HVAC Sizing Calculator
Get a recommended tonnage based on your home's square footage.
Select the range that best matches your home's conditioned square footage, or enter an exact number below.
Or enter exact square footage
Roughly 500–600 sq ft per ton for our region.
We recommend — for —.
Choosing the right size HVAC system is one of the most important decisions you'll make when replacing or installing new equipment. An undersized unit won't keep up on hot days. An oversized unit will short-cycle, waste energy, and leave your home humid and uncomfortable. This guide walks you through everything you need to know.
Step 1: Know Your Climate Zone
The U.S. is divided into five climate zones for HVAC sizing. Hotter climates need more cooling capacity per square foot. Florida falls in Zone 1 (the hottest), which means systems work harder and sizing is especially important.
Our customers: Since Ace Air Direct is based in Florida (Zone 1), our calculator defaults to Zone 1 sizing. If you're in a different zone, the chart below shows adjusted ranges.
Step 2: Cooling — Tonnage by Square Footage
Use this chart to find the recommended AC tonnage for your home. Find your climate zone across the top, then match your square footage on the left.
| Tonnage | Zone 1 | Zone 2 | Zone 3 | Zone 4 | Zone 5 |
|---|---|---|---|---|---|
| 1.5 Ton | 600–900 sf | 600–950 sf | 600–1,000 sf | 700–1,050 sf | 700–1,100 sf |
| 2 Ton | 901–1,200 sf | 951–1,250 sf | 1,001–1,300 sf | 1,051–1,350 sf | 1,101–1,400 sf |
| 2.5 Ton | 1,201–1,500 sf | 1,251–1,550 sf | 1,301–1,600 sf | 1,351–1,600 sf | 1,401–1,650 sf |
| 3 Ton | 1,501–1,800 sf | 1,501–1,850 sf | 1,601–1,900 sf | 1,601–2,000 sf | 1,651–2,100 sf |
| 3.5 Ton | 1,801–2,100 sf | 1,851–2,150 sf | 1,901–2,200 sf | 2,001–2,250 sf | 2,101–2,300 sf |
| 4 Ton | 2,101–2,400 sf | 2,151–2,500 sf | 2,201–2,600 sf | 2,251–2,700 sf | 2,301–2,700 sf |
| 5 Ton | 2,401–3,000 sf | 2,501–3,100 sf | 2,601–3,200 sf | 2,751–3,300 sf | 2,701–3,300 sf |
1 ton of cooling = 12,000 BTU/hr. A 3-ton unit produces 36,000 BTU/hr of cooling capacity.
Don't Oversize Your System
Bigger is not better with HVAC. An oversized air conditioner will "short cycle" — turning on and off too frequently without running long enough to properly dehumidify your home. This is especially problematic in Florida's humid climate.
- Higher energy bills from constant cycling
- Poor humidity control — your home feels clammy even when cool
- Shorter equipment lifespan from wear on the compressor
- Uneven temperatures throughout the house
When in doubt between two sizes, the smaller unit is usually the better choice for our climate.
Already Have a System? Find Your Size
If you're replacing an existing system, the easiest approach is to match the size you already have. Manufacturers encode the capacity in the model number of your outdoor unit (the condenser or package unit). Look for one of these numbers in the model number — it tells you the BTU capacity in thousands:
For example, if your model number contains 36, you have a 3-ton system (36,000 BTU ÷ 12,000 = 3 tons). Look for the data plate on the side of your outdoor unit.
Heating: BTU Sizing Guide
Furnace and heating capacity is measured in BTU (British Thermal Units) rather than tonnage. The required BTU per square foot depends on your climate zone and how well your home is insulated. Use the lower number for well-insulated homes and the higher number for older homes with poor insulation.
| Zone 1 | Zone 2 | Zone 3 | Zone 4 | Zone 5 |
|---|---|---|---|---|
| 30–35 BTU/sf | 35–40 BTU/sf | 40–45 BTU/sf | 45–50 BTU/sf | 50–60 BTU/sf |
Example: Sizing a Gas Furnace
Say your home is in Zone 2 (Southeast), well-insulated, and 2,000 sq ft of heated space:
For a gas furnace, divide the required output by the furnace's efficiency rating to find the input BTU you need. An 80% AFUE furnace rated at 100,000 BTU input produces 80,000 BTU of actual heat output (100,000 × 0.80). A 96% AFUE furnace at the same input produces 96,000 BTU — more heat from the same fuel.
Variables That Affect Your Sizing
Square footage is a starting point, but several factors can push your needs up or down. Here's what to consider:
Insulation Quality
Well-insulated homes hold conditioned air better. Older homes with poor insulation may need to size up. Newer construction with modern insulation can often use the smaller end of the range.
Windows
More windows = more heat gain. Large, single-pane, or south/west-facing windows let in significantly more heat. Homes with many windows or older glass may need a larger system.
Ceiling Height
Standard sizing assumes 8-foot ceilings. Vaulted or 10+ foot ceilings increase the volume of air that needs conditioning. Add roughly 10–15% for every 2 feet above standard.
Number of Stories
In a two-story home, the second floor acts as insulation for the first. The upstairs typically runs warmer. Multi-story homes may benefit from zoned systems or separate units per floor.
Sun Exposure
Homes with heavy sun exposure on the roof and walls absorb more heat. Tree shade, light-colored roofing, and radiant barriers all reduce cooling load.
Ductwork Condition
Leaky or undersized ductwork can waste 20–30% of your system's output. If your ducts are in poor shape, even a perfectly sized unit will underperform. Have them inspected before upgrading.
Rule of thumb: If your home is well-insulated with newer windows, go with the smaller size in your range. If it's older with lots of glass and poor insulation, lean toward the larger size.
Commercial Sizing
Commercial spaces have different requirements than residential. Here's a quick method for estimating commercial cooling needs (assumes standard 8-foot ceilings):
- 1 Calculate the total square footage of the space to be cooled
- 2 Divide by 500, then multiply by 12,000 for base BTU
- 3 Add 380 BTU per person who regularly occupies the space
- 4 Add 1,000 BTU per window and 1,200 BTU per kitchen
- 5 Divide the total BTU by 12,000 to get the required tonnage
Example: 3,000 sq ft Office
Still Not Sure? We're Here to Help.
Our HVAC specialists can help you choose the right size system for your home. For the most accurate sizing, we recommend a professional Manual J load calculation — but for most standard homes, the chart above will get you in the right range.