how to choose a unit

Easy-to-Use A/C Size Selection Tool
Use this guide to help determine the correct air conditioner size for your home.

Refer to the color-coded map above to identify the climate zone your home is located in.
Using the chart below, match your home’s square footage with your climate zone.
Select the A/C unit size (tonnage) that corresponds to your square footage and zone for optimal efficiency.

Proper System Sizing
Selecting the correct A/C size involves precise calculations. One industry-standard method is a Residential Load Calculation, which accounts for insulation, windows, layout, and climate.

Another reliable approach is identifying the size of your existing system. While manufacturers may not list tonnage directly, the capacity is almost always encoded in the model number of the outdoor unit.

Model Number Tonnage Reference
18 = 1.5 tons
24 = 2 tons
30 = 2.5 tons
36 = 3 tons
42 = 3.5 tons
48 = 4 tons
60 = 5 tons
 
Important Sizing Warning
Avoid purchasing an oversized air conditioner. Systems that are too large will short cycle, meaning they shut off before adequately removing humidity. Short cycling leads to:

Poor humidity control
Higher energy costs
Increased wear and reduced system lifespan
Proper sizing is essential for comfort, efficiency, and durability.

 
Heating Square Footage by Climate Zone
Zone
Heating Requirement
Zone 1
30–35 BTUs per sq. ft.
Zone 2
35–40 BTUs per sq. ft.
Zone 3
40–45 BTUs per sq. ft.
Zone 4
45–50 BTUs per sq. ft.
Zone 5
50–60 BTUs per sq. ft.
 
Heating Guide
Use the lower value if your home is well insulated.
Use the higher value if your home is older or poorly insulated.
If you are unsure, select the higher value.
Example Heating Calculation
Home size: 2,000 sq. ft.
Climate zone factor: 40 BTUs
2,000 × 40 = 80,000 BTUs required (output)

Furnace Output Calculation
To determine furnace output:

Multiply the furnace’s input rating by its efficiency.
Example:

100,000 BTU input × 80% efficiency = 80,000 BTU output
100,000 BTU input × 93% efficiency = 93,000 BTU output
In the example above, a 2,000 sq. ft. home requiring 80,000 BTUs would need a 100,000 BTU input furnace at 80% efficiency.