Ahh please excuse my bad attitude after nearly dying from carbon monoxide poisioning from a bad hot water tank flue. The chimney cap cracked causing the flue liner to fall in and gave 2 of us poisioning. luckily my buddy mark who was here is a volunteer fireman and recognized the symptoms.......
as is we were both very ill for a couple days.
direct vent appliances marked 99% efficent are different than regular furnaces and must have sensors to protect you from co2 and oxygen depletion.
THE RUKES ABOUT CRACKED HEAT EXCHANGERS ARE THERE BECAUSE IT HAS CAUSED DEATH AND SEVERE ILLNESS.......