The house I just bought has a basement that is uninsulated. There is a fireplace down there that I would like to try to use to provide some heat the the upstairs of the house. There is a stairwell near the wood burner and I can get the basement up to 80 degrees, but I can't get the heat to circulate upstairs. Eventually, I'm going to put some cold-air return registers in the far corner of the upstairs to help to circulate the air, but I don't want to do that until I get the exterior basement walls insulated so I'm not losing alot of my heat through the cinder blocks.

So in the near-term, I built this sheet-metal shroud to retain the heat that is coming off of the firebox. I then boxed the end off with a round 6" aluminum duct and then ran the duct in the rafters to a register that I cut in the floor upstairs. You can see the shroud and ducting here:

Some heat trickled up through the ducting, but not enough to make a difference in the temperature upstairs. Additionally, the shroud was getting very hot which means there was a lot more heat that could be harvested. So I bought a 300cfm inline fan and put it on the "downstream" side of the shroud blowing towards the register. The inlet side was drawing the hot air from under the shroud and pushing it through the ducting to the upstairs. I drew a picture so you can see what I'm talking about. (the fan is depicted in green):

This worked GREAT as I was able to feel heat blowing like crazy out of the register and I was able to get the upstairs up to 77 degrees if I really burned hot in the fireplace. I ran into a problem however in that the air on the downstream side of the shroud must have gotten too hot for the fan, and it tripped the thermal protector switch and killed the motor.

So I purchased another inline fan (this one 400cfm) and figured I would put it on the upstream side of the shroud and have the fan pull cold air from the basement, and push it through the shroud and up the ducting. You can see a picture of this here:

I bought the bigger fan because I thought that the extra "oomph" it provided would be enough to push enough volume of air through the open space of the shroud and still have decent velocity coming out of the register. That didn't seem to work though because the shroud isn't completely sealed and it was barely moving any air out of the register so that isn't going to work for me.

So, I need to somehow have the fan not be exposed to the heat on the downstream side of the shroud, but still be effective at moving the hot air from under the shroud into the ducting. I am thinking about putting a "T" on the downstream side of the shroud and connecting the fan to push straight up the ducting and having the 90-degree opening attached to the shroud to hopefully have the airflow create a vacuum that would suck the hot air into the ducting with the air that will be moving from the fan running. What do you guys think of that approach? Here is an example of what I'm talking about:

If the air being blown by the fan wanted to back-feed into the shroud instead of going up the ducting, I was thinking about fabricating a small piece of metal that would block the opening back into the shroud but would still allow air from the shroud to enter the duct, kind of like this (yellow would be the diverter):

So that's where I'm at, and I'm open to any/all suggestions for how I can get this to work like it did when I had the fan directly on the downstream side of the fan, but I can't have the fan exposed to that much heat. Thanks a lot everyone!