Built my system about 3 weeks ago and I never realized but I just noticed that i mounted the PSU with the fan facing towards the bottom of the case and is completely covered by a mount. My temperatures appear to be relatively cool (running around 30-35 C idle) and while gaming, getting about 45 C. Case temperature is around 20 C. Going through the hassle of having to literally redo everything is not really going to be fun but I'd rather do that then see my PSU fail, are there any known issues with the bottom fan not having clearance? I know that in the past when i've built computers, the fan was covered when I mounted on the top and never had any issues. Running a Antec ECO PSU btw.
personally i wouldnt leave the fan facing downwards without adequate clearance and ventelation... one of my pc,s uses a NZXT M59 case which has a 120mm width vent at the bottom and this works fine with bottom mounted psu,s with the fan facing downwards
however in hot summer months and without enough cooling the psu will get extremely hot and its a sure bet this will affect the unit in the longrun.... that said many psu including antec are designed to operate at some crazy tempertures and this may save the day
on the other side ( pardon the pun ) if you have the fan facing upwards its only going to draw in warm air from the case which could be even worse..
you could easily mod the case and drill some 5mm holes for added ventelation..... theres no set method but 9 or 16 in a square design would give some much needed cooling ....