Keep in mind equipment design and load calculations when choosing a heating or cooling system.
(The following is taken from the Sheet Metal and Air Conditioning Contractors' National Association's Residential Comfort System Installation Standards Manual.)
All heating or air-conditioning equipment should be selected on the basis of its Btuh (British thermal unit per hour) output, air-handling capacity, pumping capacity and thermal-transfer capability to handle the calculated design-heating or air-conditioning load. Energy-conservation legislation has led to the selection equipment sizes that are adequate for the tasks, but not oversized. All equipment must meet the requirements of ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) Standard 90.2, "Energy-Efficient Design of New Low-Rise Residential Structures," and other local codes.