Case Study: A 2000 Sq Ft Home in 3 Different Climates
Here's a question that illustrates why "500 sq ft per ton" is so dangerous: What size AC does the same house need in Phoenix, Miami, and Chicago? The answer will surprise you.
We're going to run a hypothetical through our load calculator. Same house, same square footage, same insulation, same windows — but three different climates. The results show why climate-specific data is critical for HVAC sizing.
The Test House
- Size: 2,000 sq ft, single story
- Insulation: Built 2010, average insulation (R-38 attic, R-13 walls)
- Windows: Double-pane, low-E, ~150 sq ft total
- Ceiling height: 8 ft standard
- Orientation: Typical suburban lot, mixed orientation
- Occupancy: 3 people, typical appliances
Scenario 1: Phoenix, Arizona (Hot-Dry)
Phoenix represents one of the most extreme cooling climates in the US. Design temperature: 108°F. Cooling Degree Days (CDD): 4,500+.
Phoenix Results
- Summer Cooling Load: ~48,000 BTU (4 tons)
- Winter Heating Load: ~35,000 BTU
- Primary concern: Extreme heat, moderate humidity (latent load manageable)
- Equipment recommendation: 4-ton AC or heat pump; 60,000-80,000 BTU furnace
Note: Phoenix homeowners often add 0.5-1 ton to account for poor ductwork in tile-roof homes. Our calculator assumes reasonably efficient ducts.
Scenario 2: Miami, Florida (Hot-Humid)
Miami represents the opposite extreme — high temperatures AND high humidity. Design temp: 91°F, but wet bulb: 78°F.
Miami Results
- Summer Cooling Load: ~42,000 BTU (3.5 tons)
- Latent Load: HIGH — humidity dominates
- Winter Heating Load: ~15,000 BTU (minimal)
- Equipment recommendation: 3.5-ton variable-speed AC for better dehumidification; heat pump for heating (very low heating load in South Florida)
Despite similar temperatures to Phoenix, Miami needs LESS total cooling capacity because the air is already cooler (wet bulb is the key). BUT it requires BETTER dehumidification — a variable-speed unit is strongly recommended.
Scenario 3: Chicago, Illinois (Cold)
Chicago is a heating-dominated climate. Summer cooling is moderate; winter heating is extreme. Design temp: -4°F. HDD: 6,000+.
Chicago Results
- Summer Cooling Load: ~36,000 BTU (3 tons)
- Winter Heating Load: ~75,000 BTU
- Primary concern: Heating dominates — you need a large furnace or heat pump with excellent cold-weather performance
- Equipment recommendation: 3-ton AC or dual-fuel heat pump; 80,000-100,000 BTU furnace OR cold-climate heat pump
Chicago needs the LEAST cooling but the MOST heating. A heat pump alone would struggle at -4°F unless it's a cold-climate model. A dual-fuel system is ideal.
The Comparison
Same House, Three Different Requirements
| Climate | Cooling | Heating | Recommended System |
|---|---|---|---|
| Phoenix (Hot-Dry) | 4 tons | 35k BTU | 4-ton AC + 60k furnace |
| Miami (Hot-Humid) | 3.5 tons | 15k BTU | 3.5-ton variable-speed + heat pump |
| Chicago (Cold) | 3 tons | 75k BTU | 3-ton AC + 80-100k furnace OR dual-fuel |
Key Takeaways
1. Cooling Capacity Varies by 33%
From 3 tons (Chicago) to 4 tons (Phoenix) for the same 2,000 sq ft house. That's a full ton of cooling difference — thousands of dollars in equipment and installation.
2. Heating Requirements Vary 5x
Miami needs ~15,000 BTU for heating. Chicago needs ~75,000 BTU. This is why heating equipment should ALWAYS be sized based on a heat load calculation, never on cooling size alone.
3. Humidity Matters as Much as Temperature
Phoenix and Miami have similar dry-bulb design temperatures, but Miami's high humidity requires better dehumidification capability. A single-stage unit would struggle in Miami; a variable-speed unit is strongly recommended.
4. One Size Does Not Fit All
If a contractor from Chicago tried to sell the same HVAC system they install in Chicago to a Phoenix homeowner, one of them would be wrong. And it's usually the homeowner who pays the price.
The Bottom Line
Your zip code matters. Local climate data — design temperatures, humidity, cooling and heating degree days — directly determines what size HVAC system your home needs.
This is why our calculator asks for your zip code: we use your local climate data to produce a load estimate specific to your location, not a generic rule-of-thumb number.
Run your own home through our free load calculator with your actual zip code to see what your climate-specific load really is.
Get Your Climate-Specific Load
Enter your zip code to see exactly how much cooling and heating capacity your specific climate requires.
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