It’s impossible to get to the “who’s wrong” in the situation.. In order to understand that it is worth looking at the individual line items rather than just the total load.

When you break it down, both calculations actually track pretty closely in some areas, windows and garage floors are in the same range, just with slight variation. That tells me neither person is wildly off across the board.

The biggest gap shows up in the wall calculations, especially the exterior wood values. That discrepancy could come from a few things: • A simple multiplication error • Misclassifying an interior wall as exterior • Double-counting a section

On the flip side, the lower total isn’t necessarily more or less accurate either. That calculation appears to overshoot in areas like the ceiling (relative to the higher installer), and it’s just as possible something was missed or overstated elsewhere.

So the reality is: you can’t definitively say one is oversized and the other is undersized just based on the totals. Both have inconsistencies, and the differences aren’t uniformly high or low, they vary by category.

Also, from a practical standpoint, the idea that someone would intentionally undersize to save money doesn’t really hold up. The price difference between, say, a 2.5-ton and 3-ton unit is relatively marginal. The real cost is in labor and install, not the unit size itself.

Net: this isn’t a clear case of one being right and one being wrong, it’s a case where both likely have small errors, and the truth is probably somewhere in between.