About loadcalc a load calculation program based on manual j designed to be quick and easy to use it calculates the amount of heating and cooling btus needed for the whole house block load or a room by room load. Load calculationa systematic method of evaluation to estimate heat loss sensible and latent heat gain an account of the total heat flow into or out of a home depending on the time of year we need to do load calculations in order choose equipment that will make an occupant comfortable and safe and to keep energy costs down. To calculate the estimated hvac load for a house with 2500 square feet 12 windows and 3 exterior doors occupied by 4 people simply plug it into this formula 2500 x 25 62500 base btu 4 people x 400 1600 12 windows x 1000 12000. Our enhanced manual j load calculator is now powered by cool calcs innovative software this dynamic integration lets you create fast efficient acca approved reports that comply with national design standards and meet building code requirements best of all our manual j load calculator is free through lennoxpros