How to Size an HVAC in a Superinsulated House

A common method of estimating the proper size for your heating, ventilation and air conditioning unit, sometimes referred to as HVAC, is the square footage method. You need a 12,000 BTU room air conditioner, roughly equivalent to the old 1-ton description, to cool an area of between 450 to 550 square feet, according to the U.S. Department of Energy's EnergyStar program. You also need to consider other factors when sizing a superinsulated house for an HVAC unit, however.

Instructions

- 1
  Determine the square footage of the living space in your home. While this is not the only factor in determining the proper size for your HVAC, it is one important factor that must be considered. You can figure your home's square footage by multiplying the length times the width of each room and adding the results together.
- 2
  Determine your heat loss factor. Measure your levels of insulation. A superinsulated house will have minimum insulation levels of R-24 in the walls, R-40 in the ceiling and R-19 in the floor. A superinsulated house should have tight-fitting windows with double-pane glass, vapor barriers to prevent the migration of heat and air, and an excellent drainage system to keep the foundation dry and free from mold. The heat loss factor for a superinsulated house ranges from 21 to 25 BTUs per hour per square foot, according to the Old House Web website.
- 3
  Multiply the total amount of square footage in your home by both the lower and upper ranges of your heat loss factor to determine a projected size range of an HVAC unit for your superinsulated home. Keep in mind that this is a rule of thumb only, and will give you an estimate of the size you need. Your HVAC contractor should perform exact calculations using formulas provided in the Air Conditioning Contractors of America Manuals J, S and D to determine the proper size HVAC for your home.

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