We have an Osburn 1600 insert that came with the house when we bought it three years ago. The insert works great and really cuts our oil consumption, but I've always been annoyed by the non-thermostat fan. At night, we fill the insert with wood, but used to turn the fan to low speed in order to not have it blowing a lot cold air in the morning. This was a compromise that still had problems, not putting out as much heat as high speed when everything was hot, and still blowing cold air and wasting power by morning. This is my solution: It's a custom designed and built controller that senses the temperature at the top of the insert and sets the fan speed accordingly. The brains is a PID temperature controller from ebay that came with a sensor. I drilled and tapped a small block of aluminum to thread the sensor into and installed it on top of the insert just in front of the flue exit. It is wedged in place with two small pieces of high temp silicone gasket that seems to be withstanding the heat so far. It was pretty fiddly getting in place in such a narrow space! I put some heatsink grease on the block for better conductivity. The toggle switch has three positions, center is automatic mode, down is manual low speed, and up is manual high speed. When we start a fire, we start the sequence with the black push button. The fan stays off until about 85*C (trial and error to find useful heat on low speed) and at 125*C (more trial and error), it switches to high speed. As the fire dies down, the fan goes back to low speed at 125*C and then shuts off as temps drop below 85*C. At this point, the power is also removed from the controller, shutting everything off. This was important to me as I didn't want to have to remember to turn the controller off every morning. So far it has worked very well. My wife thinks I should remove one of the old fireplace grills and mount the box in the opening for aesthetics, but I didn't want to make it a permanent installation. I also had to remove the cord from the fan unit and install a four wire cable to the control box. I used a program called TINA to design and test the circuit before actually building it. Below is a screenshot of the schematic: It took a lot of head scratching to figure out a circuit that worked with a minimum of parts with the simplest possible user controls. The T-stat, warm, and hot contacts are all combined in the PID controller. The manual and hi/lo switches are also combined in one toggle switch. Being able to see an actual stove temp is kind of interesting; the hottest we have seen so far is just over 300*C. Hearing the fan drop down to low speed is also a good reminder to throw some more wood in.