I wish I still had the info from my laptop. I took the local temps and did my own calculations to come up with what man j uses. It was quite a bit different than the published temps they have. Here the book design temp is 99*. When I ran the local temp data it was 105*. Which is why so many houses here are hot in the summer. It's very common to up size units on relativly new houses. A friend of mine does quite a few. Also some city's have started to spec design temps that are higher than in the man j calculators as they know they are off.
As for the muggy days in the 80s. Well here there are so few that it doesn't matter. It goes from nice and the windows open to mid 90s like a light switch then summer gets here and it's over 100* for 8 hours a day with highs up to 117 some summers and often for weeks on end with those highs.
Man j is a great tool but you have to keep a skeptical eye on it and don't believe the numbers provided are correct for your locality. It even says as much in its own documntation.
Our old system was a 3 ton (dying compressor)/100k furnace which just wasn't enough in the summer. The new one is a 3.5 ton 16 seer with a 100k two stage furnace 96%. Should be a night and day difference this summer. I also had to move 3 registers. The one in the kitchen and dining room were in really bad spots and there was only one in the living room. They didn't understand much about airflow in 1960 or leikely didn't care...
What still surprises me is the gauge of the wire on furnaces now. They are using 18 ga wire from the j box in the unit to the board. That means a max current of about 8 amps. Much lower than the older models. The efficiency increases have made quite a difference in amp draw. Also the change to scroll from recip compressors. However I would have gone with a lower seer as we will be moving. Higher seer doesn't help home value and spending more on super high seer units never pays back unless your Elec is super pricey or you are solar.
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