Stop Guessing Your
HVAC System Size.
Oversized units can leave your home humid. Undersized units may struggle on the hottest and coldest days.
Use our Zip-code based Manual J-inspired estimator to get a realistic starting point for the Tons & BTUs your home is likely to need.
Why "Rule of Thumb" Sizing Fails
Many contractors still use the old "500 sq ft per ton" rule. For modern, code-built homes with better insulation and windows, this rule of thumb often leads to oversized equipment.
According to guidance from the Air Conditioning Contractors of America (ACCA) and building-science research, oversized AC units can:
- Short Cycle: Turn on and off too frequently, wearing out the compressor.
- Fail to Dehumidify: They may cool the air faster than they remove moisture, leaving your home "clammy."
- Increase Bills: Frequent startup and shutdown cycles increase energy use.
How This Manual J Calculator Works
A true Manual J calculation requires detailed room-by-room data (construction, windows, orientation, infiltration, and more). Our simplified tool bridges the gap for homeowners by focusing on the 4 largest drivers of load:
📍 Local Climate
We use your Zip Code to pull typical cooling degree days (CDD) and design temperatures for your region.
🏠 Insulation Age
Older homes with original insulation and windows can need 20% or more heating and cooling capacity than similar newer homes.
Pro Tip: If your estimate falls between equipment sizes (e.g., 2.7 Tons), look for equipment whose total cooling capacity is within about 10–15% of your calculated load, in line with ACCA Manual S guidance, instead of automatically rounding up. For variable-speed inverter units, aim for the closest available size to your calculated load.
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