50 feet is generally considered the maximum reliable length for HDMI cables.

What if you want to connect your set top box to a TV in another room?

• HDMI over Cat 6 coax - 150 feet. $200-$250
  Usually requires 2 coax cables
• Wireless HDMI - $190
  See Best Wireless HDMI Video Transmitter | The Wirecutter
• Remote Control Extender (IR Repeater)
  Recoton Infrared Range Extension System DSC-IR100A - Best Buy $42
  

Links:
How To Extend Your HDMI Cables - DIY Tech - Popular Mechanics