A heater including a housing, a first tankless heater, a second tankless heater, a first and second flow directing elements, the first flow directing element in communication with the first tankless heater and the second flow directing element and the second flow directing element in communication with the second tankless heater, and a controller in communication with the first and second tankless heaters and the first and second flow directing elements, the controller configured to control the first and second flow directing elements to control flow to one or both of the first and second tankless heaters.