
2' Min.
3'
Min.
0 To 10'
3'
Min.
0 To 10'
AC617
RLTSKC8
2/11/98
AC617
Reference
Point
 The ’-3’-10’ rule for chimneys.

5
Merrimack Large Insert
30004671
Be aware that a chimney originally designed for re-
place use may perform differently when used to vent an
air-controlled appliance such as your Merrimack Large
Insert - even if the ue is less than 3 times larger than
the ue collar. For example, a chimney on an outside
wall may not heat up enough to sustain an adequate
draft. Such a ue can often be improved if it is relined to
reduce its size and/or insulated to keep it warmer.
• A positive ue connection must be made between
the Insert and the rst masonry tile or prefabri-
cated metal chimney section. A positive ue con-
nection consists of a plate that seals or replaces
the replace damper and a section of chimney
connector that passes through the plate into the
chimney.
• The chimney connector must be a minimum
equivalent to a 6” (15 mm) diameter opening
and must be 4 gauge or heavier stainless steel.
Chimney Connection systems are available from a
variety of manufacturers. Your Vermont Castings dealer
can recommend a system that will best meet the re-
quirements of your particular installation.

• The chimney must be sealed off from room air,
either by a plate at the damper level or by sealing
the replace opening.
• Unused openings to the ue must be sealed with
masonry to the thickness of the chimney wall.
Openings sealed with pie plates or wallpaper are
a hazard. In the event of a chimney re, ames
and smoke may be forced from the openings.


• A full chimney liner meeting ULC S635, Class III
(stainless steel) must be installed from the insert
to the chimney top, and securely attached to
both. The damper may be removed to accommo-
date the liner.
• The opening of the replace around the insert
must be sealed to prevent room air passing to the
replace cavity.
• Existing air-circulation chambers in a replace
with a steel liner may not be blocked.
• Provision must be made for removal of the insert
to clean the chimney ue.
• The existing replace damper (if any) should be
locked in the open position.
• A permanent metal warning label must be afxed
to the back of the replace stating the replace
may have been altered to accommodate the in-
sert, and may be unsafe to use as a conventional
replace. (A Fireplace Modication Tag is in-
cluded in the hardware bag inside the Merrimack
Large Insert.)

The Merrimack Large Insert will t many replaces. To
conrm that it will t yours, measure the lintel depth,
plus the height, width, and depth of your replace and
hearth. Compare them to the measurements in the ac-
companying chart. If you choose to install a new hearth
over an existing replace hearth, be sure to take its
thickness into consideration when measuring both front
and back height of the replace and clearances to any
existing trims and mantels.
 The clearance between the Merrimack Large
Insert and the mantel, top trim and side trim cannot be
reduced by installing shields.
Another requirement to consider is the clearance for
movable items such as tables, bookcases, rugs, furnish-
ings, and your woodbox. All combustible materials of
this type should be a minimum of 48” (10 mm) from
the front surface of the Merrimack Large Insert. Be sure
that family members are aware of this requirement as
well, so they too will keep objects a safe distance from
the stove.

6
Merrimack Large Insert
30004671
A,I
BC
D,J
E
D,J
H
CE
FP1084
winterwarm
fireplace minimum dimensions
3/01

A. Width at Face 9C\v” (756 mm)
B. Width at Dimension ‘C’ 5” (635 mm)
C. Depth1 18¹\₂” (470 mm)
D. Height at Face 3C\v” (603 mm)
E. Height at Dimension ‘C’ 3C\v” (603 mm)

H. Lintel depth 9” (9 mm)
I. Width 45” (1143 mm)
J. Height 3” (813 mm)
FP1084
1. The minimum depth must be maintained from the oor of the replace
to a height of 1¹\₂” (540 mm)
. Though the Merrimack Large Insert will t into larger replaces, the
decorative optional MHSC Surround Panels will not completely cover the
replace opening if these dimensions are exceeded. Custom made trim
pieces may be used.
 Use these measurements to conrm that the Merrimack
Large Insert will t into your masonry replace.

After conrming that your replace is the right size,
check the clearance to combustibles. First mark with
tape the exact center of your replace opening on the
hearth. Measure the side clearance from this point.
Measure the top trim and/or mantel clearances from the
nished hearth surface. Measure the front clearance (to
furnishings, etc.) from the replace face. (Fig. 4)
X
FP1085
WinterWarm
clearances
3/01
C
A
B
Measure
side trim
clearance
from here
FP1085

A. Mantel* 43” (109 mm)
B. Top Trim (1¹\₂”) 41” (1041 mm)
C. Side Trim** C\v” (578 mm)
* Clearance shown is for 1” (305 mm) deep mantel. Dimension
may be reduced to 41” (1041 mm) if the mantel is 8” (03 mm)
deep or less.
** Where side trim extends more than 1 ¹\₂ ” (38 mm) from the re-
place facing, the side clearance must be no less than 31¹\v” (794
mm); this is also the required side wall clearance.
Measure the side clearance (C) from the exact center of your re-
place opening on the hearth (X). Measure the top trim (B) and/or
mantel clearances (A) from the nished hearth surface. Measure
the front clearance (to furnishings, etc.) from the replace face.
 Observe these clearances to combustible trim.

In some replaces, the hearth in front of the replace
opening is brick, stone, slate, or some other non-com-
bustible material that is in direct contact with concrete
poured over earth. These are the only hearths that are
considered noncombustible. In other replaces, the
brick or concrete hearth in front of the replace opening
is supported by heavy wooden framing. Because nei-
ther brick nor concrete has good insulating properties,
heat radiated by the re will pass downward through
the hearth to the wooden framing. Such hearths are
considered combustible.
The hearth for the Merrimack insert must be construct-
ed over a completely non-combustible surface (such as
unpainted 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
3” in front of the replace face opening in a typical
installation.
In addition, spark and ember protection is needed 8”
(03 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 4 gauge galvanized
sheet metal or equivalent. Figure 5 shows the details of
hearth requirements.

7
Merrimack Large Insert
30004671


All oor protection must be noncombustible (i.e. met-
als, brick, stone, mineral ber boards, etc.). Any organic
materials (i.e. plastics, wood paper products, etc.) are
combustible and must not be used. The oor protection
specied includes some form of thermal designation
such as R-value (thermal resistance) or k-factor (ther-
mal conductivity).

1. Convert specications 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
oor 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
BB
7”
(178 mm)
 
A. 18”* (460 mm) 18” (460 mm)
B. 8” (03 mm) 8” (03 mm)
C. 46¹\₂” (1181 mm) 46¹\₂” (1181 mm)
FP1095
 Unless your replace and hearth are constructed over
a dirt oor (or unpainted concrete over dirt), you must use a
oor protector that satises 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
1¹\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

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 specied oor protector, the alter-
nate is acceptable.
 The specied oor protector should be 1¹\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 specication to
R-value:
Step b: Calculate R of proposed system.
4” brick of r = 0., therefore:
Rbrick = 0. x 4 = 0.8
Step c: 1/8” mineral board of k = 0.9, therefore
Rmineralboard = x 0.5 = 0.86
Step d: Rtotal = Rbrick + Rmineralboard = 0.8 + 0.86 = 1.66
Step e: Compare proposed system Rtotal of 1.66 to
specied R of 1.79. Since proposed system Rtotal is
less than required, the system is not acceptable.
Denitions
R = x T = x 1.5 = 1.79
1
k
1
0.84
1
0.9

8
Merrimack Large Insert
30004671

 If codes al-
low, remove the damper. Many dampers can be removed
simply by removing a cotter pin and/or a set screw.
If it is not permissible or possible to remove the damper,
secure the damper in the fully open position.

      

 if you have modied the
replace in any way to accommodate installation of a
replace insert. This tag is in the hardware bag included
with your Insert.
  The ue collar may be oriented
in the vertical position or rotated 180 degrees on the top
of the stove resulting in a 6 degree backward angle. If
possible, determine beforehand which orientation will
work best for your application.
In most applications, cleaning of the chimney system will
be easiest from the top (chimney cap) down. If this is the
planned method for your application, the center iron pull
down handle on the ue collar serves as protection to
prevent a chimney brush from damaging the bafe inside
the stove. If cleaning can only take place from inside the
home, the center bar may be cut out of the ue collar using
a hack saw or reciprocating metal cutting saw.
3.  Again, depending on your
application it may be easiest to install the connector or
stainless steel ue liner in the chimney rst. Refer to
Figure 6 for the components of the venting system.
• Carefully remove the ber bafe by rst removing
the front air wash manifold. If necessary, remove the
air tubes to allow easier access.
• Remove the iron ue collar from the stove and fasten
either the adapter pipe or ue liner to it by drilling
three holes using the holes in the iron collar as a
guide.
• Secure the exible pipe to the pipe adaptor using
the same method.
• Install the connector pipe or liner so that the height
measured from the nished hearth surface to the
center bar of the ue collar is 0¹\₂” (51 mm). (Fig.
7) This will allow an easy connection once the stove
is rolled into place.
   Run the power cord
out the left or right side of the insert. Remove the two
() louvre doors (Fig. 9) or access doors. Remove the
screw and washer from each side holding the ashlip
to the front. If you run the power cord out the left side,
remove the two () screws holding the rheostat bracket
to the fan housing. Insert grommet nearest fan in the slot
on the fan housing, left or right side. Reattach rheostat
bracket with the two () screws removed earlier. Remove
the cover plate and insert the provided grommet into
the slot. Reattach the cover plate.
 Remove the prepack-
aged mantel and install the two () brackets to under-
side of mantel using four (4) 1/4-0 Philips head black
screws as shown in Figure 8. Brackets and screws can
be found in the hardware bag located inside the unit.
Unwrap the two () pre-assembled access doors and
snap into place. If the spacing between the doors and
upper lattice is not even, you can pull the doors mantel
off and adjust the upper lattice. Screw the two () jack-
ing screws that contact the front up or down as needed.
(Fig. 9)
  Follow the instruc-
tions provided with the kit.
  At least two people will
be needed to move the rebox. To ease installation, lift
the front of the stove slightly to put weight on the rear
wheels. Position the rebox so the ue collar aligns with
34
6ENTSYSTEMCOMPONENTS

ST100
 Components of the venting system.
Flexible Flue Liner
Flex Liner Adapter
(if required)
Adjustable (6” or verti-
cal) Flue Collar w/Inte-
grated Draw-Down Bar
Top of the Insert Around
Flue Opening
Washers 1/4 Dia.
1/4-0 Hex Nuts
ST493
 Measured height from the nished hearth surface to
the center bar of the ue collar.
2056O”
(521 mm)
Ref. 26”
ST2493
finished height
7/09
Possible
Handle Bracket
Locations
Mantel
Access
Door

9
Merrimack Large Insert
30004671
ST1163
merrimack mantel
Bracket and
Screws Bracket and
Screws
ST1163
 Secure bracket to mantel with two () Philips screws.
the connector. Use the leveling screws at the front of
the Insert to adjust the level. Route the power cord to
the side nearest the power supply.
   From inside the stove,
reach up and pull the ue collar into place by lining up
the two 1/4” studs in the stove top. Care should be
taken to not disturb the gasket which seals the collar
to the top. Tighten the two 1/4” nuts.
• Replace the stainless steel air tubes, if removed,
by sliding them rst to the right and then into the
mating holes on the left. Secure these in place with
the stainless steel cotter pins.
• Before installing the airwash manifold, replace the
ber bafe board and ensure it slides all the way
to the back. There should be a tight t between the
board and the iron sides of the stove.
• Replace the front air tube and secure it in place with
the cotter pin.
 


10.Install the supplied handle storage bracket by simply
sliding the at end under the right or left side of the
stove. (Fig. 7)
This completes installation of your Merrimack Large
Insert.


All Merrimack Large Insert controls are conveniently lo-
cated on the front. (Fig. 9)
Three controls regulate the performance of your Merrimack
Large Insert:
The  supplies oxygen for the re.
The variable-speed  , or rheostat, regulates
the warm air ow into the room.
An automatic setback control provides a high air setting
of restarting or reviving a re after reloading and closes
automatically once the stove reaches operating tempera-
tures.

A single air control regulates the amount of heat the re
will produce and how long it will burn.
The  is located on the upper left
side on the front of the insert. The lever regulates air for
starting, maintaining, and reviving the re.
Generally, more air entering the stove makes the re burn
hotter and faster, while less air prolongs the burn.
The Merrimack Large Insert’s air supply is increased when
the control lever is moved to the left, and decreased when
moved to the right. It may be set anywhere between the
two extremes, depending on the amount of heat desired.
(Fig. 10)
ST1157
primary air control
Air Control
Lever
ST1157




 The air control lever controls the amount of air enter-
ing the rebox.
FP2493
Merrimack controls
Air Control Lever
Fan Speed Control (Behind louvre) FP493
Merrimack Large Insert controls.
Space Between
Doors and Upper
Lattice
Jacking
Screws
Jacking
Screws

10
Merrimack Large Insert
30004671
To complement the manual setting of the air control, the
Merrimack Large Insert has an integral convection air
blower that ensures an even delivery of heat at the manual
setting you select.

The convection fan delivers a steady stream of warm air
into the room. Use the fan speed control to regulate the ow
of air into the room. A thermal switch will automatically de-
activate the fan when the stove cools down. When starting
a re in a cold stove, this switch will typically energize the
fan within about 0 minutes, after the stove heats up.
The fan speed should be set at “low” (fully closed) when
operating at low to medium burn rates and may be set
anywhere between “low” and “high” when operating at high
burn rates. (Refer to Figure 11 for fan access)
ST1156
fan speed control
Speed Control
Open Bottom Louvre to
Access Fan controls ST1156
 Fan control access.

The automatic setback air control is used when starting or
reviving a re and provides an increased ow of combustion
air to the re until the rebox is sufciently heated. This
air supply automatically resets to the desired air setting,
taking the guesswork out of operating the stove.
Figure 9 shows the automatic setback control. Move the
primary air control lever all the way to the left. Push the
primary control about one more inch to the left to open the
air shutter (the lever will spring back automatically when
released). The shutter will remain open only if the stove
is below its proper operating temperature. Once open, the
primary air control lever may be adjusted to any desired
position. Once the stove heats up to its proper operating
temperature, you will here a clicking sound conrming the
shutter has closed. This returns the stove to the output
setting of the primary air control.
This feature is primarily intended for reloading the stove
when lower air settings (low heat output) are desired, but
it is also useful any time the rebox is too cool for proper
combustion or when freshly added wood does not ignite
readily.
For maximum efciency and performance, the Merrimack
insert should always have visible ames in newly added
wood, either within the fuel pile or near the roof of the
rebox. Wood moisture, piece size, draft, weather and
rebox temperature will all have an effect on how quickly
aming occurs. The automatic setback air control is a
convenient feature allowing more user exibility and ease
of operation.

The Merrimack Large Insert is designed to burn natural
wood only; do not burn fuels other than that for which it
was designed.
You’ll enjoy the best results when burning wood that has
been adequately air-dried. Avoid burning “green” wood
that has not been properly seasoned or cordwood that is
more than two years old.
The best hardwood fuels include oak, maple, beech, ash,
and hickory that has been split, stacked, and air-dried
outside under cover for at least one to two years.
For areas that do not have a supply of hardwood, com-
monly burned softwoods include tamarack, yellow pine,
white pine, Eastern red cedar, r, and redwood. These
too should be properly dried.
Your Merrimack Large Insert will accept wood up to ”
(559 mm). Longer wood pieces work better than short
ones.
Wood should be stored under cover to maintain dryness.
Even for short-term storage, however, keep wood a safe
distance from the heater and keep it out of the areas
around the heater used for re-fueling and ash removal.


No single air control setting will t every situation. Settings
for each installation will differ depending on the quality of
the fuel, the amount of heat desired, and how long you
wish the re to burn.
The control setting also depends on your particular “draft,”
or the force that moves air from the stove up through the
chimney. Draft is affected by such things as the length,
type, and location of the chimney, weather, local geogra-
phy, nearby obstructions, and other factors.
Too much draft may cause excessive temperatures in the
Merrimack Large Insert, and could even damage internal
components. On the other hand, too little draft can cause
backpufng into the room or a very sluggish re.