BTU suggestion for 3000.sq ft home

There really is no such thing as a suggestion for HVAC.

You need to do a manual J to see exactly how many BTU's you will need.

If you are replacing the duct you will need to do a manual D to get the correct sizes etc.

Search Google for information referred to above. OR use the link below

MrHVAC.com Heat Gain and Loss Short Form Load Calculator (http://www.mrhvac.com/loadcalcshortform.htm)