Am replacing a 28 year old Carrier (38EB030300) heating and cooling system. Stills cools and heats but it's time. The Carrier is a 2.5 ton and handles the main floor and downstairs finished (heated and cooled) basement & office. The mainfloor is around 1200 sf and the downstairs around 500 sf. Above the mainfloor, upstairs, are the bedrooms, which are handled by another 2.0 ton Carrier system.
The upstairs has never been a problem with heat or cooling. The mainfloor has always been difficult to cool on hot days. Normally, I leave the thermostat at 77-78. The house is surrounded by trees so there's plenty of shade. Four normal size windows on mainfloor face West and get afternoon sun.
I've gotten 5 different estimates from different contractors. Three suggest a 3.0 ton unit and two say a 2.5 ton is enough. One contractor explained that 2.5 tons is enough because the mainfloor is 1200 sf, and there is another heated and cooled floor above and one beneath, and the basement, around 500 sf, does not need that much cooling capacity. Another contractor explained that 3.0 tons should be put in because a little too much (.5 ton too much) is better than not enough, and the only time too much is a problem with cycling is when there is way too much (e.g., 1 ton too much).
Both contractors are offering Lennox units. The one proposing 3.0 tons is actually less money.
I know there are other factors involved, but from this information, can someone please offer an opinion as to what size should I go with, 2.5 ton or 3.0 ton?