An auto changeover thermostat holds a comfort range by switching between heating and cooling on its own, using separate heat and cool setpoints.
Spring weather flips the house from chilly at 6 a.m. to stuffy by 3 p.m., and nobody wants to keep walking to the wall to pick a side. Auto changeover mode lets a thermostat run heat in the morning and air conditioning in the afternoon without anyone touching it. This article explains what the mode does, how the thermostat decides which system to run, the deadband rule that trips people up during setup, and the one outdoor temperature condition where Honeywell says to turn the feature off.
What Auto Changeover Actually Does
In Auto Changeover, the thermostat holds two setpoints at once — a heat target and a cool target — and can run either the furnace or the air conditioner as needed. Honeywell’s support documentation describes it as the mode that automatically switches between heating and cooling to hold a comfort range, instead of forcing you to choose one system for the day.
The thermostat watches indoor temperature and picks the system that pushes the reading back toward the range. Drop below the heat setpoint, and heat comes on. Climb above the cool setpoint, and cooling comes on. Between the two targets, nothing runs.
How It Decides: Heat, Cool, or Nothing
The decision comes down to where the indoor temperature sits relative to the two setpoints. Honeywell’s guidance explains that the thermostat automatically selects heating or cooling depending on indoor temperature, so the system in use changes with the weather rather than with your schedule.
This makes the most sense in climates where heating and air conditioning are needed on the same day — shoulder seasons, high-desert evenings, and coastal mornings. Without the mode, you either pick heat and roast by noon or pick cool and shiver until the house warms up.
A few practical details from Honeywell’s documentation:
- Set the system mode to AUTO first — the feature isn’t active in HEAT or COOL.
- Adjust targets with the + or – buttons, or the arrow keys, depending on the model.
- If the wrong target is flashing, switch the mode to edit the other setpoint, then return to Auto.
- The display may read Auto Heat or Auto Cool to show which system is currently running.
Some models keep the two setpoints from drifting too close together.
Deadband and Setpoint Rules
Some thermostats enforce a fixed deadband between the heat and cool setpoints so the equipment never short-cycles between the two systems.
Practically, that means you can’t set heat to 70°F and cool to 71°F. The thermostat will move the second setpoint to hold the gap. If your target temperatures seem to snap back after you enter them, the deadband is doing its job, not malfunctioning.
When Auto Changeover Is Unavailable or Unsafe
Two things can block or override the mode. Honeywell’s installation documentation notes that a setup function or installer setting can control whether the Auto option appears at all, so some thermostats only expose Auto Changeover after the installer enables it. The RTH6450 and RET95E documentation includes Auto Changeover directly, while other models may require configuration before the option shows up.
The other is outdoor temperature.
This matters most in fall and early spring, when an afternoon warm spell can trigger cooling while the outdoor unit is still sitting in freezing air. Below that threshold, manual mode is the safer call.
Auto Changeover is standard on many residential thermostats sold in the United States, from single-stage 1 heat/1 cool setups up to multi-stage systems, depending on the model family. If you’re replacing an older unit and want this mode out of the box, our tested roundup of the best auto changeover thermostats compares the models that support it — worth a look before you commit to a model that needs installer configuration first.
| Behavior | What It Means | Real-World Impact |
|---|---|---|
| Two setpoints | Heat target and cool target both held | No daily mode switching |
| Auto switching | Thermostat picks heat or cool | Handles same-day swings |
| Fixed deadband | 3-degree gap between setpoints | Targets snap back if set too close |
| Display states | Shows “Auto Heat” or “Auto Cool” | Tells you which system is running |
| Installer setting | Setup function can hide the Auto option | Some models need configuration first |
| 50°F limit | Use manual changeover below 50°F | Avoids possible compressor damage |
| Model support | RTH6450 and RET95E include it; others vary | Check the manual before buying |
Honeywell’s own overview of auto changeover mode covers the full feature explanation in more detail.
FAQs
Do I need two separate thermostats for auto changeover to work?
No. One thermostat holds both a heat and a cool setpoint and switches between the furnace and air conditioner automatically. You don’t need separate devices, but the thermostat itself has to support the mode. Some models only expose it after the installer enables the relevant setup function.
Why won’t my thermostat let me set heat and cool close together?
The unit is enforcing its deadband. In Honeywell model families that use a fixed 3-degree separation, the thermostat adjusts your setpoints automatically to preserve that gap. The snap-back isn’t a glitch — it’s the thermostat keeping the two systems from fighting each other or short-cycling the compressor.
Is auto changeover safe to leave on all winter?
Not if outdoor temperatures drop below 50°F (10°C). For most of the country, that means turning the feature off through the cold months.
References & Sources
- Honeywell Home. “Auto Changeover Mode On Your Thermostat.” Explains the mode, setpoint behavior, and the 50°F safety limit.
- Honeywell Home. “Auto Changeover Feature.” Covers how the thermostat selects heating or cooling in Auto mode.
- Resideo / Honeywell. RTH6350/RTH6450/RET93E/RET95E Series Technical Literature. Documents the fixed 3-degree separation and installer setup options.
