I just want to say that this site is fantastic!
OK, on to the question....
I have a 30 year old single Carrier 3 ton split A/C system. I live in a 2000 sqft., 3 level town home of the same age. The AH is located on the middle level. The duct work is all hard line. The first level is just an entrance with stairs and an exit to the garage, but for informative purposes I will count it as a level. It does have a vent going to it.
I had an estimate from an HVAC tech that came highly recommended from numerous people. When I asked him about doing a Manual J, he said I didn't need it. He said to just replace the old unit with a new unit of the same tonnage. (Is that a word?) He want's to replace the AH too, which is fine.
Now I've done some fairly extensive changes to my town home. I've knocked out walls, replaced appliances and done some electrical and plumbing. One thing I've learned in doing this is that the hippie contractor that built my place did it as cheap as possible and all appliances and most of the workmanship were bottom of the line CHEAP! So I'm assuming that his choice in A/C systems was inspired by the same line of thought. I know my A/C unit is inefficient. But I also theorize that the A/C unit is under tonned because it was cheaper. My place is never comfortable in the extremes of the seasons.
I suggested again to the contractor that maybe we should do a Manual J to see if my home is under tonned and he still refused saying that the duct infrastructure is built to handle 3 tons and no more. If I went up in tonnage (there's that word again) then I would have to provide more duct sqft. to accommodate the larger ton capacity. Is this true? Or is it a good thing that I'm asking this question on the forum?
Thanks so much for your help and advice.