Well, I ran software to calculate 1 story with walkout basement ICF 5298 sq.ft.  The program calculated 2 1/2 ton heat pump which is hard to believe.  What about heat strips?  Would 3 ton without strips be crazy.  I did not add any shading inside or outside for the doors and windows  where some of them are shaded.

Air source heat pumps generally aren't very effective at producing heat when the outside temperature drops much below freezing. Going to a larger size heat pump won't do much to change that. That is why you need electric heat strips, assuming you live in an area that gets much below freezing in the winter.

Its in upstate SC where average nigt temp in winter is around 27 or 28. We do have 3 or 4 days whre it dips into the upper teens. That was my thought too about heat strips but they use so much energy that it wasa thought. I believe I will stick with the hvac calc of 2 1/2 tons along with heat strips. Thanks for the reply.

I have used HVAC Calc 4 and previous versions also for a number of years.

I have never had any temp issues using regular and high-velocity equipment; I have not used any of the current available heatpumps so having the backup heat strips is a wise move.

Even GeoThermal systems usually have electric or propane back-up modules for the extremes.