How this calculator works
Your home needs a certain amount of cooling and heating each year, measured in BTU. The calculator multiplies your system size by the "full-load hours" for your climate, then divides by how efficiently each system turns energy into cooling or heat.
- Yearly cooling load (BTU) = tons × 12,000 × cooling hours
- Yearly heating load (BTU) = tons × 12,000 × heating hours
- Cooling kWh = cooling BTU ÷ (SEER2 × 1,000)
- Heat pump heating kWh = heating BTU ÷ (HSPF2 × 1,000), plus any share done by backup strips at 3,412 BTU per kWh
- Gas furnace therms = heating BTU ÷ (AFUE × 100,000)
- Electric resistance heat = heating BTU ÷ 3,412 per kWh
- Cost = kWh × your electric rate, therms × your gas rate
- Simple payback = (heat pump cost − incentives − cost of replacing AC + furnace) ÷ yearly savings. It ignores financing, rate increases and maintenance.
The tool assumes both the old and new system are the same size and that your home needs the same amount of cooling and heating either way. Better-sealed ducts or a different size could change that. The 15-year figure is yearly savings × 15 minus the extra cost, with no energy price increases.
SEER vs SEER2, HSPF vs HSPF2
Equipment made since January 2023 is rated with SEER2 and HSPF2, which use a tougher test. If your old unit shows SEER and HSPF, the calculator converts: SEER2 ≈ SEER × 0.95 and HSPF2 ≈ HSPF × 0.85. These are the RESNET conversion factors for ducted split systems (MINHERS Addendum 71f). The new heat pump is always entered in SEER2 and HSPF2, as on its label.
Where the climate numbers come from
Full-load hours vary a lot with house, thermostat habits, duct quality and how oversized the equipment is. Houston and Dallas use the equivalent full-load hours in the Texas Technical Reference Manual v13, Volume 2, Table 29 (central AC and heat pumps, based on the ENERGY STAR Central AC/HP savings calculator): Houston 2,209 cooling and 1,127 heating hours, Dallas 1,926 and 1,343. Treat the heating hours as generous, because they assume typical installed (often oversized) equipment. Austin / San Antonio is a midpoint of the Dallas and Houston values (an estimate; the TRM has no Austin zone). The other cities are rounded planning estimates that follow each city's degree-day pattern in NOAA's 1991–2020 climate normals, not measured or published values, so they are not directly comparable with the Texas rows. Overwrite the two hours fields with a better number if you have one, such as from an energy audit.
| Preset | Cooling hrs | Heating hrs |
|---|---|---|
| Houston (Texas TRM) | 2,209 | 1,127 |
| Dallas-Fort Worth (Texas TRM) | 1,926 | 1,343 |
| Austin / San Antonio (estimate) | 2,070 | 1,235 |
| Miami | 2,500 | 100 |
| Atlanta | 1,400 | 900 |
| Phoenix | 2,200 | 450 |
| Charlotte | 1,200 | 1,100 |
| Denver | 600 | 1,600 |
| Chicago | 700 | 1,900 |
| Seattle | 250 | 1,300 |
Energy price defaults
- Electricity, $0.16 per kWh: rounded from the EIA monthly average residential price for Texas in 2026 (about 15.9 to 17 cents). Source: EIA Electric Power Monthly, Table 5.6.A.
- Natural gas, $1.70 per therm: the EIA Texas residential gas price was about $16 to $19 per thousand cubic feet in early 2026 (EIA Texas natural gas prices). One thousand cubic feet is about 10.4 therms, so that is roughly $1.55 to $1.85 per therm. Summer prices per unit look much higher because fixed monthly charges are spread over very little gas, so the winter number is the better one for heating.
Install cost defaults
The $11,000 (AC plus gas furnace) and $10,500 (ducted heat pump) defaults sit inside the published 2026 ranges for a typical 2.5 to 3 ton replacement on existing ductwork, roughly $5,500 to $13,000 for a furnace and AC and $6,000 to $14,000 for a ducted heat pump. See Angi, HVAC replacement cost and HVACBase, heat pump installation cost. They are placeholders, not quotes.
Is there a federal tax credit?
As of October 2026, no. The 25C Energy Efficient Home Improvement Credit, which covered 30% of heat pump costs up to $2,000 a year, was ended by the One Big Beautiful Bill Act (Public Law 119-21) for property placed in service after December 31, 2025. A heat pump that was installed and working by that date still qualifies on a 2025 tax return. See the IRS FAQs on changes to 25C and other credits. Some electric utilities and states may still offer their own rebates, which are separate. Ask your electric company and contractor, and enter any rebate in the incentives box.
Hot-humid Gulf Coast notes
- Humidity: in cooling mode a heat pump dehumidifies like any air conditioner. Size matters. An oversized unit short-cycles and leaves the house clammy. Ask for a Manual J load calculation.
- Backup heat: a few nights a year drop near freezing. Most Houston heat pumps include electric backup strips. The backup box above lets you test how that changes the result.
- Ducts: leaky attic ducts waste more energy than the gap between two efficiency ratings. Ask about duct sealing and testing.
- Gas is cheap, electricity less so: where gas is inexpensive, a gas furnace can still be cheaper to run on the coldest days. The heat pump usually wins on cooling efficiency.
- More background: U.S. Department of Energy, Heat Pump Systems.
This is a planning estimate, not a quote or an energy audit. Actual bills depend on your house, ducts, thermostat habits and weather.