Before you install a new air conditioning system, consider your home's electrical system. It's not uncommon for old houses to have only 110-volt, 60-amp service for the entire home, barely enough power to handle the home's existing complement of lights and appliances. Central air conditioners require a dedicated 230-volt circuit and may require 20 to 50 amps of power, making an electrical service upgrade necessary. Have an electrician size your home's electrical supply up before your HVAC contractor begins work.
The use of ridge vent has increased greatly during the past ten years and when used with a soffit vent or vented drip edge, it is a very effective means of venting rafter bays, especially in cathedral ceiling areas. An air space in the rafter bay must be provided for full airflow. There are various styrofoam vent channels that, installed in the rafter bay, keep the insulation from fully filling the bay, to allow for air space. This can help keep condensation from forming on exposed roof nail ends and dripping onto the ceiling materials below during winter months.