What size AC unit for 4,500 sq ft in California?8.5 tons
Start with your home and climate. Check the range before a contractor completes your load calculation.
Your starting point
8.5 tons
102,000 BTU/h capacity
Planning range
6.5–10 tons
A screening estimate under the assumptions below. The range is a shopping guide, not a guarantee.
Planning estimate. A licensed contractor must confirm the final size, installation and local code requirements. Electrical work needs a licensed electrician.
Adjust your home
The calculation, step by step.
Floor area x climate-zone screening coefficient x envelope x ceiling height x sun, plus occupants and kitchen heat.
| Input or step | Calculated amount |
|---|---|
| Base cooling | 99,000 BTU/h |
| Envelope / sun / height | 99,000 BTU/h |
| Extra occupants | 0 BTU/h |
| Kitchen | 0 BTU/h |
| Estimated load | 99,000 BTU/h |
What moves this number?
Sun exposure
Heavy shade reduces room-chart capacity 10%; strong sun increases it 10%.
Ceiling height
Screening volume scales with height relative to 8 feet.
People and cooking
Each person beyond two per served zone adds 600 BTU/h; a kitchen adds 4,000 BTU/h.
Your location and assumptions.
Los Angeles, California is IECC 2021 zone 3B. The zone selects a regional screening coefficient. A professional calculation uses local design temperatures and the actual building envelope. Other counties in this state can have a different zone. Local code adoption may use another edition.
- Central HVAC screening coefficients are SizeMyUnit assumptions, not an ENERGY STAR central-AC sizing rule.
- 1 ton = 12,000 BTU/h. Capacity rounded upward in half-ton steps.
- +/-20% shopping band is not a confidence interval.
- 8 ft ceilings, moderate sun, 2 occupants
What might it cost to run?
Illustrative full-load cooling cost: about $2.72/hour at an assumed EER of 12 BTU/Wh (8.50 kW). Actual efficiency, cycling and fan power differ. Uses the published 2024 EIA California residential average of $0.3197/kWh, not your current tariff.
Before you choose equipment.
Oversizing can reduce humidity control and comfort. Manual J determines loads; Manual S selects equipment; Manual D sizes ducts.
This large served-area result can require multiple properly designed zones or units. Do not select a single oversized unit from the total alone.
Bring this calculation to your installer. They will check the measured load, manufacturer performance, distribution or connections, installation conditions and local requirements.
A few more sizing questions.
What size AC unit for 4,500 square feet?
The default screen gives 8.5 tons, with a planning range of 6.5–10 tons. Change the inputs above to reflect your actual home.
How many BTU are in one ton?
One ton of cooling equals 12,000 BTU per hour. The estimated load here is 99,000 BTU/h; an equipment nameplate is a capacity rating, not electricity consumption.
Should I choose a larger unit just in case?
Excess capacity can cause short cycling and poor humidity removal. Use the range to discuss uncertainty, then select using a professional load calculation and manufacturer data.
How do sun and ceiling height affect the answer?
Shade uses a 0.9 multiplier and strong sun 1.1. This screen scales ceiling height relative to 8 feet. The sun adjustments come from ENERGY STAR room guidance; height scaling is our assumption.
Can one room unit cool the whole house?
The served area needs air circulation and a suitable layout. Closed bedrooms, multiple stories and separate zones cannot be sized as a single open room. Mini-split heating needs a separate winter capacity check.
Is this a final equipment size?
No. A licensed contractor must measure your building or actual loads, check manufacturer performance and local code, and confirm the final selection.