A counterflow heat exchanger includes a first fluid inlet, a first fluid outlet fluidly coupled to the first fluid inlet via a core section, a second fluid inlet, and a second fluid outlet fluidly coupled to the second fluid inlet via the core section. The core section includes a plurality of first fluid passages configured to convey the first fluid flow from the first fluid inlet toward the first fluid outlet, and a plurality of second fluid passages configured to convey the second fluid flow from the second fluid inlet toward the second fluid outlet such that the first fluid flow exchanges thermal energy with the second fluid flow at the core section. One or more drains are operably connected to the plurality of first fluid passages configured to remove condensation from an interior of the first fluid passages prior to the condensation reaching the first fluid outlet.