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

Specifications

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.

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.

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

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.