Thanks for your responses Magoo and Ranger1. Speaking of refrigerants, what do you think about CO2/NH3 cascade systems? Pros and cons? My limited knowledge which stems from researching on the web seems to point to CO2 as the refrigerant of the future. Some articles also claim that installation costs/equipment will be cheaper (for one, because of smaller pipe diameters?) than pure NH3 although operating costs are about the same. Is this true? Some people then claim that CO2 is only cost-efficient at really low temps like -40 degrees celsius. Any comments?