Steady Soapstone-Lined Wood Heat for Your Masonry Fireplace

The Green Mountain Insert 70 (GMi70, Model 8450) is a non-catalytic wood fireplace insert with a flush cast iron design, soapstone-lined firebox, and factory-installed blower, in two finishes.

Key Features

• Flush cast iron design — the insert installs flush with the fireplace facing for a clean, built-in look, with an arched cast iron front in Black Matte or Brown Enamel.
• Soapstone-lined firebox — a 2.4 cu. ft. firebox lined with natural soapstone accepts logs up to 20 inches and radiates steady warmth as the fire burns down.
• Non-catalytic combustion — a single-lever primary air control adjusts the burn rate; there is no catalyst to monitor or replace.
• EPA 2020 certified using cordwood — certified at 2.3 g/hr particulate emissions with a 72% (HHV) weighted average efficiency, per the current owner's manual.
• Maximum cordwood heat output of 44,500 BTU/hr — with heating coverage of up to 2,000 square feet, depending on home layout, insulation, and operating conditions.
• Included convection blower — the unit ships complete with a factory-installed blower with automatic heat-sensor operation and a manual mode.
• HeatLife up to 8+ hours — per the current owner's manual, soapstone extends usable heat well after the active flames decline.

Product Features

Flush Cast Iron Design

The GMi70 is designed to sit flush with the fireplace facing, framing the fire with an arched European cast iron front. An optional steel surround system trims the transition to the masonry opening, and the surround coverage measures approximately 45-3/8 inches wide by 31-5/8 inches tall per current HearthStone materials.

Soapstone-Lined Firebox

The firebox is lined with natural soapstone panels over a steel firebox body. Soapstone absorbs heat during the burn and releases it gradually, moderating temperature swings and extending comfortable warmth. The overall firebox volume is 2.4 cu. ft., with an EPA loading volume of 1.95 cu. ft. and a maximum log length of up to 20 inches.

Non-Catalytic Combustion

A single primary air control lever under the ash lip regulates the burn rate from high to low. Secondary combustion air burns gases released by the wood, and an air-wash system helps keep the ceramic glass clear for viewing the fire. The glass is a clear ceramic material capable of operating at temperatures up to 2300°F.

Included Convection Blower

A blower is factory installed beneath the insert, behind the front casting. In the automatic position, a heat sensor starts the blower when the insert is hot and stops it as the insert cools; a manual position runs the blower at any time. The current dealer sheet confirms the unit ships complete with the blower.

Flexible Surround and Fireplace Fit

An optional steel surround attaches behind the cast iron faceplate, an optional lower surround panel completes a four-sided surround for raised-hearth installations, and an optional surround extension allows the insert to project 2 or 4 inches into the room, reducing the required fireplace depth. These options let the GMi70 fit a range of masonry fireplace geometries; see the accessory table below.

Full-Length 6-Inch Liner Requirement

The GMi70 must be installed with a continuous 6-inch listed stainless steel chimney liner extending from the insert to the top of the chimney, using liners listed to UL 1777, ULC S635, or CAN/ULC S640. The manual describes three connection methods, including the recommended optional Liner Hook-Up Starter Collar, and recommends a sheet metal block-off plate to reduce cold-air backdrafts.

Available Finishes and Configurations

The GMi70 is a single base model available in two finishes. Pricing varies by finish.

Specifications

Fireplace Opening, Clearances and Hearth Requirements

The GMi70 and its stainless steel chimney liner are approved for installation only within a lined masonry chimney and masonry fireplace conforming to building codes for solid fuel. Do not remove bricks or mortar from the existing fireplace, do not connect to a chimney flue serving another appliance, and note that a positive flue connection to the clay tile is not approved. The GMi70 is not intended for installation in a bedroom.

Where a fresh air intake is needed, HearthStone suggests adding a minimum of 4 inches to the width of the minimum masonry opening. The optional surround extension permits the shallower 17-5/8" or 15-5/8" installation depths by projecting the insert 2 or 4 inches into the room when installed according to the current manual.

Hearth and floor protection requirements depend on the height of the masonry hearth. If the hearth is at least 5 inches above the combustible floor, noncombustible floor protection with no specified R-value must extend at least 16 inches (USA) or 18 inches (Canada) in front of the insert. If the hearth elevation is less than 5 inches, the floor protector must have an R-value of at least 1.00 and extend at least 23 inches in front of the unit. In the USA, front and side protection is measured from the door opening; in Canada, the 8-inch side protection is measured from the side of the insert.

The standard installation leaves no projection of the convection air jacket in front of the fireplace opening; using the surround extension, the insert may project 2 or 4 inches into the room, and any additional floor protection is determined using the manual's calculation based on the existing hearth extension and the projection used. Note that some luxury vinyl plank and tile flooring may begin to warp around 110°F, so additional shielding may be necessary depending on the flooring manufacturer's limits. The current owner's manual governs every installation; review it with your installer and local building official for complete requirements.

Included Equipment

• Green Mountain Insert 70 Model 8450 wood fireplace insert
• Factory-installed convection blower (the unit ships complete with the blower)
• Two boxes of soapstone firebox lining
• Owner's manual
• Leveling bolts (quantity 2)
• Soapstone spacers (quantity 2)
• Metal fireplace-installation label
• Chimney-liner brackets (quantity 3)

Compatible Accessories

All accessories are sold separately and installed per their instructions and the current manual.

Warranty

The GMi70 is covered by HearthStone's limited warranty as published in the current owner's manual, where Limited Lifetime is defined as ten years. In summary, the applicable schedule covers external stone, cast iron components not listed elsewhere, and the clean-burning air-supply system for the Limited Lifetime period; door handles, latches, steel components, and the firebox for five years; appliance electrical components, refractory stone, vermiculite panels, and baffles for two years; and enamel finish, glass, accessories, and components not otherwise listed for one year. Warranty labor is covered in the first year through an authorized dealer when the appliance is dealer installed. Coverage extends to the original purchaser and is not transferable; conditions and exclusions apply. See the current written warranty for complete terms.

About HearthStone

HearthStone Quality Home Heating Products of Morrisville, Vermont has built stoves prized for long-lasting, comfortable heat for more than four decades. The Green Mountain Insert 70 brings HearthStone's signature soapstone lining to a flush-fitting wood fireplace insert offered through authorized dealers.

Cozy Glow Stoves is an authorized HearthStone dealer. Visit our Logan, Ohio showroom to see HearthStone products in person, or contact us with questions about the GMi70, current pricing, and installation planning.