We have a new SIPs (Styrofoam) house (6years).
The HVAC contractor ran the numbers and came up with 3 1/2 tons downstairs and 2 1/2 ton upstairs. (3200 ft2) 6"Styrofoam walls and 8" Styrofoam roof. At the time, we did express our concerns about having too much A/C, but the tech explained that with all of the window area etc, that these were the right numbers. I do believe he did due diligence with the calculations for a standard house, but didn't have any kind of a reference for a SIPs house. SIPs houses have VERY few thermal breaks in the insulation (corners only). So an R24 wall is a TRUE R24 for the whole length. VERY airtight.
We even included a fresh air intake as recommended.
Problem is the upstairs unit especially is oversized. South Louisiana, HIGH humidity. Have to set the upstairs on 71 during the summer to be decently comfortable. Downstairs stays on 75.
Both of the units (TRANE), have had the evaporator coils rusted out.
Upstairs after only 5 years, and the downstairs now after only 6 years.
The Trane FSR is maintaining that the units are properly sized but that we need to add a dehumidifier to pull the excess humidity out.
What kind of a recourse or recommended action do you suggest?
Our Trane warranty is parts only for 10 years.