Furnace header box having blocked condensation protection, a furnace including the header box and a blocked condensation protection system

A cold end header box of a furnace, comprising:

• a first channel having a closed end, an open end, a first channel supply port positioned to be in fluid communication with an inlet of a combustion air blower, and a first pressure port couplable to a first input of a pressure sensing device, said combustion air blower and said pressure sensing device couplable to said cold end header box;
• a second channel having a closed end, an open end, a second channel supply port positioned to be in fluid communication with said inlet of said combustion air blower, a second pressure port couplable to a second input of said pressure sensing device, and a pressure reference inlet, said second channel in fluid communication with said first channel;
• a fixed orifice located entirely outside of said first channel and said second channel;
• wherein said first channel supply port and said second channel supply port are different ports and are both located entirely within an area of said inlet of said combustion air blower;
• and
• wherein said first supply port is adjacent said closed end of said first channel and said second pressure port is adjacent said closed end of said second channel.