Heat Pump vs. Gas Furnace: What Actually Changes the Answer?

The mistake: comparing equipment labels instead of the whole decision

A heat pump is both a heater and an air conditioner. A gas furnace is a heater. If one quote includes a complete heat-pump system and the other includes only a furnace while your air conditioner also needs replacement, the sticker prices are not comparable.

Start by making the scopes equivalent. If the furnace path requires a new central air conditioner, coil, electrical work, venting, or other mandatory work, include it. Do the same for the heat-pump path.

What the calculator actually compares

The model uses your current gas-furnace fuel use to estimate the amount of useful heat your home needs in a typical year. Then it asks how much purchased energy a new furnace or a heat pump would need to deliver that same amount of heat.

EIA defines one therm as 100,000 Btu, and one kilowatt-hour of electricity as 3,412 Btu. DOE defines AFUE as the ratio of annual useful heat output to fuel input. Those conversions let both systems be compared against the same delivered heating load.

Why the heat-pump COP matters so much

A heat pump moves heat rather than creating it directly from resistance heat. ENERGY STAR says an air-source heat pump can deliver up to about three times as much heat energy as the electrical energy it consumes under favorable conditions. But the number that matters for your bill is not a marketing peak—it is a realistic seasonal COP for your climate, equipment, controls, ductwork, and backup-heat strategy.

Cold-weather performance has improved substantially. ENERGY STAR's current cold-climate criteria require qualifying ducted split systems to meet HSPF2 requirements and demonstrate a COP of at least 1.75 at 5°F, while retaining at least 70% of their 47°F heating capacity at 5°F. That does not mean every heat pump performs the same way in every house.

Utility prices can flip the result

A high-efficiency gas furnace can turn a large share of each therm into useful heat. A heat pump can multiply each purchased kWh into multiple kWh of useful heat. Which one costs less to operate depends on the price of those two fuels and the actual seasonal efficiency of both systems.

That is why a national “heat pumps are always cheaper” or “gas is always cheaper” rule is weak. Two neighboring utilities can produce different economics with the same equipment.

A simple worked example

Suppose a home currently uses 700 therms per year for space heating with an 80% AFUE furnace. Compare a 95% AFUE replacement furnace with a heat pump using a seasonal COP of 2.8. Assume electricity costs $0.16/kWh and gas costs $1.50/therm.

In that example, gas wins on cost because its upfront quote is much lower and annual heating energy is slightly cheaper. But change the electricity rate, gas rate, heat-pump efficiency, incentives, or add a needed air-conditioner replacement to the furnace path and the result can move quickly.

The air-conditioner question can be decisive

If your furnace failed but your air conditioner is relatively new, replacing only the furnace can be a very different decision from replacing an aging furnace and aging air conditioner together. A heat pump already provides cooling, so a fair comparison should credit the furnace path with any AC work that is truly required.

ENERGY STAR specifically notes that when a home has a relatively new furnace and an older central AC, replacing the AC with a heat pump can create a dual-fuel system. That preserves the furnace as backup while adding heat-pump heating and new cooling.

Cold climate does not automatically rule out a heat pump

Modern cold-climate systems can provide meaningful heating output at low outdoor temperatures. Still, equipment selection and sizing matter. ENERGY STAR recommends having a contractor perform a Manual J heating and cooling load calculation and choosing equipment appropriate for the climate.

A cold-climate heat pump may be designed to carry the house without a furnace, or the home may use electric resistance or a gas furnace as backup. Backup strategy changes both comfort and operating cost, so it should be part of the quote—not an afterthought.

Do not count an expired federal credit

For 2026 installations, the federal Energy Efficient Home Improvement Credit under Section 25C is no longer available. The IRS says the credit is not allowed for property placed in service after December 31, 2025. State, local, utility, and manufacturer incentives may still exist, so enter only incentives you have verified.

What the calculator intentionally does not pretend to know

It does not forecast future utility inflation, assign a dollar value to emissions, model every hour of outdoor temperature, predict repair failures, or estimate home resale value. Those inputs can matter, but adding uncertain assumptions can make a calculator look more precise while making it less trustworthy.

The purpose is to expose the variables that can actually flip the decision and give you a checkable baseline.

A better decision process

Get comparable written quotes. Pull twelve months of utility usage. Separate space-heating gas from water-heating and cooking if possible. Ask for the exact furnace AFUE and heat-pump model. Ask how the contractor sized the system, what happens at low temperatures, and what backup heat is included.

Then change the calculator inputs. If the answer flips with a small change in utility rate or COP, you have a close call. If one option remains cheaper across a wide range of reasonable assumptions, the cost conclusion is more robust.