Load Calculation
The engineering math that determines how much heating and cooling your specific home needs, from measurements, insulation, windows, air-sealing, and orientation. See Manual J — the industry-standard method. Skipping it is how systems end up over- or undersized.
The longer answer
A load calculation measures your home's heat loss (winter) and heat gain (summer) based on actual construction — wall area, window type, insulation depth, air leakage, orientation. The result is a BTU/h number that equipment must match, not exceed.
Square-footage rules of thumb ('1 ton per 500 sq ft') are how systems get oversized by 30–50%. An oversized system short-cycles, creates temperature swings, and under-dehumidifies in summer. Every honest bid starts from a load calculation or an equivalent room-by-room assessment.
The Seattle angle
In Seattle's mild climate, load calculations often produce smaller equipment than homeowners expect — right-sizing is the single biggest comfort and efficiency lever on any install.
Guides that use this term
Heating · Learn
Why does my furnace keep turning on and off?
Air Conditioning · Learn
How do I get my Seattle home ready for the next heat wave?
Air Conditioning · Learn
What size AC does my house need — and why isn't bigger better?
Ductless Mini-Splits · Learn
Why is ductless the go-to for Seattle's older homes?
Heating · Evaluate
How do I actually compare HVAC quotes?
Where this decision happens
Nearby in the glossary
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