Fat burning is a percentage game, yes increasing intensity burns more but at a less of a percentage than increasing time served, therefore if you are soley looking to get rid of fat the longer easy paced workouts will ultimatly see better results than killing yourself for 20-30 mins.
As boredom is a factor you probably dont want to know that max fat burn occurs when glycogen stores are depleted.....on average this normally occurs after 60-90mins of steady workout.
Try taking you resting heart rate in the morning as you wake, 72 seems quite high for 27 year old.
If 72 is correct then you lower training zone(70%) aka fat burner is 157bpm.
Your upper(90%) which you really dont need to do unless you into competition is 182bpm.