On the hottest days of summer with my plasma running for hours, it barely got warm. It could certainly not warm any room as it only uses about 300 watts and much of that is used to make light. The days of 600 watt plasmas are long gone.
There is no difference in HDMI cables. If you can see the picture without visible dropouts or sparklies, the cable is working at 100%. No other cable will display a better version of that picture. You're simply wrong if you think there is a better digital cable than one that is already working.