Heat pump vs furnace: which thermostat settings differ
A heat pump thermostat has settings a furnace thermostat never needs: the O or B changeover signal, compressor protection in winter, backup heat rules such as auxiliary heat (AUX) lockouts, and an emergency heat mode. A furnace setup instead uses furnace stage rules and minimum heat run times. The mode, schedule and fan basics are the same.
What stays the same on both systems?
The everyday controls. Heat, Cool, Auto and Off modes, the schedule, holds, and the fan choices of Auto, On or Circulate work the same way whether a heat pump or a furnace makes the heat. On a Honeywell Home T6 Pro Programmable, for example, the user manual describes the same mode and fan buttons for every system. The temperature differential also works the same way: it decides how far the room drifts before heat starts, whatever the equipment.
The differences sit one level down, in setup and equipment settings, and they all come from one fact. A heat pump makes heat with a compressor and switches between heating and cooling, and it usually has a second, more expensive heat source as backup. A furnace is a single heat source that only heats.
Which settings differ?
| Setting | Heat pump | Furnace |
|---|---|---|
| System type | Heat Pump (Honeywell T6 Pro option 200 = 2) | Conventional Forced Air Heat (option 200 = 1, the factory value) |
| O or B changeover signal | Required; T6 Pro option 218, O from the factory | Not used |
| Compressor protection | Applies in heating as well as cooling | Applies only to the air conditioner, in cooling |
| Backup heat rules | Lockout temperature for auxiliary heat (AUX), droop, upstage timer, compressor lockout | Not used |
| Emergency heat mode | Available when backup heat is configured | Not offered |
| Second stage rules | Compressor stage 2, then AUX | Furnace stage 2 |
| Minimum run time (Nest) | "Minimum Compressor On Time", 5 minutes by default | "Minimum Heat On Time", 3 minutes by default |
| Comfort versus cost feature (Nest) | Heat Pump Balance | Early-On |
Why does a heat pump need a changeover setting?
A heat pump runs the same equipment in two directions, and a valve inside it decides which. The thermostat sends a signal to that valve, and it has to know whether the equipment expects the signal for cooling (O) or for heating (B). Honeywell's T6 Pro asks this in option 218. Google's Nest guide adds a second choice: whether to send the signal on each cycle or keep it on for the whole season. A furnace has no such valve, so its thermostat never asks. When this setting is wrong, heating and cooling come out reversed, which is covered in heat pump blowing cool air while the thermostat says heat and in the system type setting.
What extra settings come with backup heat?
This is the biggest group. A heat pump thermostat has to decide when to add AUX, and every brand gives installers several ways to tune it:
- Outdoor lockouts. The Honeywell Home T6 Pro has "Outdoor Lockout Backup Heat" (option 356) and "Compressor Lockout / Balance Point" (option 355); both are off from the factory. ecobee has "Compressor Min Outdoor Temperature" and an AUX outdoor ceiling, explained in ecobee's AUX outdoor temperature setting. Google's Nest guide gives an AUX lockout default of 40°F.
- Time and temperature rules. The T6 Pro's "Backup Heat Droop" (option 340) and "Upstage Timer for Backup Heat" (option 350); ecobee's "Compressor to Aux Temperature Delta" or "Compressor to Aux Runtime"; Nest's droop, Aux Upstage Timer and Minimum Delay.
- A preference instead of numbers. Nest's Heat Pump Balance and ecobee's "Aux Savings Optimization" let you pick comfort, savings or a balance.
A furnace thermostat has none of this. If a furnace system has two stages, the only staging choice is when to bring on the second stage, and ecobee keeps that separate as "Heat Stage 2 Temperature Delta" or "Heat Stage 1 Max Runtime". Stage 1 vs stage 2 heat explains both kinds.
Do schedules and setbacks behave differently?
They work the same, but they cost differently. On a furnace, a big overnight setback and a quick morning warm-up simply mean the furnace runs longer. On a heat pump, a big jump in setpoint is one of the classic reasons the thermostat calls on AUX, which costs far more than the heat pump; why a thermostat shows AUX covers this in detail. Thermostats try to soften it with recovery mode, which starts heating earlier so the house reaches the setpoint on time.
The air also feels different. Trane puts heat pump air at roughly 85 to 93°F, and Carrier says a fuel-burning furnace delivers roughly 120 to 140°F. That is normal and does not call for a different setting.
What about timing and protection settings?
Compressor protection is the one people notice. On a heat pump, the thermostat holds the compressor off for a few minutes after it stops, in winter as well as summer. Honeywell's T6 Pro manual says "Heat On" flashes during that wait if you have a heat pump.
Cycle rates differ too. Honeywell's T6 Pro keeps separate options for compressor stages and heating stages, and its recommended cycles per hour (CPH) depend on the heating equipment type chosen in setup.
Finally, emergency heat (EM heat) exists only on heat pump systems with backup heat. Honeywell says the T9 offers "Em Heat" only when configured for a heat pump with an auxiliary or emergency heat stage. If you have a furnace and see that mode, the thermostat setup does not match the equipment. If you have a heat pump and the mode is on by accident, see why a thermostat says emergency heat.
Frequently asked questions
- Can I use the same thermostat for a heat pump and a furnace?
- Many thermostats support both, but each must be set up for the equipment it controls. On a Honeywell Home T6 Pro the installer picks Conventional Forced Air Heat or Heat Pump in installer option 200. The choice changes which settings appear afterward.
- Should I use a deep night setback with a heat pump?
- Be careful with it. Google notes that a heat pump system can use AUX heat to change the temperature quickly, and AUX costs more to run than the heat pump. A large morning jump in setpoint invites exactly that, so a smaller setback is the safer choice with a heat pump.
- Does a furnace have compressor protection?
- No. Compressor protection is a minimum off time for a compressor, which a furnace does not have. It applies to an air conditioner in summer and to a heat pump in both seasons.
- Why does my heat pump feel less warm than a furnace?
- Because its air is cooler. Trane puts heat pump air at about 85 to 93°F, and Carrier contrasts roughly 85 to 100°F from a heat pump with roughly 120 to 140°F from a fuel-burning furnace. The house still reaches the setpoint; the air just feels milder.