Description
The Osburn 3500 Wood Burning Fireplace Insert is one of the most powerful inserts in its class. The 3.5 cubic ft firebox is capable of handling up to a 22″ log with a maximum burn time of up to 10 hours.
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Products / Fireplaces & Stoves / Osburn 3500 Wood Burning Insert
Eligible for Tax IncentiveApprox. Heating Area: 1,000 – 2,700 sq. ft.
Max Output: 110,000 BTU/h
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The Osburn 3500 Wood Burning Fireplace Insert is one of the most powerful inserts in its class. The 3.5 cubic ft firebox is capable of handling up to a 22″ log with a maximum burn time of up to 10 hours.
| Tax Incentive | Eligible for Tax Incentive |
|---|---|
| Brand |

The Osburn 3500 Wood Burning Fireplace Insert is one of the most powerful inserts in its class. The 3.5 cubic ft firebox is capable of handling up to a 22″ log with a maximum burn time of up to 10 hours. It produces up to 110,000 BTUs with a heating area up to 2,700 square ft. A 144 CFM blower is included to help push the heat throughout the space. The Osburn 3500 insert is EPA approved with an optimum efficiency rating of up to 77% and a low 1.32 average particle emissions rate, it is rare for an insert this large to burn this clean.
The large 18 7/8″ x 11 3/4″ glass surface is the focal point of the Osburn 3500 wood insert, allowing you to enjoy the beauty of the flame while you cozy up next to the warmth of the insert. The clean lines of the insert allow the Osburn 3500 to fit with just about any decor. You can choose between the black or brushed nickel for the finish trim and door overlay to help tailor the look of the insert. You will never have to worry about a drafty fireplace again after you update your fireplace with the Osburn 3500 Wood Insert. The large heating capacity is sure to warm up your extra large space in even the coldest of winters.
| Osburn Matrix 3500 Wood Burning Insert Specifications | |
| Overall firebox volume-ft³ : | 3.5 |
| Overall firebox volume-ft³ : | 2.84 |
| Maximum burn time : | 10 h |
| Maximum heat output-dry cordwood : | 110,000 BTU/h (32.2 kW) |
| Overall heat output rate | 18,100 BTU/h (5.3 kW) to 49,500 BTU/h (14.5 kW) |
| Average overall efficiency (dry cordwood) : | 71 % (HHV) 76 % (LHV) |
| Optimum overall efficiency : | 77% |
| Optimum heat transfer efficiency : | 76% |
| Average particulate emissions rate : | 1.32 g/h |
| Average CO | 92 g/h |
| Combustion technology | Non-catalytic |
| High-efficiency certified appliance | Yes, EPA 2020 approved |
| Maximum log length | 22” |
| Log positioning | Loading over width and over depth |
| Flue outlet diameter | 6” |
| Type of chimney | Liner – ULC-S635, CAN/ULC-S640, UL1777 |
| Minimum chimney height (feet) | 15’ |
| Baffle type | C-Cast or equivalent |
| Approved for a mobile home installation | No |
| Shipping Weight | 540 lb (245 kg) |
| Door Type | Single, glass with cast iron frame |
| Glass type | Ceramic glass |
| Glass surface – dimensions (Width X Height)) | 18 7/8″ X 11 3/4″ |
| Glass air-wash system | Yes |
| Premium quality blower included (CFM) | 144 |
| Overall dimension (Height) | 24 7/8″ |
| Overall dimension (Width) | 30 3/8″ |
| Overall dimension (Depth) | 29″ |
| Door opening – dimension (Height) | 9 7/8″ |
| Door opening – dimension (Width) | 19″ |
| Firebox – dimension (Height) | 12 7/8″ |
| Firebox – dimension (Width) | 22 7/8″ |
| Firebox – dimension (Depth) | 20 1/8″ |
| Firebox lined with refractory bricks for better heat distribution | Yes |
| Stainless-steel secondary-air system improving gas combustion | Yes |
| Steel thickness – body | 3/16″ |
| Steel thickness – top | 5/16″ |
| Fireplace opening – minimum (Height) | 26 1/4″ |
| Fireplace opening – minimum (Width) | 31” |
| Fireplace opening – minimum (Depth) | 18 3/8″ |
| USA standard (emissions) | EPA |
| Canadian Standard (emissions) | CSA B415.1-10 |
| USA standard (safety) | UL 1482, UL 737 |
| Canadian standard (safety) | ULC S628 |
| Tested and listed as per applicable standards | By an accredited laboratory (CAN/USA) |
| Warranty | Limited Lifetime |
| Steel thickness – body | 3/16″ |
| Steel thickness – top | 5/16″ |
| Fireplace opening – minimum (Height) | 26 1/4″ |
| Fireplace opening – minimum (Width) | 31” |
| Fireplace opening – minimum (Depth) | 18 3/8″ |
| USA standard (emissions) | EPA |
| Canadian Standard (emissions) | CSA B415.1-10 |
| USA standard (safety) | UL 1482, UL 737 |
| Canadian standard (safety) | ULC S628 |
| Tested and listed as per applicable standards | By an accredited laboratory (CAN/USA) |
| Clearance to Combustibles* | Canada | United States | ||
| Clearance – top (measured from the platform on which the appliance is installed) | 84″ | 84” | ||
| Clearance – Combustible side mantle to unit | 9″ | 9” | ||
| Clearance – Combustible top mantle to unit | 27″ | 27” | ||
| Clearance – Combustible side wall to unit | 19″ | 19” | ||
| Clearance – from the top of the unit to the shelf | 27” | |||
| Clearance – from the top of the insert to the shelf | 27” | |||
| * 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/or web sites). | ||||
| ** Some appliances have been tested with a low ceiling. Before setting up your unit, refer to the installation manual. | ||||


The Door Overlay is required to complete the installation. The Door Overlay is available in either black or brushed nickel finish. The options for the Door Overlay allow you to tailor the look of the fireplace insert to your liking. The Black Door Overlay gives the fireplace insert more of a traditional style, while the Brushed Nickel Door Overlay gives the insert a more sleek and modern look. The Door Overlay easily installs to the insert with the included bolts.
The Faceplate is the component that flashes around the fireplace insert and covers the fireplace. The Faceplate is available in two sizes: 32″ x 44″ and 32″ x 50″. The size you choose should be based on the opening of your existing fireplace. Choose the 32″ x 44″ Faceplate size if the opening of your fireplace is less than 32″ x 44″. If your fireplace opening is greater than 32″ x 44″, you will want to select the 32″ x 50″ Faceplate size.
The Faceplate Trim is required for finishing the installation of the Regular or Large Faceplate and completes the wood insert installation. The Faceplate Trim is available in either black or brushed nickel. Choose the size for the Faceplate Trim based on the size of the Faceplate you chose. You have the option to match the Faceplate Trim to the same color as the door overlay or you can mismatch to add dimension to the style of the fireplace insert.
The 5″ Fresh Air Oval Kit is required if you plan on connecting a fresh air intake pipe. The oval adapter kit comes with the oval adapter, 2 clamps and the fresh air intake register hood. The oval adapter is intended for a 5″ fresh air intake pipe. You will have to manually ovalize the flexible intake pipe to make the connection to the adapter. The oval adapter can be positioned on either side of the insert.
The Rigid Fire Screen allows you to burn wood in the fireplace insert with the door open just like an old-time fireplace. Hear the crackle of the wood, watch the flames dance around in the firebox and relax around the wood insert on a cold winter’s night. The Rigid Fire Screen is easy to install and easy to remove when you are ready to load more wood. The fireplace insert should not be burning with the door open without the firescreen.
Rock-Flex 316Ti stainless steel chimney liner kits are UL listed and the perfect choice to install for your new wood burning insert. Each kit includes the 316Ti Flexible Chimney Liner, Vertical Appliance Connector, 13 x 13 in. Premium Top Plate, and Round Rain Cap.
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