We have a 1550 sq ft walkout ranch in West Michigan, currently basement is unfinished, looking to finish in the near future. It would add two bedrooms, bathroom and very good sized lower great room (550 sq ft). Total finished in the basement would be about 1100 sq ft. It has nine foot ceilings, slider, two large picture windows and a couple smaller 30 in windows. Currently it is cold down there, bare concrete floor (believe it is insulated below) concrete walls are mostly insulated, only R-6 and stud walls are insulated R-15. I will insulated any bare concrete that remains, plus add r-11 to the walls when I stud the concrete. There are two HVAC vents currently at the ends of each trunk and it does not get warm. I know two vents wouldn't be able to warm it, just not enough CFM.
My question: Should I spend the extra money to have a zone in the basement? I haven't had anyone come out and quote yet but I do know some HVAC guys and one says it shouldn't need to be if setup right, and the other says being nine foot ceilings with the windows and slider it should be zoned.
What are you suggestions from past experiences?