I will be replacing a carrier 2.5 packaged heat pump with a rudd 3.5 ton packaged heat pump due to an addition to our house of 420 extra square feet. I have decided to switch brands due to the poor performace and troubles I have had with the carrier - recent problem - leak on inner coil which is rather expensive to have replaced. Unit is only 6 years old. An additional return will be added to the new addition - currently only have one return. I have two (2) questions. The model number of the rudd I am getting is RQMJ-A042JK010 12seer 3.5 ton packaged heat pump. Does this seem to be a good unit if properly installed. 2nd question. They will be installing a y to the existing flex duct on the existing return and running to the new return. The current return has 14 inch flex duct running to the unit. Is this large enough or does this need to be increased in size. I have had someone tell me this is not large enough and could possible 'starve' the unit for air?? The current trunk line is 14inch. They will be increasing this to 16 inches for the first 12 feet comming off the unit. All comments / help will be greatly appreciated.