Osburn 3500 Wood Insert (OB03510) High-Efficiency Fireplace Insert for Spacious Heating
How does the Osburn 3500 Wood Insert (OB03510) enhance heating efficiency in larger homes?
The Osburn 3500 Wood Insert (OB03510) is engineered to deliver exceptional heating performance for larger spaces. Its expansive 3.5 cubic foot firebox accommodates logs up to 22 inches, providing a maximum heat output of 110,000 BTU/h, effectively heating areas between 1,000 and 2,700 sq. ft. This insert features an air-wash system to maintain clear glass, a heavy-duty cast iron door, and a 130 CFM heat-activated blower for efficient heat distribution. It meets EPA 2020 emissions standards with an average particulate emission rate of 1.32 g/h.
NOTE: Shown with required faceplate, faceplate trim, and door overlay (not included). The faceplate, faceplate trim, and door overlay must be purchased to complete this unit.
Required Accessories
- Black or brushed nickel door overlay
- Faceplate kit Medium (32" x 44") or Large (32" x 50")
- Black or brushed nickel faceplate trims
Also, check the available Osburn 3500 Wood Insert w/ 5.5" x 25' Forever Flex Liner Kit OB03510K.
Why Choose Osburn 3500 Wood Insert
The Osburn 3500 combines robust heating capabilities with high efficiency, making it an ideal choice for homeowners seeking reliable warmth and reduced heating costs in spacious living areas
Key Features
- Fuel type: Dry cordwood (16" recommended)
- Recommended heating area-ft²: 1000- 2,700
- Overall firebox volume-ft³: 3.5
- EPA loading 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
Manuals for OB03510 of Osburn
- Installation and Owner's Manual for Osburn 3500 Wood Insert OB03510
- Specifications Sheet for Osburn 3500 Wood Insert OB03510
Specifications for Osburn 3500 Wood Insert OB03510
- Combustion technology: Non-catalytic
- High-efficiency certified appliance: Yes, EPA 2020 approved
- Maximum log length: 22"
- Log positioning: Loading over the width
- Chimney diameter: 6"
- 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: 540lb (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" (Width) 30 3/8" (Depth) 29"
- Door opening – dimension: (Height) 8 3/4" (Width) 17 1/2"
- Firebox – dimension: (Height) 12 7/8" (Width) 22 7/8" (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" (Height) 31" (Height) 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
Minimum clearances to combustibles
(Data expressed in inches. 1 inch = 25.4 mm)
Canada
- Clearance - top (measured from the platform on which the appliance is installed) - 84"
- Clearance - Combustible side mantle to unit - 9"
- Clearance - Combustible top mantle to unit - 27"
- Clearance - Combustible side wall to unit - 19"
- Clearance - from the top of the unit to the shelf - 27"
United States
- Clearance - top (measured from the platform on which the appliance is installed) - 84"
- Clearance - Combustible side mantle to unit - 9"
- Clearance - Combustible top mantle to unit - 27"
- Clearance - Combustible side wall to unit - 16"
- 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, catalogs, flyers, magazines, and/or websites).
Note: Some appliances have been tested with a low ceiling. Before setting up your unit, refer to the installation manual.
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Let customers speak for us
from 4072 reviewsI was able to get a Novus 33 in brick refractory back for my NG Novus fireplace insert. Novus is a high demand item and Flame authority was only supplier without a huge delay from manufacturer. I recommend them for all fireplace needs.

Great service and great product

Product is great, free shipping was good, and unpacking and installing it was easy. Customer support was great too, both with the sales and shipping carrier. After much research…the Modern Flames Redstone is the one.

A+ = both the sale, the shipping process, and the product

I purchased burner and fire box. I emailed and spoke with Jim . He helped me from start to finish. Great service
The mantel required a little bit of sanding and prep before painting, but was good quality. Flame Authority did an excellent job shipping and it arrived by freight in perfect condition.
The mantel assembled well. I ended up using some construction adhesive to glue the legs on to make it a little more sturdy. I cut pocket holes in the top to attach it to the wall.
Very happy with our purchase!

I shopped for a grill for two people. I want it to last for ten years or more. I want it to get really hot for grilling steaks after they have been cooled sous vide. I want it to be useful also for lower temp cooking. This Blaze grill is perfect for me and my wife. Our purchase through Flame Authority was completed with no problems. I am totally satisfied with this grill and highly recommend it for anyone with similar needs.

Came as advertised and without any delays. Arrived quickly. No issues and would buy from flame authority again.

I wanted to make sure of the size and features of this oven. I called Flame Authority and Mary answered the call. She gave me all the details and I was really amazed coz she really knows what she is selling. Expert with sales and communication. Thumbs Up!

I bought the stove couple weeks ago and ended up having a chance running it a few days I am very pleased with the outcome of the amount of heat it gets out also with the amount of hours it burns at least eight hours. I would recommend this for anyone who is looking for hours of heat output. At first when I bought it I didn’t quite know if mine hopes will be for filled but now they are happy with it. I would recommend this to anyone as a trusted tester of it I am very pleased of the outcome it rains.!

Nice , polite and helpful, when you would call with questions.Fireplace looks nice and throws a decent amount of heat , just a bit of a delay in delivery. Ended up getting it End of January, right before guests arrived. But still only took 3 weeks to get. Thank you Flame Authority !!!

I didn't expect to have this fireplace earlier than the lead time they promised. It looks stunning in my living room and now we are prepared for the upcoming winter season! I am happy with all the updates! Customer service representatives keep on updating me with the process of my order until delivery they are checking it for you! 10 stars for Flame Authority!

Simply beautifully designed. Very efficient. Looks gorgeous in our mid century modern home in a corner space. Will save us $$$ on electric heat bills and is easy to clean with fireplace glass cleaner.

I believe it was David Novak that helped me. Someone ALWAYS answered the phone and located this burner when I couldn't find it anywhere else. It almost seemed too good to be true. But it wasn't. The burner is now nestled in my new outdoor kitchen and am very pleased.

Thank you for a very smooth transaction. the remote is very useful. It is very easy to install

This unit puts out serious heat. We are in northern Idaho where winters get brutal, and this heats up our entire 1,800 sq ft log home with no trouble. I love how large the firebox is. I can load it before bed and still have coals in the morning. It is not just functional either; the big glass window makes for an amazing view of the flames. Totally satisfied. Honestly, I think we have cut our firewood use by a third compared to our old unit.
We got this installed in October and have used it daily since. It is so efficient that I often need to let it die down because the house gets too warm. I never expected to be cracking windows open in December! The firebox is huge. I can fit bigger splits without chopping everything down. The heat spreads throughout our 2,000 sq ft home with help from ceiling fans.