I used the HVAC-Calc softeware (HOMEOWNER VERSION). It took me a little time but I now know that the exsiting 3 ton unit is the approriate size for my home. I had two additional sales reps come to my home to give me estimates. They both initially said my existing unit was too small. When I showed them print out of the load calculation they seemed surprised by the results. I've had three company's out of 8 give me quotes for the correct size unit. I am going to call them back and see if I can set up another appointment. I have some additonal questions based on the advice I have recieved on this forum. I don't know how often you all are thanked for your advice, but I wanted to say Thank You! Now all I have to do is decide on which brand and which company. I'll keep reading!!!