Hearthstone Stoves Green Mountain 20 Freestanding Wood Stove

Compact TruHybrid™ Catalytic Wood Stove Sized for Small Spaces Cast iron construction with a soapstone-lined firebox and TruHybrid™ catalytic combustion, the Green Mountain 20 is sized for cabins, small homes, and rooms up to 575 square feet. Key Features TruHybrid™ combustion combining primary, secondary, and catalytic tertiary combustion with a 78.5% HHV weighted-average efficiency EPA certified at 1.14 g/hr under the 2020 particulate emissions standard Up to 23,000 BTU per hour of Maple cordwood, heating up to 575 square feet Soapstone-lined firebox that absorbs the heat of the fire and radiates gentle, long-lasting warmth Burn times up to 9.5 hours on low, with HeatLife™ up to 20 hours per the current owner's manual Burns full-size cordwood up to 18 inches long (16 inches recommended) in a slim 14.7-inch-wide body Top 6-inch flue outlet with optional rear and side heat shields to reduce clearances Product Features TruHybrid™ Catalytic Combustion The TruHybrid™ system combines primary, secondary, and tertiary combustion using a catalytic combustor to deliver clean, efficient burns that surpass 2020 EPA clean air standards. The stove is certified at a 1.14 g/hr emission rate and, under specific EPA test conditions, has been shown to deliver heat at rates ranging from 14,545 to 20,507 BTU per hour. A bypass control and a supplied catalyst temperature indicator help you engage the catalyst at the correct operating temperature for the cleanest burn. Soapstone and Cast Iron Construction The Green Mountain 20 combines a cast iron body with a soapstone-lined firebox. Soapstone absorbs the high heat of the fire and then radiates a gentle heat into the room, extending comfortable warmth well after the flames die down. A large ceramic glass window provides a full view of the fire. The 2026 HearthStone catalog identifies the Green Mountain family of EPA certified room heaters as made in Vermont. Sized for Small Spaces Designed as a traditional log burner for tight footprints, the Green Mountain 20 heats up to a maximum of 575 square feet. Factors unique to your home, including insulation, windows, floor plan, stove placement, and fuel quality, may reduce the area the stove will heat. The 1.0 cubic foot firebox accepts cordwood up to 18 inches long, with 16-inch logs recommended. Heat Shield and Outside Air Options Optional rear and side heat shields can be installed individually or together to reduce required clearances to combustible walls. The optional Outside Air Starter kit connects the stove's air intake to a minimum 3-inch outside air duct (ducting supplied by others), with a 3-inch to 4-inch increaser available when a 4-inch duct is needed. An outside air kit is required in all mobile-home installations. Available Finish and Configuration Finish Part ID MSRP Notes Black Matte 8620-0010 $2,699 Sole current configuration; cast iron with soapstone-lined firebox; front load; wood fuel Specifications Specification Value Combustion technology TruHybrid™ catalytic (primary, secondary, and catalytic tertiary combustion) Maximum heat output Up to 23,000 BTU per hour of Maple cordwood EPA test-condition heat output 14,545 to 20,507 BTU per hour (output, specific test conditions) HHV efficiency 78.5% (weighted average, higher heating value) EPA certified emissions 1.14 g/hr (2020 particulate standard, crib wood) Heating area Up to a maximum of 575 sq. ft.; home-specific factors may reduce coverage Firebox capacity 1.0 cu. ft. Maximum log length Up to 18" (16" recommended) Burn time Up to 9.5 hours on low, per the current owner's manual HeatLife™ Up to 20 hours, per the current owner's manual Height 28" Width 14.7" Depth 24.9" Weight 250 lb, per the current owner's manual Flue outlet Top, 6" diameter Chimney connector size 6" diameter Metal chimney 6" inside diameter, listed Type HT (UL 103 or ULC S629) Masonry chimney 6" round flue or 8" x 8" square flue, code-approved with liner Required chimney draft Between -0.06" and -0.10" water column; install a stovepipe damper for drafts above -0.10" water column Recommended chimney height 16 ft minimum to 30 ft maximum from the top of the stove Certification Conforms to UL 1482-2022; certified to CAN/ULC S627:2023; PFS Report F25-444 Fuel Natural seasoned cordwood only Crate dimensions 40" H x 29" W x 36" L Clearances and Hearth Requirements The Green Mountain 20 is a freestanding room heater only. It must not be installed into a factory-built fireplace or any fireplace. Clearance dimensions are measured from the furthest point on the cast body of the stove unless otherwise indicated. In the table below, A is the stove body side to the side wall, B is the connector to the side wall, C is the stove body rear to the rear wall, D is the connector to the rear wall, E is the stove body corner to a diagonal wall, and F is the connector corner to a diagonal wall. Optional side and rear heat shields reduce the listed clearances. Parallel installation A Side (stove) B Side (connector) C Rear (stove) D Rear (connector) E Corner (stove) F Corner (connector) Single-wall pipe, no heat shields 13¾" 21" 10" US / 15¼" CAN 15¾" US / 21" CAN 9½" US / 12½" CAN 18" US / 21" CAN Single-wall pipe, side heat shields 11¾" US / 13¾" CAN 19" US / 21" CAN 10" US / 15¼" CAN 15¾" US / 21" CAN 9½" US / 12½" CAN 18" US / 21" CAN Single-wall pipe, rear heat shield 13¾" 21" 10" US / 15¼" CAN 15¾" US / 21" CAN 9½" US / 12½" CAN 18" US / 21" CAN Single-wall pipe, all heat shields 11¾" US / 13¾" CAN 19" US / 21" CAN 10" US / 15¼" CAN 15¾" US / 21" CAN 9½" US / 12½" CAN 18" US / 21" CAN Double-wall pipe, no heat shields 13¾" 20¾" 9" 14½" 9½" 18" Double-wall pipe, side heat shields 9" 16" 9" 14½" 9½" 18" Double-wall pipe, rear heat shield 13¾" 20¾" 3½" 9" 9½" 18" Double-wall pipe, all heat shields 9" 16" 3½" 9" 4" 14" In Canada, per CSA B365, installations with single-wall pipe require a minimum clearance of 18" from the flue to a combustible surface, regardless of a smaller clearance noted on the product label. Double-wall connector clearances shown are specific to Simpson DuraVent DVL; check your pipe manufacturer's specifications. The current owner's manual also publishes complete through-wall and alcove clearance tables. The minimum unshielded alcove width with double-wall pipe and side heat shields is 32¾", and the minimum alcove ceiling height is 78½" from the floor with either a single-wall or double-wall connector. Alcove and through-wall installations must follow the exact configuration tables in the manual. Chimney connector clearance A B Single-wall pipe, through-the-wall flue exit, with rear heat shield 17¾" US / 21" CAN 14¾" US / 18" CAN Single-wall pipe, through-the-wall flue exit, no rear heat shield 16¾" US / 21" CAN 13¾" US / 18" CAN Double-wall pipe, with rear heat shield 11" 8" Double-wall pipe, no rear heat shield 16¾" 13¾" Single-wall connector clearance to the ceiling is 18". For double-wall connector clearance to the ceiling, refer to the connector pipe manufacturer's specifications. Hearth and floor protection: The Green Mountain 20 does not require an insulated hearth pad and has no R-value requirement. Combustible flooring must be protected with a covering of noncombustible material. The minimum floor ember protection is 27½" wide x 37½" deep for US installations, including a 16" front extension measured from the firebox front and 8" side extensions measured from the firebox sides. For installations in Canada, the minimum is 30⅝" wide x 47½" deep, including an 18" front ember-protection extension and 8" side extensions. Rooms with luxury vinyl plank or luxury vinyl tile flooring require extra consideration, as some of these floors begin to warp at 110° Fahrenheit; consult the flooring manufacturer and add shielding if necessary. Mobile-home installations: The stove may be installed in a mobile home in accordance with 24 CFR Part 3280, subject to special requirements in the owner's manual. These include an outside air kit in all mobile-home installations, permanent attachment of the stove to the floor, a Mobile Home Chimney and Connector Kit conforming to UL 103 or CAN/ULC S629 with a stainless spark-arrester cap, no installation in a sleeping room, keeping the front door closed except during startup and loading, burning wood fuel only, maintaining the structural integrity and vapor barrier of the home, required chimney termination geometry, and removal of the chimney when the mobile home is transported. Included Equipment Green Mountain 20 Model 8620 woodstove Owner's manual Hardware kit: four feet with carriage leveling bolts, mounting bolts, flat washers, and lock washers; air control handle and nut; catalyst temperature indicator Three refractory floor stones, shipped in the firebox and assembled before final installation Compatible Accessories Accessory Part ID MSRP Compatibility or requirement note Rear Heatshield 96-68200 $49 Clips onto the back of the stove to reduce rear clearances Side Heatshield, Left or Right (single) 96-68205 $69 Clips onto either side of the stove; one shield per side; install on both sides to reduce both side clearances Outside Air Starter 96-53400 $109 Connects the air intake to a minimum 3" outside air duct (ducting supplied by others); required for all mobile-home installations; in Canada, requires floor attachment and a damper allowing 100% closure 3" to 4" Outside Air Increaser 90-53308 $49 Adapter used with the Outside Air Starter when a 4" outside air duct is needed Warranty The Green Mountain 20 is covered by HearthStone's limited warranty to the original purchaser, including limited lifetime coverage (defined as 10 years) on stone, cast iron not listed elsewhere, and the wood clean-burning air-supply system; 5-year coverage on door handles and latches and on steel components and the firebox; 2-year coverage on refractory and vermiculite panels and baffles; and 1-year coverage on the enamel finish, accessories, glass, and other listed components. The catalytic combustor is warranted separately by its manufacturer, Applied Ceramics, with a two-year replacement warranty followed by a prorated schedule. Conditions, exclusions, and registration requirements apply; refer to the owner's manual for complete warranty terms. About HearthStone Hearthstone Quality Home Heating Products, Inc. of Morrisville, Vermont handcrafts soapstone and cast iron stoves that combine natural materials with advanced clean-burning combustion technology. The 2026 HearthStone catalog identifies the Green Mountain family of EPA certified room heaters as made in Vermont. Visit our showroom to see HearthStone quality in person and to discuss the right installation for your home.