HearthStone Green Mountain Insert 70 User manual

Green Mountain Insert 70 (Model 8450)
Manual: 6400-41414
R: 08/05/19
Green Mountain Insert 70
(Model 8450)
Wood Fireplace Insert
OWNER'S MANUAL
Installation And
Operating Instructions
SAVE THIS OWNER’S MANUAL FOR FUTURE REFERENCE
PLEASE READ THIS ENTIRE OWNER’S MANUAL BEFORE YOU INSTALL AND USE YOUR
NEW GREEN MOUNTAIN INSERT 70 WOOD FIRPLACE INSERT.
If this room heater is not properly installed, a house fire may result.
To reduce the risk of fire, follow the installation instructions.
Failure to follow these instructions can result in property damage, bodily injury, or even death.
Conforms to UL Std. 1482 & 737
Certified to ULC Std. S628
CONTACT LOCAL AUTHORITIES WITH
JURISDICTION (BUILDING
DEPARTMENT or FIRE OFFICIALS),
ABOUT PERMITS REQUIRED,
RESTRICTIONS AND INSTALLATION
INSPECTION IN YOUR AREA.
Safety tested according to ULC S628,
UL 737 and UL 1482 Standards
by an accredited laboratory

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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NOTES ON INSERT OPERATION AND EFFICIENCY
Rating:
You have purchased a HearthStone Green Mountain Insert 70 tested to CFR 40 part 60, subpart AAA, section 60.534(a)(1(ii)
and draft ASTM WK47329-14 where applicable. This insert is certified to comply with the U.S. Environmental Protection
Agency 2020 particulate emissions standard using cord wood. It is certified at 1.54 gr/hr. emission rate and under specific
test conditions has been shown to deliver heat at rates ranging from 14,800 to 28,600 Btu (output).
This wood heater has a manufacturer-set minimum allowable low burn rate that must not be altered. It is against federal
regulations to alter this setting or otherwise operate this wood heater in a manner inconsistent with operating instructions in
this manual.
Please refer to the Warranty section of this manual for registration instructions. In case of warranty claims, please contact
the point of original sale or the nearest authorized HearthStone dealer. Our dealer network processes all warranty claims.
Authorized HearthStone dealers can be located at www.hearthstonestoves.com.
This heater is designed to burn natural wood only. Higher efficiencies and lower emissions generally result when burning
air-dried seasoned hardwoods, as compared to softwoods or to green or freshly cut hardwoods. DO NOT BURN: Garbage,
lawn clippings, material containing rubber (including tires), materials containing plastic, waste petroleum products paints or
paint thinners, asphalt products, materials containing asbestos, construction or demolition debris, railroad ties, pressure
treated wood, manure or animal remains, salt water driftwood or other previously salt water saturated materials, unseasoned
wood, paper products, cardboard, plywood or particleboard. This prohibition against burning these materials does not
prohibit the use of fire starters made from paper, cardboard, sawdust, wax and similar substances for the purpose of starting
a fire in an affected wood heater. Burning these materials may result in a release toxic fumes or render the heater ineffective
and cause smoke.
Following the maintenance guidelines set forth in this manual will help insure the efficient use of your wood heater and
minimize visible emissions. Having your insert inspected by a trained professional on a regular basis will greatly increase
the potential for recognizing potential impacts to efficiency.
Proper draft is important to the efficient operation of your heater. Refer to the Normal Operation section of this manual for
information regarding adequate draft. Both excessive and sub-minimum draft can affect the efficiency of your wood heater.
Excessive draft can lead to over-consumption of fuel, lower overall heating capacity of the fireplace insert and potential over
firing. Low draft can result in inefficient burns, low heat output, expulsion of smoke into the living area when fireplace insert
doors are opened and an increased potential for build-up of flammable materials in the flue.
Efficiency:
Efficiency was measured and weighted using CFR 40 part 60, subpart AAA, section 60.534(a)(1(ii) and draft ASTM
WK47329-14 and CSA B415.1-10 methodology. A weighted average was used to calculate the overall efficiency across all
of the 4 burn rate categories using the higher heating value (HHV). The weighted average efficiency is 69% (HHV).
To maximize the efficiency of your wood fireplace insert make sure it is sized properly for the space you plan to heat. An
oversized fireplace insert will often be forced to burn at a lower and dirtier burn rate. Consult with your dealer for sizing and
correctly placing the fireplace insert in your home. An incorrectly placed fireplace insert can greatly reduce efficiency.
Maximizing the efficiency of your fireplace insert will heat your house quickly, burn cleaner and use less wood.
Refer to the Choosing Firewood section of this manual for appropriate fuel selection. Seasoned firewood is typically at or
near 20% moisture content. This can be measured with any number of hand-held moisture meters available through your
local hearth shop. Follow instructions included in the meter you purchase to measure fuel wood moisture content. Burn only
dry, seasoned wood as using wet wood will greatly reduce your efficiency.
CO Emissions:
The Green Mountain Insert 70 has an average CO emission rate over all burn categories of 89.4 g/hr. Wet wood or
unapproved fuel described above can greatly affect the emissions of a wood burning fireplace insert.
Smoke/Fire/CO Detectors:
It is highly recommended that smoke and CO detectors be installed throughout the heated space when a wood burning
heater is installed. Be certain to install these devices not only in the area where the wood appliance is located, but also in
bedrooms, hallways leading to other areas of the house and all common areas of the heated space. Check the batteries in
these devices and assure operation by performing whatever test operations are recommended by the manufacturer.

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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Table of Contents
INTRODUCTION.....................................................................................................................4
CODES AND SAFETY INFORMATION ..........................................................................................................................4
PERIODIC CHECKLIST AND EMERGENCY PROCEDURES.............................................................................................6
SPECIFICATIONS ..................................................................................................................7
INSTALLATION ......................................................................................................................8
UNPACKING............................................................................................................................................................8
ZONE HEATING.......................................................................................................................................................8
MASONRY FIREPLACE REQUIREMENTS....................................................................................................................8
CERTIFICATION LABEL ............................................................................................................................................9
MASONRY FIREPLACE THROAT DAMPER ..................................................................................................................9
INSTALLATION OF A COMBUSTIBLE MANTEL SHELF.................................................................................................10
HEARTH REQUIREMENTS &FLOOR PROTECTION....................................................................................................10
MINIMUM MASONRY OPENING...............................................................................................................................13
COMBUSTIBLE SURFACE REQUIRED CLEARANCES .................................................................................................13
INSTALLING THE INSERT........................................................................................................................................14
OUTSIDE AIR SUPPLY...........................................................................................................................................16
THE VENTING SYSTEM.......................................................................................................18
GENERAL INFORMATION........................................................................................................................................18
CHIMNEY AND LINER INFORMATION........................................................................................................................18
LINER CONNECTION..............................................................................................................................................19
MINIMUM CHIMNEY CLEARANCES..........................................................................................................................20
CHIMNEY LOCATION .............................................................................................................................................21
SUPPLY OF COMBUSTION AIR................................................................................................................................22
OPERATION.........................................................................................................................23
CONTROLS AND FEATURES...................................................................................................................................23
BLOWER OPERATION............................................................................................................................................23
CHOOSING FIREWOOD..........................................................................................................................................24
BUILDING AFIRE..................................................................................................................................................25
BREAKING IN YOUR WOOD FIREPLACE INSERT.......................................................................................................25
NORMAL OPERATION............................................................................................................................................26
OVER-FIRE CAUTION............................................................................................................................................27
FIRE SCREEN.......................................................................................................................................................28
MAINTENANCE....................................................................................................................29
CREOSOTE FORMATION &REMOVAL AND GENERAL MAINTENANCE..........................................................................29
GLASS AND BLOWER REPLACEMENT PROCEDURES................................................................................................30
DOOR ADJUSTMENT .............................................................................................................................................32
REFRACTORY,SECONDARY AIR TUBES AND BAFFLE ................................................................................................32
REMOVAL INSTRUCTIONS......................................................................................................................................33
ILLUSTRATED PARTS LIST................................................................................................34
REPLACEMENT KITS &OPTIONAL ACCESSORIES....................................................................................................37
TROUBLESHOOTING..........................................................................................................38
SAFETY LABEL ...................................................................................................................40
LIMITED WARRANTY ..........................................................................................................41

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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INTRODUCTION
Thank you for purchasing a Green Mountain Insert
70 wood fireplace insert from HearthStone Quality
Home Heating Products. This fireplace insert will
provide years of comfortable heat. This fireplace
insert combines the warmth and comfort of
soapstone and cast iron with the efficiency of
advanced combustion technology. The Green
Mountain Insert 70’s large glass window allows you
to enjoy the fire from a variety of locations in the
room. We trust that you will appreciate the quality of
this product.
Your Green Mountain Insert 70 wood fireplace insert
burns very efficiently and produces a large amount
of heat. However, you should not consider your
Green Mountain Insert 70 the sole heat source for
your home.
Please read this manual in its entirety. Its purpose is
to familiarize you with your fireplace insert's safe
installation, proper break-in, operation and
maintenance. It contains extremely important
information so keep it handy and refer to it often.
A qualified heating technician may need this owner’s
manual as a reference when installing this fireplace
insert in your home. There are national, state, and
local building codes that direct the technician on how
to install your fireplace insert. These codes stipulate
the dimension of stovepipe and clearances to walls,
ceilings, hearth, and other combustible surfaces.
The codes exist to reduce the risk of fire. Failure to
follow these instructions can result in fire, property
damage, bodily injury, and even death.
It is extremely important to install this fireplace insert
with the proper clearance from combustible
surfaces. You can purchase specific connector pipe
and special wall coverings as specified by this
manual and the NFPA 211 code to protect
combustible surfaces. As a general rule, keep
furniture, drapes, curtains, wood, paper, and other
combustibles at least 36 inches (92 cm) away from
the fireplace insert. Never install the fireplace insert
in or near a storage location for gasoline, kerosene,
charcoal lighter fluid or any other flammable liquids.
Install the fireplace insert in your central living area
to allow heat to radiate naturally to distant rooms. Do
not install your fireplace insert in a poorly insulated
area. This is inefficient and would likely result in
higher fuel usage.
SAFETY NOTICE:
AN IMPROPERLY INSTALLED FIREPLACE INSERT
CAN RESULT IN A HOUSE FIRE. FOR YOUR
SAFETY, CAREFULLY FOLLOW THE
INSTALLATION DIRECTIONS. CONTACT LOCAL
BUILDING OR FIRE OFFICIALS ABOUT
RESTRICTIONS AND INSTALLATION INSPECTION
IN YOUR AREA.
The safety of your fireplace insert will depend on
many factors, some of which include: distance to
combustible objects, correct venting, and adequate
chimney maintenance. Should you have any
questions, do not hesitate to contact your dealer for
additional information.
Contact your dealer for any necessary warranty
service.
This Green Mountain Insert 70 Model 8450 fireplace
insert is warranted by:
HearthStone Quality Home Heating Products, Inc®
317 Stafford Ave.
Morrisville, Vermont 05661, USA
www.hearthstonestoves.com
CODES
When you install your Green Mountain Insert 70
wood fireplace insert, it is imperative that you adhere
to all Federal and local codes. Obtain these codes
from either of the following sources:
American National Standards Institute, Inc. (ANSI)
1430 Broadway
New York, NY 10018
www.ansi.org
National Fire Protection Association, Inc. (NFPA)
Battery March Park
Quincy, MA 02269
www.nfpa.org
SAFETY INFORMATION
Read and understand this Owner's Manual
thoroughly before installing and using this
fireplace insert.
Make sure to install your fireplace insert:
According to the manufacturer's
recommendations
In accordance with all applicable codes
With the proper sized chimney

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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When installed and operated as described in
these instructions, the Green Mountain Insert 70
wood insert is suitable for use in residential
installations. The Green Mountain Insert 70
wood insert is not intended for installation in a
bedroom.
The information given on the certification label
affixed to the appliance always overrides the
information published, in any other media
(owner’s manual, catalogues, flyers, magazines
and web sites).
Mixing of appliance components from different
sources or modifying components may result in
hazardous conditions. Where any such changes
are planned, HearthStone should be contacted
in advance.
Any modification of the appliance that has not
been approved in writing by the testing authority
violates CSA B365 (Canada), and ANSI NFPA
211 (USA).
Connect this insert only to a listed stainless steel
chimney liner for use with solid fuel.
If required, a supply of combustion air shall be
provided to the room.
Do not connect to or use in conjunction with any
air distribution ductwork unless specifically
approved for such installation.
Do not connect this unit to a chimney flue
serving another appliance.
The insert and its stainless steel chimney liner
are to be installed only within a lined masonry
chimney and masonry fireplace conforming to
building codes for use with solid fuel. Do not
remove bricks or mortar from the existing
fireplace when installing the insert.
In Canada, the CSA B365 Installation Code for
Solid Fuel Burning Appliances and Equipment
and the CSA C22.1 Canadian National Electrical
Code are to be followed in the absence of local
code requirements. In the USA, the ANSI NFPA
211 Standard for Chimneys, Fireplaces, Vents
and Solid Fuel-Burning Appliances and the ANSI
NFPA 70 National Electrical Code are to be
followed in the absence of local code
requirements.
This insert must be installed with a continuous
chimney liner of 6" diameter extending from the
insert to the top of the chimney. The chimney
liner must conform to the Class 3 requirements
of CAN/ULC-S635, Standard for Lining Systems
for Existing Masonry or Factory-built Chimneys
and Vents, or CAN/ULC-S640, Standard for
Lining Systems for New Masonry Chimneys.
The insert is not approved for use with a so-
called “positive flue connection” to the clay tile of
a masonry chimney.
When using your fireplace insert, follow these
safety precautions:
Never burn kiln dried, painted or treated wood in
this fireplace insert.
DO NOT BURN GARBAGE. Never burn
garbage or trash, colored or glossy paper,
solvents, plywood, artificial logs, cardboard, or
driftwood, in this fireplace insert.
Never burn coal in this fireplace insert.
DO NOT BURN FLAMMABLE FLUIDS.
DO NOT USE CHEMICALS OR FLUIDS TO
START THE FIRE. Never use gasoline,
kerosene, charcoal lighter fluid, or other
flammable fluids to start or invigorate the fire.
These fuels will cause dangerous burning
conditions in the fireplace insert. Keep all such
materials away from the fireplace insert.
Never use a wood grate or other device to
elevate the fire.
Never allow logs in the firebox to hit the glass
when the door is closed.
Never slam the door or use the door to force
wood in to the fireplace insert.
Never over-fire your fireplace insert. (See page
27)
Never put articles of clothing or candles on a hot
fireplace insert.
Never connect the fireplace insert to a flue used
by another appliance.
Other safety guidelines:
Keep all combustible items such as furniture,
drapes, clothing, and other items, at least 36"
(0.92 m) from the fireplace insert (See page
114)
Install a smoke detector, preferably in an area
away from your wood fireplace insert.
Keep a fire extinguisher handy. We recommend
the type rated "A B C."

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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Dispose of ashes properly. (See page 29)
Keep children and pets away from the fireplace
insert when it is burning; they could be seriously
injured by touching a hot fireplace insert.
Clean your chimney system as needed. (See
page 29)
Outside combustion air may be required if:
1. This solid-fuel-fired appliance does not
draw steadily, smoke rollout occurs, fuel
burns poorly, or back-drafts occur whether
or not there is combustion present.
2. Existing fuel-fired equipment in the house,
such as fireplaces or other heating
appliances, smell, do not operate properly,
suffer smoke roll-out when opened, or
back-draft whether or not there is
combustion present.
3. Opening a window slightly on a calm
(windless) day alleviates any of the above
symptoms.
4. The house is equipped with a well-sealed
vapor barrier and tight fitting windows
and/or has any powered devices that
exhaust house air.
5. There is excessive condensation on
windows in the winter.
6. A ventilation system is installed in the
house.
If these or other indications suggest that infiltration
air is inadequate, additional combustion air should
be provided from the outdoors. Outside combustion
air can be provided to the appliance by using the
optional outside air kit #94-53500
PERIODIC CHECKLIST
Perform each of these tasks at the specified
intervals.
At the End of Every Week:
Empty ashes from the firebox, sooner if the
firebox is full.
At the Beginning of Every Other Month:
Depending upon your use of the fireplace insert,
visually inspect the chimney connector and
chimney for creosote. (see page 29)
Check door seals using the "dollar bill test." -
When the fireplace insert is cool, shut the door
on a dollar bill. If the bill pulls out without any
resistance, then your fireplace insert’s door is
not sealing properly. To tighten the seal, adjust
the door latch mechanism or change the door
gasket. (Refer to page 29.)
At the End of Every Season:
Dismantle the chimney connector and clean it
thoroughly. Replace any pieces that show signs
of rust or deterioration.
Inspect and, if necessary, clean your chimney.
Clean out the inside of the fireplace insert
thoroughly.
Inspect all door gasket material and replace if
worn, frayed, cracked or extremely hard.
EMERGENCY PROCEDURES
If you have a stovepipe or chimney fire, follow these
instructions:
1. If the fire is too threatening, leave the area and
call the fire department immediately! If not,
perform the next three steps.
2. Close the primary air control.
3. Close the stovepipe damper (if present).
4. Keep the fireplace insert front door closed!
WARNING: DO NOT ATTEMPT TO PUT OUT A
STOVEPIPE OR CHIMNEY FIRE BY THROWING
WATER ONTO THE FIREPLACE INSERT,
STOVEPIPE, OR CHIMNEY. THE EXTREMELY
HIGH TEMPERATURE OF SUCH FIRES CAN
CAUSE INSTANTANEOUS STEAM AND SERIOUS
BODILY HARM.
Once the chimney fire expires, leave the primary air
control closed and let the fire in the fireplace insert
die out completely. Inspect the fireplace insert,
stovepipe, and chimney thoroughly for any sign of
damage before firing the fireplace insert again. You
must correct any damage before using your fireplace
insert again. We recommend having the fireplace
and the insert verified by a certified sweep or a fire
marshal before using the insert after a chimney fire.
Establish a routine for the fuel, wood burner and
firing technique. Check daily for creosote build-up
until experience shows how often you need to clean
to be safe. Be aware that the hotter the fire the less
creosote is deposited, and weekly cleaning may be
necessary in mild weather even though monthly
cleaning may be enough in the coldest months.
Contact your local municipal or provincial fire
authority for information on how to handle a chimney
fire. Have a clearly understood plan to handle a
chimney fire.

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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Specifications
Maximum Heat Output:
28,600 BTUs per hour of cordwood (based on
independent laboratory test results).
Floor Size of Heated Area:
Up to a maximum of 2,000 square feet. Factors
unique to your home can reduce the square
footage the fireplace insert will heat. Home
insulation value, number and efficiency of
windows, floor plan, fireplace placement, quality
of the fuel and other conditions may limit the
heating ability of the fireplace insert.
Firebox Capacity:
2.4 cubic feet.
Maximum Log Length:Up To 20” (50.8 cm).
Emissions: 1.54 g/hr.
Burn Time: HeatLife Up to 8+ hrs. Note: The
amount and weight of wood contained per cubic
foot of firebox volume can vary from 10 to 25
lbs. per cubic foot depending on type of wood,
moisture content, packing density and other
factors.
Fireplace insert Dimensions:
Height: 25 3/4”(65.4cm)
Width: 33 1/2" (85.1cm)
Depth: 19 5/8" (49.8cm)
Weight: 513 lbs. (233 kg)
Connector Size: 6" (152 mm) diameter
Metal Chimney: 6" (152 mm) inside diameter
Masonry Chimney: 6” (152 mm) inside diameter
(round flue), 8” x 8” (203 x 203 mm) (square
flue)
Crate Dimensions: H-34” W-30” L-35” or
86.5x76.5x 89cm
Optional Equipment:
Outside Air Kit 94-53500
Steel Surround 94-5950110
Surround Lower Panel 94-5950510
Surround Extension 94-5950010
Fire Screen Insert 94-69500
Figure 1 –Green Mountain Insert 70 Dimensions

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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Installation
Read this chapter to obtain a sound understanding
of how to properly install your Fireplace Insert.
Contact the following agency for more information:
National Fire Protection Agency
Batterymarch Park
Quincy, MA 02269
1-800-344-3555
1-617-770-3000
www.nfpa.org
UNPACKING
HearthStone packages your Green Mountain Insert
70 wood fireplace insert with the greatest care so
that it ships safely. Under certain circumstances,
however, damage may occur during transit and
handling. When you receive the Green Mountain
Insert 70, carefully unpack and inspect the fireplace
insert and all accompanying parts. Ensure that all
parts are included inside the fireplace insert. If any
parts are damaged or missing, please contact your
authorized HearthStone dealer immediately.
Be sure to remove the packaging material in the
flue collar and above the baffle before installing the
chimney.
PACK LIST
1. Green Mountain Insert 70 Model 8450
Wood Fireplace Insert
2. Two boxes containing soapstone lining
3. Owner’s Manual
4. Leveling bolts (x2)
5. Spacers for soapstone (x2)
6. Metal label for fireplace installation
7. Brackets for chimney liner (x3)
ZONE HEATING
Your new Green Mountain Insert 70 wood insert is
a space heater, which means it is intended to heat
the area it is installed in, as well as spaces that
connect to that area, although to a lower
temperature. This is called zone heating and it is an
increasingly popular way to heat homes or spaces
within homes.
Zone heating can be used to supplement another
heating system by heating a particular space within
a home, such as a basement family room or an
addition that lacks another heat source.
Houses of moderate size and relatively new
construction can be heated with a properly sized
and located wood insert. Whole house zone heating
works best when the insert is located in the part of
the house where the family spends most of its time.
This is normally the main living area where the
kitchen, dining and living rooms are located. By
locating the insert in this area, you will get the
maximum benefit of the heat it produces and will
achieve the highest possible heating efficiency and
comfort.
The space where you spend most of your time will
be warmest, while bedrooms and basement (if there
is one) will stay cooler. In this way, you will burn
less wood than with other forms of heating.
Although the insert may be able to heat the main
living areas of your house to an adequate
temperature, we strongly recommend that you also
have a conventional oil, gas or electric heating
system to provide backup heating.
Your success with zone heating will depend on
several factors, including the correct sizing and
location of the insert, the size, layout and age of
your home and your climate zone. Three-season
vacation homes can usually be heated with smaller
inserts than houses that are heated all winter.
MASONRY FIREPLACE REQUIREMENTS
The masonry fireplace must meet the minimum
requirements found in the building code enforced
locally, or the equivalent for a safe installation.
Contact your local Building Inspector for
requirements in your area. An inspection of the
fireplace should include the following:
CONDITION OF THE FIREPLACE AND CHIMNEY:
The masonry fireplace and chimney should be
inspected prior to installation, to determine that
they are free from cracks, loose mortar,
creosote deposits, blockage, or other signs of
deterioration. If evidence of deterioration is
noted, the fireplace or chimney should be
upgraded and/or cleaned prior to installation.
Masonry or steel, including the damper plate,
may be removed from the smoke shelf and
adjacent damper frame if necessary to

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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accommodate the insert’s chimney liner,
provided that their removal will not weaken the
structure of the fireplace and chimney, and will
not reduce protection for combustible materials
to less than that required by the building code.
CHIMNEY CAPS:
Mesh type chimney caps must have
provision for regular cleaning, or the mesh
should be removed to eliminate the
potential of plugging.
CLEARANCE TO COMBUSTIBLES:
The fireplace should be inspected to make
sure that there is adequate clearance to
combustibles, both exposed combustibles
to the top, side, and front as well as
concealed combustibles, in the chimney
and mantle area. Your local inspector
should have information on whether older
fireplaces are of adequate construction.
OPENING SIZE:
Refer to page 13 Minimum Masonry
Opening for suitable size fireplace
openings.
CERTIFICATION LABEL
The label is on a metal plaque in the blower space
below the firebox. It is attached with a lanyard to the
firebox so it can pull out far enough for inspection.
Take care when lifting and installing the insert to
keep the label inside the firebox to avoid any
damage.
Figure 2 - Label Location
Since the information given on the certification label
attached to the appliance always overrides the
information published in any other media, it is
important to refer to it to have a safe and compliant
installation. The model and the serial number can
also be found on the label.
It is recommended to note the insert serial number
on this manual. It will be needed to identify the
version of the appliance in the event replacement
parts or technical assistance is required. It is also
recommended to register the warranty online at
www.hearthstonestoves.com
MASONRY FIREPLACE THROAT DAMPER
If the fireplace's draft control system is to remain in
the masonry fireplace, it must be locked open for
access of the chimney liner or removed entirely. If
you remove draft control system from the masonry
hearth, you will need to install the metal plate
(27009), supplied with the owner’s manual kit,
indicating that the masonry hearth has been
modified. It must be secured inside the masonry
hearth, in a visible place and easy to locate.

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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INSTALLATION OF A COMBUSTIBLE
MANTEL SHELF
It is possible to install a combustible shelf with a
maximum depth of 12" at a height of at least 27"
above the insert. At a height of more than 27", the
shelf must still have a maximum depth of 12".
Figure 3 –Mantel Shelf
HEARTH REQUIREMENTS &FLOOR
PROTECTION
Ensure you protect combustible flooring with a
covering of noncombustible material. The minimum
floor protection must be met under the fireplace
insert and extend beyond the fireplace insert as
follows:
FLOOR PROTECTION
Canada
USA
B
18" (457 mm)1
16" (406 mm)1
M
8" (203 mm)
N/A
N
N/A
8" (203 mm)
Figure 4 –Hearth Requirements
1From door opening. The depth of the hearth extension in
front of the insert is included in the calculation of the floor
protector’s dimensions. The masonry hearth should be at
least 5" (127 mm) higher than the combustible floor in
front of it and a floor protection must extend at least 16"
(406 mm USA) and at least 18" (457 mm Canada) without
an R value. If the hearth elevation is lower than 5" (127
mm), the non-combustible floor protector in front of the
insert should have an R value equal or greater than 1.00
and shall extend 23" (584 mm) in front of the unit.
MAXIMUM MANTEL
SHELF DIMENSION (X)
MANTEL SHELF
CLEARANCES (I)
12"(305 mm) max.
27"(686 mm) min.

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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To determine the need to add floor protection (D)
beyond the hearth extension, do the following
calculation using the data in following table: D = B -
(A - C).
The standard configuration of the insert leaves no
projection of the convection air jacket in front of the
fireplace opening. Therefore, the minimum
projection is 0''. Although it is possible to position
the insert to obtain a projection of 2'' (51 mm) or 4''
(102 mm) of the convection air jacket in front of the
fireplace opening with the use of the surround
extension. The choice of the configuration will
depend on the previous installation instructions and
compliance with building code.
If the value (D) is negative or zero, additional floor
protection in front of the unit is not needed because
the masonry fireplace hearth extension is large
enough. If the value (D) is positive, an additional
floor protection in front of the hearth extension at
least equivalent to the result (D) must be added.
Maximum
Extended
Minimum
Extended
A
Dimensions of
the hearth
extension
Dimensions of the
hearth extension
B
See the following
sections
See the following
sections
C
2" / 4"
(51 / 102 mm)
0"
(0 mm)
D
D=B-(A-C)
D=B-(A-C)
E
10" / 12"
(254 / 305 mm)
14"
(356 mm)
Air
Jacket
Back from
fireplace facing
2" or 4"
Flush with
fireplace facing
Figure 5 –Floor Protection
INSTALLATION RAISED 5” OR LESS
If non-combustible material floor protection needs to
be added in front of and level with the hearth
extension of the masonry fireplace (F = 5" or less),
an R-value equal to or greater than 1.00 is required
and should extend at least 23" (584 mm) in front of
the unit (B).
Figure 6 –Installation 5” or Less
INSTALLATION RAISED MORE THAN 5”
If the extension of the masonry hearth is raised
more than 5" (127 mm) from the floor protection, a
non-combustible material, without an R-value, must
extend at least 16" (406 mm in USA) or 18" (457
mm in Canada) in front of the unit.

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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Figure 7 –Installation More Than 5”
R-VALUE
There are two ways to calculate the R-value of the
floor protection. First, by adding the R-values of
materials used, or by the conversion if the K factor
and thickness of the floor protection are given.
To calculate the total R value from R values of the
materials used, simply add the R-values of
materials. If the result is equal to or greater than the
R-value requirements, the combination is
acceptable. R-values of some selected materials
are shown below:
Table: Thermal Characteristics of Common Floor
Protection Materials*
MATERIAL
CONDUCTIVITY
(k) PER INCH
RESISTANCE (R)
PER INCH
THICKNESS
Micore®160
0.39
2.54
Micore®300
0.49
2.06
Durock®
1.92
0.52
Hardibacker®
1.95
0.51
Hardibacker®500
2.3
0.44
Wonderboard®
3.23
0.31
Cement mortar
5.00
0.2
Common brick
5.00
0.2
Face brick
9.00
0.11
Marble
14.3 –20.00
0.07 –0.05
Ceramic tile
12.5
0.008
Concrete
1.050
0.950
Mineral wool
0.320
3.120
insulation
Limestone
6.5
0.153
Ceramic board
(Fibremax)
0.450
2.2
Horizontal still air**
(1/8")
0.135
0,920**
* Information as reported by manufacturers and
other resources
**Horizontal still air can’t be ‘stacked’ to accumulate
R-values; each layer must be separated with
another non-combustible material.
Example 1:
Required floor protection R of 1.00. Proposed
materials: four inches of brick and one inch of
Durock® board.
Four inches of brick (R = 4 x 0,2 = 0,8) plus 1 inch
of Durock® (R = 1 x 0.52 = 0.52).
0.8 + 0.52 = 1.32. This R value is larger than the
required 1.00 and is therefore acceptable.
Example 2:
In the case of a known K and thickness of
alternative materials to be used in combination,
convert all K values to R by dividing the thickness of
each material by its K value. Add R values of the
proposed materials as shown in the previous
example.
Example:
Common brick K value = 5
Thickness = 4"
R value = Thickness/K = 4/5 = 0.8
Durock K value =1.92
Thickness = 1"
R value = Thickness/K = 1/1.92 = 0.52
Total R value = .8 + 0.52 = 1.32

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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MINIMUM MASONRY OPENING
Refer to the Figure ‘Clearance to Combustibles’
MINIMUM MASONRY OPENING
J
23 5/16 " (592 mm)
K
28 7/8 " (733 mm)*
L
19 5/8 " (498 mm)**
* Where a fresh air intake is needed, we suggest
you add a minimum of 4’’ to the width of the
minimum masonry opening.
** If surround extension is used L = 17 5/8" or 15
5/8". If installed without the surround extension L =
19 5/8".
COMBUSTIBLE SURFACE REQUIRED
CLEARANCES
Note: Dimensions shown in the following figures are
from the body of the fireplace insert unless otherwise
indicated.
It is very important to follow minimum clearances for
chimney connectors to combustibles such as walls
and ceilings when installing the fireplace insert near
combustible surfaces.
The clearances shown in this section have been
determined by test according to procedures set out
in safety standards ULC S628 (Canada), UL1482
(U.S.A.) and UL737 (U.S.A.). When the insert is
installed so that its surfaces are at or beyond the
minimum clearances specified, combustible
surfaces will not overheat under normal and even
abnormal operating conditions.
NO PART OF THE INSERT MAY BE LOCATED
CLOSER TO COMBUSTIBLES THAN THE
MINIMUM CLEARANCE FIGURES GIVEN.
CLEARANCES
F
16" (406 mm)
G
9" (229 mm)
H
27" (686 mm)
I
27" (686 mm)
Q
84" (213 cm)
MAXIMUM THICKNESS
O
5" (127 mm)
P
12" (305 mm)
Figure 8 –Clearance to Combustibles

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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INSTALLING THE INSERT
1. Remove the contents of the firebox. This will
include the owner’s manual packet, 2 boxes of
soapstone for lining the firebox, spacers for the
floor stone, leveling bolts and enamel touch-up
if applicable.
2. Remove the front casting from the insert.
a. Remove the two screws visible below
the ash lip.
b. Tilt the frame up slightly, then LIFT the
frame up and off the hanger tabs on top
of fireplace insert.
c. Carefully remove the front casting from
the fireplace insert. It may be easiest
to open the door slightly and allow the
door handle to swing out of the way.
3. With two or more people, lift the insert and
remove it from the pallet.
4. Insert the leveling bolts. There are 2 nuts
welded to the outside of the firebox, one in each
of the lower rear corners. Thread the included
leveling bolts into the nuts.
5. If installing the optional steel surround, attach
the surround brackets according to the
instructions included with the steel surround
before placing the insert in the fireplace
opening.
6. Place the insert in the fireplace opening and
connect the liner to the inlet on top of the insert.
Follow the instructions in the Liner Installation /
Liner Connection section of this manual.
7. Level the insert. Adjust the bolts installed in
Step 4 to level the insert if needed.
8. (Optional) Install the Steel Surround following
the instructions included with that optional
accessory. Connect the surround to the
previously installed brackets.

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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9. (Optional) Install the Lower Surround Panel
following the instruction included with that
optional accessory.
10. (Optional) Install the Surround Extension
following the instructions included with that
optional accessory. To install the surround
extension, the surround must be installed in
position 4” back from the front face of the insert.
The extension can also be as a 2” extension by
cutting the extension panels and installing the
surround 2” back from the front of the insert.
11. Install the blower switch plate on the front
casting:
a. Gently remove the blower switch
assembly from the lower left corner of
the insert. It is very important not to
disconnect the wires.
b. Attach the blower switch plate to the
lower rear left corner of the front
casting using the two screws in the
bosses.
12. Install the front casting following the procedure
from Step 2 in reverse order.
a. Carefully position the front casting on
the fireplace insert. Make sure the air
control handle passes through the
opening in the front casting below the
ash lip. It may be easiest to open the
door slightly to avoid hitting the door
handle.
b. Be careful not to pinch the blower
switch wires.

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
16
c. LIFT the front casting up and onto the
tabs on top of fireplace insert. Guide
the hanger brackets onto the tabs and
let the front casting rest on the top edge
of the firebox.
d. Position the front casting by sliding it
left or right. Center the front casting
casting with the door. Carefully check
that the door can open fully without
making contact with the front casting.
e. Install the two screws below the ash lip.
These screws should pass through the
square holes in the hanger brackets
(attached to be front casting) and back
into the holes they were removed from
in Step 2. You may need to lift the front
casting slightly to engage the screws.
13. Install the soapstone in the firebox following the
diagram below.
a. Install the floor bricks first.
b. Install the 2 spacer channels along the
sides of the firebox.
c. Install the side stones, inserting the top
of each stone behind the retaining steel
then standing the stone against the
firebox wall.
d. Install the rear stones, inserting the top
of each stone behind the retaining steel
then standing the stone against the
firebox wall.
SIZE
QUANTITY
1
9" X 4.5" X 1.25"
14
2
9" X 4.25" X 1.25"
2
3
9" X 2" X 1.25"
4
4
6.5" X 4.5" X 1.25"
2
5
Spacer Channel
2
14. Inspect the installation.
a. The door opens fully and seals shut.
b. The air control moves left and right.
c. The blower turns on an off.
OUTSIDE AIR SUPPLY
(Optional Kit #94-53500)
You can connect an outside air source directly to
this fireplace insert using an optional outside air kit.
The advantage of providing outside air directly to
the fireplace insert is that the air used by the
fireplace insert for combustion is taken from outside
the residence rather than from within the room
where the fireplace insert is located.
The International Residential Code (IRC) does not
allow the outside air duct to terminate higher than
the appliance. Some building officials restrict
vertical rise in the duct’s termination. HearthStone
recommends the termination be at the same level,
or lower than the air intake on the fireplace insert.
Locate the termination of the duct on the outside
wall of the home in such a manner to avoid the

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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possibility of obstruction by snow, leaves or other
material.
Install the Outside Air Supply:
Using pliers, remove the rectangular knock-out
plate (A) located on the left or right side of the
convection air jacket. Choose the side that is best
for your installation.
Note: Only remove the knock-out that will be
connected to the fresh air inlet.
Figure 9 –Outside Air Inlet
Figure 10 –Outside Air Kit Detail
Then, install the fresh air kit adapter (B) using 4
screws (C). Secure the flexible pipe1(E) to the
adapter (B) using one of the adjustable pipe clamps
(D). Secure the other end of the pipe to the outside
wall termination (F) using the second adjustable
pipe clamp (D). The outside wall termination (F)
must be installed outside of the building.
1The pipe must be HVAC type, insulated, and must
comply with ULC S110 and/or UL 181, Class 0 or
Class 1.

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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The Venting System
GENERAL INFORMATION
The venting system, made up of the chimney and
the liner inside the chimney, acts as the engine that
drives your wood heating system. Even the best
insert will not function safely and efficiently as
intended if it is not connected to a suitable chimney
and liner system.
The heat in the flue gases that pass from the insert
into the chimney is not waste heat. This heat is
what the chimney uses to make the draft that draws
in combustion air, keeps smoke inside the insert
and safely vents exhaust to outside. The heat in the
flue gas can be seen as the fuel the chimney uses
to create draft.
BLOCK-OFF PLATE
To reduce the possibility of a cold air back draft
from the masonry chimney into the room, the
installation of a sheet metal block-off plate (A) is
recommended. When fabricating the block-off plate,
cut the pipe hole slightly larger than the liner
diameter and pass the liner through the hole. Install
the block-off plate and secure it with masonry nails.
Seal the joints between the plate and the chimney
with high temperature silicone and use stove
cement to seal between the pipe and the plate.
In Canada, the CSA B365 Standard permits ‘Roxul’
type wool to be stuffed around the liner as it passes
through the throat area as an alternative to a sheet
metal block-off plate. However, this method is less
efficient than using a plate.
Figure 11 –Block Off Plate 1
Figure 12 –Block Off Plate 2
SUITABLE CHIMNEYS
Your wood insert will provide optimum efficiency
and performance when connected to a 6-inch
diameter chimney liner. The connection to a
chimney having a diameter of at least 5 inches
(Canada only) is permitted, if it allows the proper
venting of combustion gases and that such
application is verified and authorized by a qualified
installer. Otherwise, the diameter of the flue should
be 6 inches. The reduction of liner diameter to less
than 6” should only be done if the total height of the
masonry chimney is greater than 20 feet.
LINER INSTALLATION
The use of a chimney liner (rigid or flexible) is
recommended to ensure the best performance. To
ensure an optimal draft, it is also strongly
recommend adding a minimum of 12" rigid liner
between the top of the masonry chimney and the
rain cap. In all cases, liners should be installed in
accordance with the liner manufacturer’s
instructions, including instructions for extension
above the masonry.
Use chimney liners listed UL 1777, ULC S635 or
CAN/ ULC S640.
In order to connect the insert to the liner, refer to
the section LINER CONNECTION.

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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ATTENTION INSTALLER: When positioning the
unit in a fireplace opening prior to the flue
installation, install the insert into the opening until
the top lip of air jacket is flush with fireplace facing.
If lag bolts or anchors are to be used to secure the
insert, the hole locations should be marked with the
unit in place. Remove the insert and locate the
anchors.
Figure 13 –Liner Installation
LINER CONNECTION
Two options are possible to connect the liner to the
insert:
Liner Starter Adaptor
Two options are possible:
Install the chimney liner starter adapter, provided
with the chimney liner. Follow the chimney liner
starter adapter manufacturer's instructions.
In order to connect the chimney liner starter adapter
to the flue outlet, install three brackets with the
three screws, all provided in the user manual, on
top of the insert.
Figure 14 –Liner Connection
The long end of the brackets must be attached to
the insert. Insert the chimney liner into the flue
collar of the unit and secure the liner to the brackets
with three self-tapping screws (not included).
The dealer may offer a liner fastening system
(HearthStone accessory #94-67500), sold
separately. Follow the installation instructions
provided with the liner fastening system.
Figure 15 –Liner Fastening System

Hearthstone Quality Home Heating Products, Inc ®Green Mountain Insert 70 (Model 8450)
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Liner Offset Adaptor
A liner offset adapter, sold separately, can also be
installed. This should only be installed if no other
option is possible and if the total height of the
fireplace and chimney is at least 20 feet. This kind
of adaptor is restricting the free flow of exhaust
gases and may result in smoke roll-out from the
insert when the door is open for reloading. When
installing a liner offset adapter, secure the three
brackets provided in the user manual on top of the
insert. The long end of the brackets must be
attached to the insert. Then, follow the instructions
in the manual provided with the liner offset adapter
kit.
Figure 16 –Offset Adaptor
MINIMUM CHIMNEY CLEARANCES
The top of the chimney should be tall enough to be
above the air turbulence caused when wind blows
against the house and its roof. The chimney must
extend at least 1 m (3 ft.) above the highest point of
contact with the roof, and at least 60 cm (2 ft.)
higher than any roof line or obstacle within a
horizontal distance of 3 m (10 ft.).
Figure 17 –Min. Chimney Height 1
Figure 18 –Min. Chimney Height 2