Well right now its pretty cool in my room, because its only about 80 degrees outside. But yeah when it comes to mid day and I live in california. It gets pretty hot in the room. I have a small little fan I can put on the side of my case to give it more air. But dust particles would get in the case and I dont know if thats good for it. I know dust is going to get into it either way.
How hot is your house right now? Heatsinks work by a difference in temperatures so if your house is quite hot the CPU will be hotter than it would be if your house were cool, generally the difference between ambient temp and CPU temp is fixed for a given CPU load so if your CPU normally idles 8 C above ambient, then ambient gets increased to say 32 C your CPU is going to idle at 40C.
Do you have an OC applied right now? Also what are the rest of the specs in the system?