What the work is
A load calculation works out how much heat your house actually gains and loses: its orientation, its glass, its insulation, its air leakage, its ceiling heights, room by room. It is the difference between sizing a system for your house and sizing it for its square footage.
Oversizing feels like the safe choice and is not. A system too large for the load cools the air quickly, satisfies the thermostat, and shuts off before it has removed any humidity. You get a house that is cold and clammy, equipment that short cycles, and a compressor that wears out early.
You can have the calculation whether or not you buy the system from us, and you can take it to anyone else.
What goes into it: the orientation of the house, the area and type of every window, the insulation in the walls and the ceiling, the infiltration rate, the ceiling heights, the shading, and the number of people. The output is a heat gain and a heat loss figure for every room and for the house as a whole.
The room-by-room part is what makes it worth having. A whole-house figure sizes the equipment; the room figures tell you which rooms the ducts are failing to serve, and that is usually the actual complaint that started the conversation.
What is included
- A measured survey of the house, not a rule of thumb
- The room-by-room result in writing, and yours to keep
- What it means for the equipment size, in a sentence
- Window areas and orientation measured, not estimated from a floor plan
What is not
- Sizing from the label on the old unit, which is how the old one got its size
- Sizing from square footage alone
Why the number matters more here
St. George recorded 98 days at or above 100°F in 2024, the most on record, and the all-time high is 117°F. A system sized for a mild place is not sized for this one.
Design load is worked out against the temperature the house actually sees, and here that is a long way from the national default. It is also why a rule of thumb carried in from somewhere else lands wrong in both directions.
What to ask anyone quoting this, us included
- Was a Manual J done, and can I have a copy?
- What size did it come out at, and what size are you quoting?
- If those differ, why?
- Is this room-by-room, or whole-house only?
- What did you assume about my insulation, and did you check?