FRFP
Item #: OB03510
SKU:
Starting at:
$3,899.00
The 3500-I is the largest insert Osburn makes, and the reason to choose it over the Matrix 2700 is straightforward: a 2.88 cubic foot firebox against 1.94. That is roughly 50% more wood per load, which translates into longer burns and more output for the same amount of tending.
If you are supplementing a furnace on cold evenings, the smaller inserts are plenty. If wood is doing real work in your heating plan — carrying the house through a winter week, or through an outage — the firebox volume is what you are actually buying.
Larger fireboxes are historically dirtier; there is more fuel and more opportunity for incomplete combustion. The 3500-I holds 1.6 g/h of particulate while carrying the biggest load in the range, which is the genuinely impressive number on its spec sheet. Non-catalytic, so no combustor to replace on a schedule.
It also has one of the largest glass surfaces in its category, which does two things: you see more fire, and radiant heat comes through the glass rather than only off the surround.
At 29" deep the 3500-I needs a substantial existing fireplace to slide into. This is the most common reason a large insert order gets unwound. Measure the depth of your firebox at the floor, not at the lintel, and check that the depth holds all the way back.
A wood insert must connect to a continuous stainless liner running the full chimney height — listed to ULC-S635, CAN/ULC-S640 or UL1777 — with a minimum 15 ft chimney. Venting an insert into a bare masonry flue is neither safe nor code-compliant. Price the liner with the appliance.
Give us your firebox depth and we will tell you honestly whether the 3500-I fits or whether you want the Matrix 2700 — (540) 212-9374.
| Data expressed in inches. 1 inch = 25.4 mm (Single Wall Pipe / Double Wall Pipe) | Single Wall Pipe | Double Wall Pipe |
|---|---|---|
| Clearance - Side Wall | 19" | – |
| Clearance - Top (Measured From the Platform on Which the Appliance Is Installed) | 84" | – |
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Q: Why is the efficiency as per the EPA’s test data smaller than the publicized optimum efficiency?
A: EPA refers to the CSAB415.1-10 standard for the calculation of the appliance’s efficiency. The efficiency reported as per EPA’s directives consists of an average between four different burn rates, ranging from the lowest burn rate (air intake completely closed) to the highest burn rate (air intake completely open). The optimum efficiency that we publicize is the efficiency obtained according to the same test data, but for the low burn rate only. This efficiency is more realistic for a majority of users whose heating needs require that the unit be used to maximize burn times.
Q: Why is the BTU according to EPA test data smaller than the one advertised?
A: You will notice a difference between the BTU output as per the EPA’s test data and what is advertised on our web site and/or product literature. The maximum BTU output we advertise is what will be obtained with a full load of seasoned cordwood inserted inside the firebox. The EPA output, on the other hand, is what has been obtained during emissions testing. The EPA test procedure requires that a special type of wood is used and positioned inside the firebox in a manner that does not represent the way the firebox volume would normally be utilized using seasoned cordwood. The EPA test load is typically much smaller. Hence, the BTU as per the EPA’s test data is reduced. The BTU output that should be considered by a normal user is the one we advertise for seasoned cordwood.
Q: Will my insert work in the case of a power failure?
A: Your insert can be used in a power failure. An insert is built like a wood stove. The only thing that will not work in a power failure is the blower. Operating your insert without the blower will not damage the unit. The disadvantage is that you will not benefit from the heat circulation around the insert’s jacket. Inserts come with a blower because a large portion of the unit is inserted into a masonry opening. The heat that radiates from the portion of the firebox inserted into the masonry hearth does not reach the room as it would with a freestanding wood stove. This is why inserts have a jacket built around the back portion of their firebox. The heat is trapped inside that jacket and is pushed back in front of the stove and into the room with a blower. Without electricity, you will not recover as much heat from the unit. The radiating heat will come mainly from the glass and the front portion of the insert.
Q: Why does my wood insert blower not move a lot of air?
A: All of our inserts and blowers are designed to complement each other. It is a matter of achieving the greatest amount of heat transfer from the unit. The key is to design the insert so air can move and extract the greatest amount of heat without cooling the firebox and hindering the efficiency of the unit. If the blower velocity were to be increased, it would give the impression that the unit heats more. However, it would actually blow cooler air and reduce the unit's efficiency. A hot firebox will burn better and cleaner. A slower but hotter air displacement is therefore always preferable. The same principle applies to the heat sensor available on many models. It is better for the heat sensor to activate the blower later, when the unit is very hot, rather than activating it too early and blow cooler air when the unit is still completing its start-up phase.
Q: Can I install a liner with a 5-inch or 5.5-inch diameter?
A: All of our inserts are designed to function with a 6" liner. However, it is adequate to install a 5" or 5.5" liner when the masonry chimney is too tight for a 6" liner. Under certain conditions, the probability of a drafting issue is increased, which could favor smoke spillage and/or reduce combustion quality. But generally speaking, the vast majority of homeowners who properly install a 5" or 5.5" liner and use good heating techniques will be very satisfied with the performance of their wood insert.
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