My heater will nearly cause you to melt however it only blows heat out of 3.5 vents.
The driver side vent by the door blows HOT and so does the center left vent, then the center right its warm and the passenger vent by the door is like the vent. what could cause this? I have checked the ducting and all seems well? Stumped!

 

dumb answer but is your vent controls in the blow or open position? 4th gen accords (which i'm assuming you have) have individual controls for each vent. check that or if it's broken.

 

(Yes ^ LOL dumb question) but yes there all open and it the passenger side vents just blow cold I am stumped