Originally posted by: Eli
While I'm all for home made stuff, that's silly..
I mean, it will help.. but it isn't going to do much.
Most furnace filters aren't comparable to even the crappiest air filters. You could get one of the more expensive ones. Look for something that's at least has an efficiency and micron rating..
You will need to attach it to the fan better than that, though, to make it effective. Use duct tape all around it, to make sure it's sealed and all the air goes through it.
It will probably make the fan motor run hotter, but it shouldn't burn it up or be a fire hazard unless the air restriction is fairly significant.