If there is not too much water inside, the furnace heat will dry the duct anyway. 7 d+ n9 n. L0 ?8 x/ _1 a3 T! w5 t& A5 v( A. B! x) S4 a
But if there is lot of water inside the duct, most water will go somewhere in the house. Then it will grow mold over there in few days. You need to find out where the water goes and clean out as soon as possible.