I just had a ac installed recently. The unit is a 3.5 ton air handler with a 4 ton condenser. The air handler has 22x24 return opening and my return air grill is 20x24. My contractor agreed that my return is slightly undersized but due to the tight area (no room to expand it between the trusses) he said it was not a problem because the return was drawing air silently and the static pressures were fine. He said it does hurts my efficiency slightly but not enough to actually be concerned about. I've done a Manual D calculation and I have 480 sq ins but I calculate I need 576 if I want 350 fps air velocity and that's not even adjusted for grill free area. My question is....Is he right that I shouldn't worry about it if my return is quiet (which it is) or is there something else I should be worrying about?
Oh yeah, def a typo. fps is for bullets not air velocity lol. The return air duct is only about 8 ft long. Could you give me some insight as to why the recommended return size is so large? Is sound the only reason?
Sorry didn't read fully, 18" duct with no 90 turns just a long sweep and I live in South East Florida