All right, so I finally completed my box today. All I have to do is sanding it down and cutting the holes for the lens and the fan.

I was just wondering something about the fan's hole. Wouldn't it make more sense for me (electronic ballast mounted externally) to put the hole at the top of the box ? (hot air rises).

It just seems to make more sense to me that way. Is there any particular reason most people do it at the bottom (besides the fact that it is usually behind the ballast) ?

Top is fine.

Thanks, that's what I thought

I put mine at the top for that reason and also to force the air to move through the light chamber from that 1/2" gap under the heat shield.

Same here... mine is at the top and on the side. it draws air up and across the bulb.

I put mine at the bottom because it was easier to install there, and because I mounted most of the heavier items at the bottom. If I eventually install a light shield, it is easier to mount it from the floor.

Given the CFMs pulled the fan and that you're only talking an offset of a few inches, there is effectively no difference between the two positions. Sure, heat rises, but not while the fan is on. Then the heat is blown out the back.

Oh, and my ballast is mounted externally, on the back of the box.

At the bottom.

It seems like someone reported that they had placed their fan at the top as well as the fresh air intake (the cooling slot), it seems the projector got hotter and hotter as the fan's exhaust was recirculated into the projector creating a vicious cycle.

I plan to place my fresh air intake on the bottom of the enclosure and the fan will be at the top rear exhausting upward at a 45º angle in an effort to avoid the above problem (if it even exists).

Thanks a lot for all the responses.

I still "feel" that I'd like my fan at the top better. I will probably cut it out tomorrow (working on the norpro right now). I tink that with the proper louvres, that potential cycle will not be an issue (the hot air exiting should be pushed towards the bottom). If I realize that it is indeed recycling hotter air, I can always use a PVC pipe and "force" the air flow in a better direction.

Somehow, it is also how I "picture" it placed (talk about a scientific explanation)

It seem that with the fan at the top that the airflow would make a much better path. Instead of trying to suck air out of the bulb area it would actually circulate it out. Then perhapse a small duct to direct it away from the intake vent would keep it from recycling. I think that is how im going to try to build mine.

My exahust and air intake were on the top and the box did get hotter. However, the exhaust and air intake where located above a drop tile ceiling. The intake had nothing to suck in except hot air. I ended up running some duct work from the intake hole to a vent that allowed the fan to suck air in from the room rather than from on top of the tiles.

I also ended up putting another 120mm fan in the duct work to help force more air into the box. The tempereature dropped from 103 in the box to a nice 85.