Repair Costs
HVAC Repair vs Replace: The Complete 2025 Guide
When it's time for a new unit - and what size to buy.
How AC Sizing Works
The correct approach to AC sizing is Manual J - the ACCA-approved load calculation standard. Our calculator uses the key Manual J variables to give you a reliable estimate. For exact sizing before purchase, always request a full Manual J from your HVAC contractor.
Why Proper Sizing Matters
| Issue | Oversized Unit | Undersized Unit |
|---|---|---|
| Runtime pattern | Short cycles (2-3 min on/off) | Runs constantly |
| Humidity control | Poor - feels clammy | Ok but can't keep up |
| Energy use | High - frequent start/stop | High - constant run |
| Equipment life | Shorter - stress from cycling | Shorter - constant load |
| Mold risk | High - poor dehumidification | Low |
Quick Reference: Size by Square Footage and Climate
| Home Size | Hot Climate | Moderate | Cold Climate |
|---|---|---|---|
| 1,000 sq ft | 2 - 2.5 tons | 1.5 - 2 tons | 1 - 1.5 tons |
| 1,500 sq ft | 2.5 - 3 tons | 2 - 2.5 tons | 1.5 - 2 tons |
| 2,000 sq ft | 3 - 3.5 tons | 2.5 - 3 tons | 2 - 2.5 tons |
| 2,500 sq ft | 3.5 - 4 tons | 3 - 3.5 tons | 2.5 - 3 tons |
| 3,000 sq ft | 4 - 5 tons | 3.5 - 4.5 tons | 3 - 4 tons |
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Frequently Asked Questions
The old rule of thumb is 1 ton per 400-600 sq ft, but this is oversimplified. The actual calculation depends on climate, ceiling height, insulation, and windows. In hot climates, plan for 1 ton per 350-400 sq ft. In moderate climates, 1 ton per 500-600 sq ft. Always use the full Manual J calculation or this calculator for accurate sizing.
Neither - proper sizing is critical. An oversized unit short-cycles (turns on/off too frequently), wastes energy, and fails to dehumidify properly, leading to a clammy feeling and mold risk. An undersized unit runs continuously without reaching target temperature. Studies show 50% of installed systems are improperly sized.
Manual J is the ACCA-approved industry standard for residential heating and cooling load calculations. It accounts for climate, square footage, ceiling height, insulation levels, window count/size/orientation, home age, occupancy, and internal heat sources. Our calculator uses a simplified version - for a full Manual J, hire a certified HVAC technician.
Hot-humid climates (Houston, Miami, Atlanta) need 25% more capacity than the baseline calculation. Hot-dry climates (Phoenix, Las Vegas) need 20% more. Moderate climates (San Francisco, Seattle) match the baseline. Cold climates (Minneapolis, Denver) can use 15% less cooling capacity since summers are shorter.
Yes. Standard sizing assumes 8-foot ceilings. For 9-foot ceilings, add about 12.5% more capacity. For 10-foot ceilings, add 25%. Vaulted ceilings with exposed south-facing roof add even more load. Our calculator accounts for this automatically.
Any time you replace your HVAC system, add significant square footage, or make major changes to insulation or windows. The cost is $200-$400 and protects you against a $5,000+ sizing mistake. Always request Manual J calculations from contractors before approving a new unit installation.