Thanks to all who have commented on my previous post about seeking Unico proposals for adding air conditioning. In reviewing 3 proposals, the only remaining issue for me is a discrepancy in the load calculations/recommended size unit by the low cost proposer. Here's the house description:
Small 2 bedroom slab-on-grade home which has radiant in-floor heat. Upper Midwest, 1 mi. from a Great Lake. Main house is 890 SF: Living/Dining combined and Kitchen face east, Kitchen is on southeast corner; on the west side, the Bedrooms flank one Bath and central Hallway/Attic access. Utility room 130 SF is attached on south, access door from Kitchen is often closed. Garage attached on south side of Utility. Large east windows at Living and Dining and Utility. Seasonal canvas awnings limit solar gain on Living, Dining, and Kitchen. House is clad in stone, together with the concrete slab it tends to provide a stable environment. Attic insulation is original mineral wool plus 3 1/2" batt for total ~6", some additional batts around eaves; exterior walls 3 1/2" batts; windows mostly original single-pane with new wood storms, 3 large windows on east side are Thermopane. I've been using one inadequate small window air conditioner, I usually keep many of the wood storms on in summer to protect the old wood windows; during moderate temperature, ventilation is through screen doors and kitchen screens, that's adequate.
The lowest cost proposal recommends a 1.5T unit, I asked this contractor to double-check in light of the other two proposers recommended between 2.0T and 2.5T (depending whether the Utility room is served or not). The low proposer says they checked with a second engineer and stand by their 1.5T recommendation regardless of whether future home owners use awnings or not, tree shading is reduced, etc. This contractor states they are Unico certified trained. I am seeking references from them to check out.
I certainly do not want to pay for more capacity than is necessary, I am leaning towards accepting the 1.5T if their references check out, the fact that this house's environment tends to be stable if rapid temperature swings are avoided (esp. solar gain through windows) is an important reason why I tend to favor their recommendation, plus proximity to lake. Comments, opinions welcomed, thanks.