Consistantly HIIT workouts, either produce significant EPOC statistically, but not practically significant, or do not reach significance at all.
In our lab, we have done 3 EPOC studies over the last 3 years. One I was co-investigator on last year and it analyzed the EPOC response to interval training for 30 minutes in females. We worked them so hard that they were near fainting, with one participant actually fainting!
While our results nearly reached statistical significance, they fell short. Further, practically even though 02 consumption was elivated, it literally did not have any practical significance.
We then analyzed the comparison of the interval training to resistance training and found no significant difference between the two in EPOC.
In addition weight training is high intensity training, and would produce similar if not greater effects on EPOC then interval or HIIT training. Therefore, if you weight train already, you are really already incorporating a form of HIIT, at least in terms of the muscle fibers stimulated, temperature changes, and hormonal response, which are what causes HIIT.