Converting to a Heat Pump: What Changes and What Does Not
Switching from an air conditioner plus gas furnace to a heat pump is straightforward in Phoenix. Here is what the conversion actually involves.
Converting to a heat pump in Phoenix involves replacing the outdoor unit with a heat pump, replacing or modifying the indoor unit, updating thermostat wiring for reversing valve and auxiliary heat control, and verifying electrical capacity for backup heat strips. In the mild Valley climate the performance result is generally excellent.
Why the conversion is easy here
A heat pump is mechanically an air conditioner with a reversing valve. The outdoor unit looks the same, occupies the same pad, uses the same line set in most cases, and cools identically.
The Phoenix climate is close to ideal for one. Winters are mild enough that a heat pump operates in its efficient range nearly the whole heating season, which means you get the efficiency benefit without the backup-heat penalty that makes conversions questionable in colder states.
For a home with no gas service, or with an aging furnace that is due anyway, a heat pump replaces two pieces of equipment with one.
What the conversion involves
- New outdoor unit. A heat pump condenser rather than a cooling-only condenser.
- Indoor unit. Either an air handler with electric backup heat strips, or the existing furnace retained in a dual-fuel configuration.
- Thermostat. Heat pump control requires reversing valve control (O or B) and auxiliary heat control (W2 or AUX), which older thermostat wiring may not support.
- Electrical. Backup heat strips draw substantial current. Panel capacity and circuit sizing need evaluation, not assumption.
- Configuration. Equipment type, staging, reversing valve orientation, and auxiliary heat lockout all set correctly.
The three configurations
| Setup | Backup heat | Best for |
|---|---|---|
| Heat pump + air handler with strips | Electric resistance | Homes without gas service; the common conversion |
| Dual fuel (heat pump + existing furnace) | Gas furnace | Homes with a working furnace worth keeping |
| Heat pump only, no backup | None | Rare here; risky on the coldest mornings |
Dual fuel deserves specific mention for Valley homes replacing an air conditioner while the furnace is still in good condition. You get heat pump economics for nearly the whole season without discarding working equipment, and the furnace covers the handful of genuinely cold mornings.
The electrical question
This is the item that surprises people on a quote. Electric backup heat strips draw considerably more current than a cooling-only system does — often enough to require a dedicated circuit, a larger breaker, and sometimes a panel evaluation.
Older Valley homes were built with smaller electrical services than modern loads assume, and a home that has also added an EV charger or a mini split may be closer to capacity than the owner realizes.
A load calculation on the electrical service is part of doing the job properly. A contractor who does not mention electrical on a heat pump conversion is skipping a step.
What you will notice
Supply air feels cooler in heating. A heat pump delivers air around 90 to 100 degrees; a furnace delivers 120 or more. The house reaches the same temperature, but the air from the register does not feel hot. This is the single most common adjustment for people new to heat pumps and it is entirely normal.
Longer heating cycles. A heat pump runs longer at lower output rather than in short intense bursts. That produces more even temperatures.
The defrost cycle. On cold mornings the unit will periodically reverse briefly to melt frost off the outdoor coil, producing visible steam and a few minutes of cool air. Normal.
Different bill pattern. Heating moves from the gas bill to the electric bill, which makes a year-over-year comparison confusing unless you look at both.
The configuration mistakes to avoid
Nearly every heat pump problem we find on a converted system is configuration rather than equipment.
Auxiliary heat lockout never set, so strips run on mild mornings. Thermostat set to conventional rather than heat pump, so the reversing valve logic is wrong. Reversing valve orientation set to the wrong terminal. Deep thermostat setbacks scheduled as if the system were a furnace, which triggers strip heat during every recovery.
Each of those is invisible in terms of comfort and expensive on the bill. Ask specifically what the auxiliary lockout is set to, and verify it at the first fall maintenance visit.
Frequently asked
Can I convert from a gas furnace to a heat pump?
Yes, and Phoenix is close to an ideal climate for it. The conversion involves a heat pump outdoor unit, an air handler with electric backup or a dual-fuel setup retaining the furnace, updated thermostat wiring, and an electrical evaluation for backup heat strips.
Does a heat pump feel different than a furnace?
Yes. Supply air runs around 90 to 100°F rather than 120 or more, so it does not feel hot at the register even though the house reaches the same temperature. Cycles are longer and gentler, which produces more even temperatures.
Do I need an electrical upgrade for a heat pump?
Possibly. Electric backup heat strips draw considerably more current than a cooling-only system, and older Valley homes were built with smaller services. A dual-fuel configuration that retains a working gas furnace avoids the question entirely.