TryBuildCalcAC Replacement Savings Calculator (Old AC vs. New AC, Normalized SEER2 Basis)
Estimate your AC replacement savings instantly.
🕒 Last updated: September 18, 2026
Inputs
ℹ️Same capacity assumed for both the old and new unit — this isolates the efficiency difference as the only variable.
ℹ️Prefills a typical annual cooling hours estimate below — edit that field directly if you know your actual usage.
ℹ️A smart thermostat's own runtime log (if available) is more accurate than this climate-zone default.
ℹ️Use your summer/peak-season rate if your utility has time-of-use pricing, for the most realistic cooling-season estimate.
Current (Old) System
ℹ️Most units installed before 2023 carry a SEER rating, not SEER2.
ℹ️From the nameplate or an AHRI Directory lookup by model number, not guessed from the unit's age.
New / Replacement System
ℹ️Virtually every unit sold since 2023 carries a SEER2 rating.
ℹ️From the specific quoted model's spec sheet, for the exact indoor/outdoor combination being installed.
ℹ️Enter your NET cost after any rebates/tax credits to unlock a simple payback period below.
Estimated Annual Savings
$403
37.2% less cooling energy use per year
Current (Old) System
Entered rating: 10 SEER
SEER2-equivalent: 9.6
Annual energy use: 6,785 kWh
Annual cost: $1,086
New / Replacement System
Entered rating: 15.2 SEER2
SEER2-equivalent: 15.2
Annual energy use: 4,263 kWh
Annual cost: $682
Cumulative Savings Over Time
Year 1
$403
Year 5
$2,015
Year 10
$4,030
Year 15
$6,045
Year 20
$8,060
Assumptions Used
Annual kWh = (Tonnage × 12,000 BTU/ton ÷ SEER2-equivalent rating) × Annual Cooling Hours ÷ 1000, computed once for each unit and multiplied by your electricity rate. A rating entered as SEER (pre-2023) is normalized to an approximate SEER2-equivalent by dividing by 1.047 before this formula runs — DOE's 2023 M1 test procedure reads roughly 4.5-5% lower than the old SEER test for identical equipment, though the real difference varies by equipment type (variable-speed ~3-4%, single-speed ~5-6%), so this is a published approximation, not an exact per-unit conversion. Annual cooling hours default from your selected climate zone as a broad planning estimate — no single authoritative national table exists, so your own smart-thermostat runtime log (if available) is more accurate than this default. The payback period (when shown) is simply net installed cost ÷ annual savings, and the cumulative savings table assumes a flat electricity rate with no future inflation, financing costs, or maintenance-cost differences between the two units — this is a planning estimate, not a full financial analysis.
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete SEER Savings Calculator.
AC replacement savings sizing
Replacing a very old 10 SEER central air conditioner (common in units installed before the early 2000s) with a modern 15.2 SEER2 unit is one of the largest realistic efficiency jumps available, since older units predate today's minimum efficiency standards by a wide margin.
This page defaults to a 3-ton system in a mixed climate zone — edit the inputs above to match your actual system and location.
SEER Savings Formula: How Is It Determined?
The same formula runs once for each unit, using each unit's normalized SEER2-equivalent rating, then the two results are compared.
SEER-to-SEER2 Normalization
If rating type is SEER2: SEER2-equivalent = entered value (no change)
If rating type is SEER: SEER2-equivalent = entered value ÷ 1.047
DOE's 2023 M1 test procedure for SEER2 uses much higher external static pressure than the old SEER test, so identical equipment reads a lower SEER2 number. 1.047is a commonly-cited approximate conversion factor — the real difference varies by equipment type (variable-speed/ECM systems see a smaller ~3-4% drop, single-speed/PSC systems a larger ~5-6% drop), so treat this as a planning approximation, not an exact per-unit figure. If you have a unit's actual AHRI-certified SEER2 rating, use that directly instead.
Annual Energy Use and Cost
Annual kWh = (Tonnage × 12,000 BTU/ton ÷ SEER2-equivalent) × Annual Cooling Hours ÷ 1000
Annual Cost = Annual kWh × Electricity Rate
This runs once using the old unit's normalized SEER2-equivalent and once using the new unit's — both assuming the SAME tonnage and cooling hours, so the only variable being measured is the efficiency-rating difference.
Annual Savings and Percent Reduction
Annual Savings = Old Unit Annual Cost − New Unit Annual Cost
Percent Energy Reduction = (Old Annual kWh − New Annual kWh) ÷ Old Annual kWh × 100
A negative annual savings figure means the "new" unit is actually less efficient than the "old" one once both are normalized — this calculator reports that honestly rather than hiding it.
Payback Period (Optional) and Cumulative Savings
Simple Payback Period = New System Installed Cost ÷ Annual Savings
Cumulative Savings (Year N) = Annual Savings × N
Payback period only appears when an installed cost is entered and savings are positive (and the payback period is under 100 years). The cumulative savings table assumes a flat electricity rate over time, with no adjustment for future rate inflation, financing costs, or maintenance-cost differences between the two units.
Worked Example
This example walks through your current inputs above, using the same steps as the Formula section.
Input Values Used
| Input | Value |
|---|---|
| Cooling capacity / climate zone | 3 tons / Zone 4 — Mixed (Mid-Atlantic, TN, OK, N. CA) |
| Annual cooling hours / rate | 1800 hrs / $0.16/kWh |
| Old unit rating | 10 SEER (pre-2023 rating) |
| New unit rating | 15.2 SEER2 (2023+ DOE rating) |
Step-by-Step Calculation
| Step | Calculation | Result |
|---|---|---|
| Old unit SEER2-equivalent | 10 ÷ 1.047 | 9.6 |
| New unit SEER2-equivalent | 15.2 (already SEER2) | 15.2 |
| Old unit annual kWh | (3 × 12,000 ÷ 9.6) × 1800 ÷ 1000 | 6,785 kWh |
| New unit annual kWh | (3 × 12,000 ÷ 15.2) × 1800 ÷ 1000 | 4,263 kWh |
| Old / New annual cost | kWh × $0.16 | $1,086 / $682 |
| Annual savings | $1,086 − $682 | $403 |
Therefore, replacing this 3-ton system rated 10 SEER (pre-2023 rating) with a new one rated 15.2 SEER2 (2023+ DOE rating) saves an estimated $403 per year (37.2% less cooling energy).
Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.