I was recently calculating the amount of BTUs that are loss through the windows during winter and this made me think of the amount of heat that my fireplace generates and then throws outside through the vent.
Even just the pilot light on the fireplace will generate 100,000's of BTUs per month. I figured that it might be worthwile to invest in a fireplace fan. Looking around, most of the fans are 150$+ and then I would need something special because I don't have a switch to contol the outlet in my fireplace. So a 200$ solution.
I was completely surprised to see that my fireplace had holes already perfectly lined up for a 120mm PC fan!! Here is my solution inspired by an intructable I found online:
3 x Slipstream 120mm PC fans, 0.26A each - 0$ I had them on deck already
1 x Zalman fanmate 2 fan controller - 0$ had it already
2 x fan connection y splitters - 0$ I had them on deck already
1 x AC-DC adaptor 12V 2A - 0$ had it already
24 x tie wraps to secure everything - 0$ I had them on deck already
The result is very efficient and very quiet. At maximum intensity, the fans move about 180CFM, consume 9 watts and are almost silent. At minimum, you cannot hear the fans and they still push around 30-60 CFM (hard to estimate) and only consume 4 watts. I leave the fans running at minimum when the pilot is open and maximum when the fireplace is running.
I was lucky to have all the spare parts lying around from years of building PCs for family and acquaintances. Realistically, you would spend about 30$ for the parts most of which will be high quality fans. If you don't care about noise, you could shave 10-15$ off.
I am thinking of adding a temperature switch or physical interuptor mounted to the outside of the fireplace. We will see.
