14 CFR §25.929

1. (a)If certification for flight in icing is sought there must be a means to prevent or remove hazardous ice accumulations that could form in the icing conditions defined in Appendix C of this part and in the portions of Appendix O of this part for which the airplane is approved for flight on propellers or on accessories where ice accumulation would jeopardize engine performance.
2. (b)If combustible fluid is used for propeller deicing, §§ 25.1181 through 25.1185 and 25.1189 apply.