What Size AC Do I Need?
Proper sizing for Phoenix homes
Phoenix homes typically need 400-500 square feet per ton of cooling, but many factors affect this. Both undersized and oversized ACs cause problems, undersized can't keep up on hot days, oversized short-cycles and can't control humidity. A proper Manual J load calculation is the only way to determine correct sizing for your specific home.
Quick Comparison
| Factor | Undersized AC | Oversized AC |
|---|---|---|
| Cooling on Hot Days | Runs constantly, can't keep up | Short cycles, high humidity |
| Energy Bills | Higher than expected | Higher than expected |
| Humidity Control | Okay (runs long enough to dehumidify) | Poor (cycles too fast) |
| System Lifespan | Shorter (constant wear) | Shorter (frequent cycling) |
| Comfort Level | Hot spots, can't reach set temp | Uneven temps, clammy feeling |
| Temperature Recovery | Takes hours after opening doors | Quick but doesn't stay cool |
Detailed Breakdown
Undersized AC
- Lower equipment cost
- Adequate humidity removal (runs long)
- Fine on mild days
- Can't keep up on hottest Phoenix days
- Runs constantly, high energy bills
- Shortened lifespan from overwork
- Can't recover after doors open
- Uncomfortable during peak summer
Undersized systems are never ideal. If your AC can't maintain temperature on hot days, it's undersized for Phoenix's climate.
Oversized AC
- Cools quickly
- Easily reaches set temperature
- Plenty of capacity for hot days
- Short cycling damages compressor
- Poor humidity control (clammy feeling)
- Higher equipment and installation cost
- Uneven temperatures room to room
- Higher energy bills from inefficient cycling
Oversized systems are common in Phoenix, contractors often upsize 'just to be safe.' But proper sizing provides better comfort, efficiency, and longevity.
Phoenix-Specific Considerations
Phoenix sizing is not like the rest of the country. Our extreme temperatures and intense sun require different calculations than mild climates.
Forget the "Rule of Thumb"
You may have heard "400-600 sq ft per ton." In Phoenix, it's typically 400-500 sq ft per ton, or less for older homes with poor insulation. A proper Manual J load calculation is essential.
Factors That Affect Phoenix AC Sizing
- Insulation: Older homes may need more tonnage; newer code-built homes need less
- Windows: West and south-facing glass dramatically increases cooling load
- Shade: Trees and covered patios reduce load significantly
- Ductwork: Attic ducts in Phoenix can lose 20-30% of cooling capacity
- Ceiling height: Vaulted ceilings mean more air volume to cool
What Proper Sizing Looks Like
A properly sized Phoenix AC should:
- Run in longer cycles (15-20 minutes typical, longer on hottest days)
- Maintain set temperature except during 115°F+ peaks
- Control humidity effectively
- Provide even temperatures throughout the home
Typical Phoenix Sizing
These are rough estimates, always get a proper load calculation:
- 1,200-1,600 sq ft: 3-3.5 tons
- 1,600-2,000 sq ft: 3.5-4 tons
- 2,000-2,500 sq ft: 4-5 tons or multiple systems
- 2,500-3,000 sq ft: multiple systems
Our Recommendation
Never let a contractor size your AC by square footage alone. We perform a Manual J load calculation that considers insulation, windows, orientation, ductwork, and other factors specific to your home. This ensures you get the right size, not too big, not too small, for optimal comfort, efficiency, and system longevity.
Still Not Sure? We Can Help.
Get a free, no-pressure assessment. We'll give you honest advice, even if it means recommending the less expensive option.