After all is done and said, this is a thermodynamic problem.
-What is the fan’s airflow and under what static pressure?
-What is the heatsink’s thermal resistance, with the calculated airflow?
-What is the heatsink’s ambient temperature?
-How many calories, joules, BTUs (or whatever thermal unit you wish to use) is the peltier module rated for? How does that compare to your thermal load?
-What are the peltier’s losses, which the heatsink will also dissipate?