Carburetor Heat Required on Carburetor equipped GA aircraft?
Carb heat is not specifically required by regulation. What is required by the following rule is a means to prevent ice accretion:


  14 CFR 33.35 Fuel and induction system.
  
  (b) The intake passages of the engine through which air or fuel in
  combination with air passes for combustion purposes must be designed
  and constructed to minimize the danger of ice accretion in those
  passages. The engine must be designed and constructed to permit the
  use of a means for ice prevention.


Carb heat is the most common solution, but alternate solutions may be acceptable.