How many BTUs do you need to heat and cool a 2,000 square foot house?

What climate zone is the house in? How much insulation does it have? How tall are the ceiling - open beam, 10', 8 ' ???

You should search a tool usually found on the website of reputable mfgs of heating and cooling like rheem, trane etc. for their calculators. Consider cubic area, not simply square feet. Also, what is the heating source available to you? Natural gas? electricity? Propane? Hot water/boiler?

I'm in CA. The requirement along the southern CA coast is vastly different from the requirement in the Eastern Sierra Nevada mountains of Mammoth Lakes CA or Lake Tahoe etc.

Too many variables to guess: climate, aspect and surroundings, insulation type, placement and thickness, air infiltration rate, how the house is used (kept warm 24/7 for the elderly in winter, or kept cool and everyone wears sweaters), etc.

Roughly about 48000 or 4 ton but it depends on the insulation values of the home and area of the country your in. You need a local hvac contractor to tell you.

Depends on how well it's insulated, and what kind of climate you're in. No one can say for sure without that info.