I probably could have described the scenario a little better.
Asrock FM2A75M-DGS A75 Socket FM2 http://www.asrock.com/mb/AMD/FM2A75M-DGS/
AMD A10 5800K Black Edition 3.8GHz Socket FM2 4MB L2
2 x Crucial 4GB DDR3 1866Mhz Ballistix Elite Memory Module CL9 1.5V
1 x Corsair 430W CX Builder 80 Plus Bronze PSU
and the case is the rubbish but cheap Casecom MA-1199 Piano Black MATX Tower Case
The cupboard has a door on it with a 30mm gap to the top and at the back it is fully open so nothing stopping airflow there. I wilol probably have the door open most of the time but when the pc is off I will shut it. I didn't really think about this build as it was my first and needed something quick. (had it about 10-12 months now) and I didn't have this desk then either.
I have 2 x 22" monitors as I use it mainly for trading and it seems to heat the cpu up so am after a case and a cooler.
I suppose ideally at some point I will upgrade the motherboard so a decent case now that I could use for the future would be good.