Buck Stove Model 91 Catalytic Stove Size Guide

Under specific EPA test conditions, the Model 91 delivers heat at rates ranging from approximately 10,400 to 62,745 BTU per hour. The weighted average efficiency across all burn rate categories is 79.5% HHV per the owner's manual. Emissions rate is 1.2 g/hr, well below the EPA 2020 limit for cordwood appliances. The Model 91 is rated to heat 1,800 to 3,200 square feet — the largest heating envelope in the Buck Stove wood-burning lineup we carry.

• Large homes and great rooms (1,800 to 3,200 sq ft) that need primary heat from a single appliance.
• Open-plan main living areas where the included blower can move heated air to adjacent rooms through doorways and open architecture.
• Owners who want the longest burn times for unattended overnight heating and minimal reloading frequency. Catalytic combustion excels at extended low-rate burns.
• Existing masonry fireplaces (minimum 31-3/4 W × 23-1/2 H × 15-1/2 D inches) converted to a sealed wood stove insert for dramatically improved efficiency over an open fireplace.
• Households comfortable with periodic catalyst maintenance — visual inspection three times per heating season, catalyst replacement every 10,000+ hours of operation.
• Homes in cold climates (Zone 5 and above) where high BTU output capability matters for cold-snap performance.

• Mobile or manufactured homes. The Model 91 manual states it is not designed for installation in a mobile home. For mobile home installation, choose the Buck Stove Model 21.
• Zero clearance or pre-fabricated fireplaces. The Model 91 insert installation is for all-masonry fireplaces only.
• Small homes under 1,500 square feet. The Model 91 is oversized for compact heating. For 800 to 1,800 sq ft, choose the Model 21.
• Cooking and baking. The Model 91 is a dedicated heater without a cooktop or oven. For wood cooking, choose the Homesteader.
• Off-grid installations without electrical service. The Model 91 requires a 115V AC outlet for the blower. The stove will operate without the blower running but heat distribution and efficiency drop significantly.
• Connection to chimney flue serving another appliance. The Model 91 manual prohibits shared flue installation.
• Connection to air distribution duct or system. Prohibited by the manual.
• Use with fire grates. Build the wood fire directly on the firebricks; do not use a grate or elevate the fire.

• Cold climate (Zone 5-7): The Model 91 covers its full rated range. Use the upper end of the BTU envelope during cold snaps; medium-to-low burn rates for shoulder seasons.
• Moderate climate (Zone 4): The Model 91 is well-matched for primary heating in homes 1,800 to 3,200 sq ft. Most operation will be at medium burn rates with damper closed and catalyst working.
• Mild climate (Zone 3 and below): The Model 91 may oversize for typical demand in homes under 2,500 sq ft. Consider whether the Model 21 (rated to 1,800 sq ft) is a better match.
• Cathedral ceilings or two-story open plans: Heat stratification reduces effective heated floor area. The included blower significantly improves distribution; ceiling fans on low (reverse direction in winter) also help.
• Drafty or poorly insulated homes: Insulation upgrades return more comfort per dollar than upsizing a heater. Have the installation contractor evaluate the home before sizing.

The table below reflects typical sizing recommendations under average insulation and 8 foot ceiling assumptions. Actual results depend on home insulation, climate zone, layout connectivity, air sealing, and how the catalyst is maintained over time. An NFI-certified installer can evaluate your specific home.

• Hearth extension: Minimum 24 inches in front of firebox opening, minimum 8 inches to either side of firebox opening.
• Wood trim above: Wood trim above the fireplace must be at least 20 inches above the top of the unit and maximum 1/2 inch thick.
• Mantel or brackets: Mantel or mantel supports must be at least 30 inches above the top of the stove.
• Minimum fireplace dimensions: Height 23-1/2 inches; Width 31-3/4 inches; Depth 15-1/2 inches.
• Fireplace kit required: PA FP91 standard fireplace kit (oversized fireplace kit available separately for larger openings).
• Not for zero clearance or pre-fabricated fireplaces.

• Material: Non-combustible, minimum 3/8 inch thickness.
• Width: 50 inches wide.
• Extends: 16 inches from door opening in front of the stove, 8 inches from door opening on each side, and under the chimney connector for rear vent runs.
• Clearance reductions: For clearance reductions using wall protectors, refer to NFPA-211 Code. Tested and listed wall protectors with 1 inch dead air space and floor-to-ceiling installation can reduce clearances; unlisted/untested wall protectors require 1-1/2 inch air space.

• Chimney type: 8 inch UL 103 HT factory-built chimney complying with Standard for Factory-Built Chimneys for Residential Type and Building Heating Appliance, or code-approved masonry chimney with a flue liner.
• Minimum chimney height: 15 feet total height.
• Chimney location: Buck Stove recommends an interior chimney location (not on an outside wall) for best draft performance.
• Connector: 24 ga minimum blued or black steel chimney pipe for single wall installation. Do not use galvanized pipe.
• Connector joints: Secure each section with at least three sheet metal screws or rivets.
• Single appliance flue: Do not connect this unit to a chimney flue serving another appliance.
• Masonry chimney sizing: If oversized, flue liner is recommended to maintain proper draft on a catalytic stove.

• Outlet: 115V AC at the install location.
• Power cord: Do not run cord under the unit or in high traffic areas.
• Blower controls: Rheostat (variable speed) on side of unit; Automatic/Off/Manual switch behind right cover door.
• Automatic mode: Blower controlled by internal thermostat reacting to temperature of air between stove walls.
• Manual mode: Blower operates continuously at the rheostat-selected speed.

The catalyst must reach 700 to 900 degrees Fahrenheit before catalytic combustion begins. During start-up from a cold stove, maintain a medium-to-high firing rate for about 15 to 20 minutes before pushing in the bypass damper (closing it). Start the fire with dry kindling, paper, and small split wood with the bypass damper fully open (pulled out). Once gas temperatures reach 600 degrees Fahrenheit (typically within 2 to 3 minutes), the catalyst can begin working. Once the combustor is working, heat generated in it by burning smoke keeps it working.

• Catalyst probe location: To the right of the bypass damper rod.
• Normal operating temperature: Above 1,000 degrees Fahrenheit.
• Inspection schedule: Visually inspect the catalyst at least three times during the heating season for physical degradation.
• Signs of catalyst end-of-life: Loss of heating efficiency; increased smoke from the chimney; inability to maintain operating temperatures above 500 degrees Fahrenheit during steady-state operation.
• Catalyst lifespan: Typically 10,000 to 12,000 hours of operation.
• Catalyst replacement: Order from Applied Ceramics directly (770-448-6888); part is a set of three 2 inch by 3-1/2 inch by 6 inch by 25 cell ceramic substrate units. New Buck Corporation does not handle catalyst replacements.
• Federal regulations: It is against federal regulations to operate this wood heater with the catalytic element deactivated or removed.

• Do not hot-fire the stove. Excessive temperatures damage the catalyst substrate.
• Avoid flame impingement. Strong, fast drafts or hot fires with all air controls open can torch the catalyst, breaking down the ceramic.
• Do not run with door open beyond what is needed for refueling.
• Burn dry, naturally seasoned hardwood only. Wood should be dried at least 12 months before burning. Wet wood produces water vapor that drops catalyst temperature and can cause plugging, clogging, and thermal shock.
• Clean the catalyst once per year. Use plain water, a soft brush, or low-pressure air only. Soak in warm or hot (not boiling) water for 20 minutes, allow to cool at room temperature, rinse under medium pressure, dry thoroughly before reinstalling.
• Do not burn: treated wood, coal, garbage, cardboard, solvents, colored paper, trash. Burning these can poison the catalyst or coat it with fly ash that renders it ineffective (not covered under warranty).

The Model 91 is designed to burn dry, naturally seasoned hardwood. Higher efficiencies and lower emissions result from air-dried seasoned hardwoods compared to softwoods or freshly cut hardwoods. Green or freshly cut hardwoods (high moisture content) will not produce the BTU output needed to heat your home and will result in low catalyst temperatures and low BTU output.

• Best wood species: Oak, maple, ash, beech, hickory, locust.
• Seasoning time: 6 to 12 months stacked under cover with air circulation. Wood seasoned outside uncovered may have 40% moisture content; properly seasoned wood in a covered environment will have less than 20% moisture content.
• Stack pattern: Criss-cross under a shelter to allow air flow and protect from rain.
• Maximum log length: 22 inches front-to-back or 22 inches side-to-side. The 4.4 cu ft firebox accommodates large loads for extended burn times.
• Load placement: Place wood from front to back; do not use a grate or elevate the fire.
• Recommended firewood: The National Audubon Society notes Beech is considered the best wood for a fire — a cord of well-seasoned Beech produces as much heat as 169 gallons of fuel oil; Sugar Maple and Red Oak follow at 166 gallons; White Ash 154; American Elm 130; White Birch 124; White Pine 94.

• Refueling: Open the bypass damper before opening the door. Open the door slowly to prevent smoke spillage. Place small split wood and kindling on a coal bed; place larger logs on top.
• Ash removal: Remove ashes when ashes get to 2 to 3 inches deep. Leave approximately 1 inch of ash on the firebox bottom to maintain a hot charcoal bed. The ash pan is located at the left side under the hearth behind the cover door — open the cover door and slide the ash pan out.
• Turn off the blower before removing ashes. Be sure to turn the blower back on when finished.
• Ash disposal: Place in a metal container with a tight-fitting lid on a non-combustible floor or on the ground away from combustible materials until cinders have thoroughly cooled.

Compare the Model 91 against the Homesteader and Model 21, or browse the full Buck Stove collection.