I forget the exact figure but I believe that a certified CH system must be able to raise the temp by 70 + (?) degrees (F). This should allow for the removal of ice and preclude the formation of ice under any conditions. The danger is that CH may raise the temp in the venturi to within the icing range relates to the use of PART heat not full heat , hence the usual all or nothing advice (if no reliable CAT is available). In any event colder air holds less moisture so the risk will be reduced..