Ok, I am soon to be getting my parts for my first PC build but have one decision to make when assembling.
I will have a Coolermaster Gladiator 600 with a Corsair HX650 PSU.
The gladiator 600 has a bottom mounted PSU with ventilation for a downward facing fan however I dont know if I should face it up or down as the case does not seem to be that high off the ground, but at the same time I dont want it sucking hot air in from the case.
If the bottom of your case has a grill for the fan to be facing downwards then I would put it in that way. It should suck cool air in from underneath your case instead of warm air from inside your case, interrupting your air flow.
concur, with a cavet - If possible mount a filter over the bottom vent holes. The cleareance is normally OK if the case is NOT setting on a high pile rug. The air near the floor is the "dustest. I cut a board (or plexiglass) to set the Case on and used a "cleanroom face mask" as a filter.
The effects of mounting with the fan ontop, depending on case airflow may not be a big factor for the PSU - my "Inside" case temp is normally only a couple of degress above ambient. However; you may disrupt the airflow inside the case and reduce the airflow across the CPU, or more likely air flow for the GPU. With top mounted PSU this is not as much of a problem.
Note: with Top mounted PSU the fan intake is normally from inside the case so orientation should not be a big thing. You can always check both ways - If no difference on GPU (max load - use fur mark) temp and on CPU (max load - use Prime 95) then place it with the fan on top (less dust and in the Long run lower temp as dust increases heat biuldup, other wise place on bottem and use a filter.
shovelnose - you are correct about a decrease in airflow, but it should be minor. Have you ever looked inside one after a year- electronics have a bad rep for dust build-up and it can seriously effect the ability to disipate heat. So I still recommend a filter, just not a dense one that inhibits air flow.
once i replaced the psu in someonew pentium one 133mhz pc. It had failed be ause the fan didnt spin anymore. Why? BEcause there was no empty space inside the psu- it was just a big wad of dust. Took tgat out, replaced a bad cap, put in new fan, and it works fine last i heard. Howevrr that pc was more than 10uears old!!!