Heat Pump or Furnace? What Your Climate Zone Says
Published 2026-09-11Every metro page in our HVAC index names its IECC climate zone, because the zone answers the first question in a replacement conversation: should the new system be a heat pump, a furnace paired with an air conditioner, or both? The zone is not a recommendation by itself, but it sets the physics.
What a heat pump actually is
A heat pump is a central air conditioner with a reversing valve. In summer it moves heat out of the house; in winter it moves heat in from outdoor air, even cold air. Because it moves heat rather than making it, a heat pump delivers two to four units of heat per unit of electricity at mild temperatures. A gas furnace makes heat by burning fuel, at 80 to 98 percent efficiency, and does not care how cold it is outside.
The catch is that a heat pump's output and efficiency fall as the outdoor temperature falls. Standard units lose meaningful capacity below roughly 25 to 30°F; cold-climate models (variable-speed compressors rated to well below zero) hold capacity much lower, at a higher price. Below the balance point, where the pump cannot keep up, backup heat runs: electric resistance strips (cheap to install, expensive to run) or a gas furnace in a dual-fuel setup.
By climate zone
Zones 2A and 2B — Houston, San Antonio, Corpus Christi, Tucson, Mesa. Cooling dominates and winter lows rarely hold below freezing for long. A heat pump is the default: the cost over an AC-only unit is small, it replaces the furnace entirely, and backup strips run a handful of hours a year. Gas furnace plus AC still makes sense where gas is already piped and cheap, but the heat pump usually wins on total cost. Local figures: Houston, Mesa.
Zones 3A and 3B — Dallas, Oklahoma City, Memphis, Charlotte, Birmingham, El Paso, Lubbock. Both seasons carry a real load. A standard heat pump handles most winters; a few cold snaps a year hit the strips. This is where the electricity-versus-gas price comparison decides it, and where dual-fuel (a heat pump with a gas furnace as backup) is often the best answer in homes that already have gas. See Dallas and Oklahoma City.
Zones 4A and 4B — Nashville, Knoxville, Raleigh, Kansas City, Wichita, Amarillo. Heating hours rival cooling hours. A standard heat pump alone leans on backup heat through January; a cold-climate model or dual-fuel is the honest spec, and the heat pump row in our tables sits toward its upper half here for that reason. Compare Nashville and Kansas City.
Zone 5B — Denver, Colorado Springs. The furnace is the primary system. A heat pump works, but only a cold-climate unit sized for design-day lows or a dual-fuel pairing, and the installed cost reflects it. One local wrinkle: gas furnaces lose capacity with altitude and must be derated (roughly four percent per 1,000 feet above 2,000 feet), so a Denver furnace is sized and set up differently from the same model in Kansas. See Denver.
The fuel math
Operating cost comes down to two utility rates and one efficiency number. Cost to deliver 100,000 BTU of heat:
- Gas furnace: price per therm divided by AFUE. At $1.20 per therm and 95% AFUE, about $1.26.
- Heat pump: 29.3 kWh times price per kWh, divided by COP. At $0.14 per kWh and a COP of 3 (a mild day), about $1.37; at a COP of 2 (a cold day), about $2.05; on resistance backup (COP of 1), about $4.10.
Those are example rates, not yours. Put your own bill rates in and the crossover temperature falls out: above it the heat pump is cheaper to run, below it gas is. In the South the pump wins nearly all winter; in zone 5B the furnace wins most of it.
Installed cost and incentives
Our tables show heat pump installation running above a like-for-like AC replacement and below "AC plus new furnace" in most metros, with a wide spread because cold-climate equipment costs substantially more than standard units. The federal 25C tax credit that covered qualifying heat pumps ended for equipment placed in service after 2025 under the July 2025 tax law; utility and state rebates still exist in many areas and change often, so verify what applies to your install date before counting on any of it, and get it in writing on the quote.
Questions that settle it
- What is the design-day low for this address, and what is the proposed unit's capacity at that temperature (not its nameplate tonnage)?
- What is the backup: strips, gas, or none? What does the backup cost to run per hour?
- Is this a cold-climate model, and what is its rated capacity at 5°F?
- Was the sizing from a Manual J load calculation?
A heat pump is the right answer for most of the metros we cover. The zone tells you how much backup to buy with it.