I apologize because I forgot to add this on to my last question, but I've noticed all over the forum that it's almost a universal recommendation from you pro's to make sure my contractor does a load calculation and measures the duct work in my house to ensure they're selling me on the correct sized system.
I've had 4 of the more reputable companies out for bids and not one of them has done this.
Is it something I should have to ask them to do, or am I calling the wrong companies?
I have a basic 35 year old ranch in the midwest, and these guys typically just look at my old equipment to make their decisions on deciding what to offer me.
Can it be they've done it so long it's second nature and easy for them to tell?
This is the last heat and AC I hope to buy so I don't want to kick myself for the next 15 years because I made a mistake.

Thanks for any advice.