Manual J Case Study: Hot Climate vs Cold Climate HVAC Sizing
Location, Location, Location. How geography dictates your heating and cooling equipment.
You cannot just take floor plans from one state and build them in another without changing the HVAC system.
In this case study, we explore hvac load by climate zone design. We'll take the exact same 2,500 sq ft house plan and "build" it in two extreme locations: Phoenix, Arizona (Hot-Dry) and Minneapolis, Minnesota (Cold).
The Design Conditions
Manual J calculations start with "Outdoor Design Conditions." This is the temperature that represents the 99% worst-case weather for that city.
Phoenix, AZ (Zone 2B)
- Summer Design Temp: 108°F
- Winter Design Temp: 34°F
- Delta T (Summer): 33°F difference (108 - 75 indoor)
- Challenge: Extreme sensible heat gain.
Minneapolis, MN (Zone 6)
- Summer Design Temp: 88°F
- Winter Design Temp: -15°F
- Delta T (Winter): 85°F difference (70 - (-15) outdoor)
- Challenge: Extreme heat loss.
Hot Climate HVAC Sizing (Phoenix)
In Phoenix, the battle is against the sun. The manual j climate zones data shows massive solar gain.
The Load:
Cooling Load: 42,000 BTUs (3.5 Tons)
Heating Load: 20,000 BTUs
Equipment Choice: You would install a large 3.5 or 4-ton Air Conditioner (or Heat Pump). The heating requirement is so small that the heat pump strip heat or a tiny gas furnace is more than enough.
Cold Climate Heating Load (Minneapolis)
In Minneapolis, the cooling season implies moderate humidity, but the winter is lethal.
The Load:
Cooling Load: 24,000 BTUs (2 Tons)
Heating Load: 80,000 BTUs!
Equipment Choice: You need a massive 80k BTU gas furnace (or hyper-heat cold climate heat pump). BUT, you only need a small 2-ton AC.
The Oversizing Trap
If a builder uses the "Phoenix Plans" in Minneapolis, they might accidentally put in a 3.5 Ton AC unit because the house size is the same. That unit would be massive overkill for Minneapolis summers, leading to terrible humidity control.
Humidity: The Silent Factor
What about Florida? Miami has a lower peak temperature (91°F) than Phoenix (108°F), but the Latent Load (humidity) is off the charts.
In humid climates, we often must prioritize humidity removal over temperature drop. This might mean sizing differently or requiring 2-stage equipment that can run long, slow cycles to "wring out" the air.
Where do you live?
Our calculator automatically pulls strict weather data for your specific zip code.
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