WAC 51-11-1302
Space heat type. For the purpose of determining building envelope requirements, the following two categories comprise all space heating types:
Electric Resistance: Space heating systems which use electric resistance elements as the primary heating systems including baseboard, radiant, and forced air units where the total electric resistance heat capacity exceeds one watt per square foot of the gross conditioned floor area.
Exception:
Heat pumps and terminal electric resistance heating in variable air volume distribution systems.
Other: All other space heating systems including gas, solid fuel, oil, and propane space heating systems and those systems listed in the exception to electric resistance.