Why your Spokane AC is probably oversized (and what to do about it)
If your Spokane AC system is 15+ years old, there\u2019s a good chance it\u2019s oversized by 1\u20132 tons. That hurts comfort, hurts efficiency, and shortens equipment life. Here\u2019s why — and what to do about it.
Devon R.
Tech Network Manager, NATE-certified · June 22, 2025 · 7 min read
Quick answer
AC sizing in Spokane is based on Manual J load calculation, not square footage. A 1,800 sq ft Spokane home with average insulation typically needs a 3-ton (36,000 BTU/hr) AC, but can vary from 2.5 to 4 tons depending on orientation, window area, and duct leakage. Right-sizing matters because oversized units short-cycle (high humidity, poor dehumidification) and undersized units run constantly (high utility bills, no rest cycles).
- Manual J load calculation required for proper sizing.
- Spokane cooling load range for 1,500–2,000 sq ft: 24,000–48,000 BTU/hr (2–4 tons).
- Square footage rules of thumb are 20–40% inaccurate.
Bigger isn\u2019t better when it comes to AC. Most Spokane homes are 1\u20132 tons oversized. Here\u2019s why that hurts comfort, efficiency, and equipment life.
The rule-of-thumb sizing problem
For decades, HVAC contractors sized residential AC using rule-of-thumb formulas: 1 ton per 400–600 sq ft. A 2,400 sq ft home got a 4-ton or 5-ton system.
The problem: those formulas ignored insulation quality, window efficiency, orientation, ductwork, and air infiltration. A 2,400 sq ft home with good attic insulation and modern windows needs about 3–3.5 tons. A 2,400 sq ft home with poor insulation and original windows needs about 4–4.5 tons. The rule-of-thumb gave both homes the same equipment.
Most Spokane homes were oversized using this method.
Why oversized is worse than undersized
An undersized AC runs constantly but keeps the house cool. An oversized AC cools the house fast, then shuts off — short cycling.
Short cycling is bad for three reasons: (1) it doesn’t run long enough to dehumidify, leaving your house feeling cool but clammy, (2) it cycles the compressor on and off repeatedly, which is the #1 cause of premature compressor failure, and (3) it uses more electricity per unit of cooling because startup draws are higher.
The result: clammy house, higher bills, AC that dies 5 years too early.
The Manual J solution
Manual J is the ACCA-approved calculation for residential cooling load. It accounts for: climate (Spokane’s design temp is 91°F), home size and orientation, insulation R-values and area, window U-values and SHGC, air infiltration rates, internal gains (appliances, occupants), and duct leakage.
A proper Manual J takes 30–60 minutes. The tech measures attic insulation depth, inspects window condition, evaluates ductwork in unconditioned space, and runs the calculation in software.
The output is a precise cooling load in BTU/hour, which translates to the right equipment size. For most 2,000–2,500 sq ft Spokane homes, that’s 3–3.5 tons — not the 4–5 tons a rule-of-thumb would suggest.
What this means for your install
If you’re replacing AC, demand a Manual J. If the contractor doesn’t want to do one, find another contractor.
We run Manual J on every AC install quote — no charge. It’s built into the quote visit because the right answer depends on the calculation, not the rule-of-thumb.
The cost difference between right-sized and oversized is typically $0–$1,000 (smaller equipment costs less to buy). The comfort and efficiency difference is significant.
Manual J is one of those industry standards that\u2019s been around for decades but routinely skipped. Any contractor worth hiring will do it without being asked. If yours won\u2019t, that\u2019s a signal.