I Have a 5 ton trane heat pump with a 42 foot run of duct. The duct starts as a 24x10 for 6 feet, then reduces to 20x8 for 12 feet then 16x8 for 18 feet and then 12x8 for 6 feet. The rooms in the house are all fed from this main duct line and are 5" round ducts. Any thoughts?