I've had a load calc completed by two competent HVAC companies and have two quotes but I'm receiving different stories from them concerning their systems and my duct work.
My existing system is a 20 year old Trane XL900 heat pump with a 7 year old 3.5 ton American Standard Air Handler (AH). My trunk line is flex and about 40 foot long. The AH is in the attic. I live in south Ga and it is hot and humid here. The air flow seems ok at the fartherest line but I'm sure more would be better.
Quote A: 3.5 ton Carrier Cond #25HCC542A003, VS AH # FV4CNF005T00, with a Thermidistat. He states his sytem will do a fantastic job of controlling humidity as well as temperature. However, he says I need to get rid of my existing flex trunk line and replace it with pipe for it to work correctly. His price for the system is comparable to the Trane below...but the extra cost for the duct work puts him much higher than the Trane.
Quote B: 3.5 ton Trane Cond # 4TWR5042E, VS AH # 4TEE3F65. Originally he had a non-programable Tstat in the quote but when I told him I wanted to have humidity control he quoted the Trane TCONT800 and said it would give me the himidity control I'm looking for. He stated, "it's all in the Tstat". He states my existing duct work is fine and no changes are needed.
My questions are:
1. Would changing out the flex trunk line to pipe be a huge difference in air flow at the fartherest register?
2. Which system above will give me the best humidity control? My son is allergic to dust mites and I want to be able to keep the humidity below 50% to kill the dust mites.
3. Which system is going to be most efficient?
Thank you very much for your assistance!