Originally Posted by
Rodney28334
Adding to what George said, I would like to see more than 7 - 8" flex returns for a 3 1/2 Ton, especially with a furnace (to save heat exchanger). The main issue is how the flex is tied into the return duct. He said in a previous post you said it was all flex, but there is some metal ducting somewhere, be it a square/rectangular plenum, or a branch duct setup. I am going to Over simplify this. I like to have a larger central return and a few smaller ones for big bedrooms, bonus rooms, ect. But if I was going to run just 1 large return for a 3 1/2 Ton. 1- 18" metal pipe has a area of 254 sqin, a 8" round pipe has area of 50 sqin. 7x50=350 sqin. I dont know what model you have but lets assume it has a 20"x20" return opening. 20x20=400 sqin. We are ignoring friction loss for this scenario but with it being flex and several small returns in real life it cant be overlooked. Assuming the duct is adaquite size the situation may not be as bad as you think. Is this new construction or a changeout/remodel. You can have the company come out and check the duct pressure or if you do not trust them have another company do it. Also if this home is older and not had any/many renovations it may not be grossly oversided depending on other factors, and the efficiency of furnance.