How many btu to heat a 2400 sf home?

Do not go by the basic heat calculation. Have a Hvac company come in and do a heat calc.

They take into account, insulation, wall thickness, Windows, area. This will give you the best size furnace to use.

Ask the company if they use heat calc software, and that you would like a copy of the calc.

This way you know the calc and also that they did not just take the sq ft of the home

and just come close to a #.