The fact that a reaction needs to be heated doesn't mean that it is endothermic. For example, the combustion of gasoline is very exothermic. However, the combustion (thankfully) occurs very slowly at room temperature. You need to add energy in the form of heat or a spark in order to get the reaction going (i.e. achieve a reasonable reaction rate).
Additionally, the dissolution of salts like ammonium chloride occurs very quickly at room temperature despite the fact that the process is endothermic. So, the thermodynamics of a reaction are not immediately applicable to the kinetics of a reaction.