I just had my 1st floor ducts replaced(old one were 60 years old). I have a 2 ton Lennox system(1900 Sqft 1st level, seperate system on level 2), the central return is 26 X 8 rectangle metal duct. About a 20 foot run with one 90 deg turn. The return floor opening is 30 x 8. Is this enough or should I have an additional return installed? Currently I wouldn't say the return is loud, but it is certainly not quiet Thanks.