A dual fuel thermostat runs a heat pump and a gas, propane or oil furnace as one system. The heat pump heats your home in mild weather, and when it gets cold outside, the thermostat switches to the furnace. Getting that switch right is the whole job, and not every smart thermostat can do it.
The short answer: ecobee, Google Nest and Sensi thermostats support dual fuel, with different limits. The Nest Learning Thermostat (4th gen) handles every dual fuel setup in Google’s compatibility table, while the cheaper Nest Thermostat only handles single-stage systems. Honeywell Home’s current X series and the Amazon Smart Thermostat support electric backup heat only, so they won’t work with a dual fuel system. This guide explains how dual fuel works, how each brand decides when to switch, and which thermostat fits your system.
Dual Fuel Thermostats at a Glance
| At a glance | |
|---|---|
| What dual fuel means | A heat pump with a furnace (gas, propane or oil) as backup heat |
| What the thermostat does | Runs the heat pump in mild weather and switches to the furnace when it’s cold outside |
| How it decides | By outdoor temperature, using a switchover point you set (Nest, ecobee) or its own logic (Sensi) |
| Smart thermostats that support it | ecobee Premium, Enhanced and Essential; Nest Learning Thermostat; Nest Thermostat (single-stage only); Sensi Touch 2 and Sensi |
| Ones that don’t | Honeywell Home X8S, X7S and X7B; Amazon Smart Thermostat |
| Installation | Google recommends a professional for dual fuel systems |
What Is a Dual Fuel System?
A dual fuel system pairs an outdoor heat pump with an indoor furnace that burns natural gas, propane or oil. Both share the same ducts and blower. The heat pump does all the cooling in summer and most of the heating in spring and fall. When the outdoor temperature drops, the heat pump loses both efficiency and heating capacity, so the furnace takes over.
The key difference from a regular heat pump is the backup. Most heat pumps use electric heat strips in the indoor air handler as auxiliary heat, and those strips run together with the heat pump. A dual fuel furnace works the other way: when the furnace runs, the heat pump turns off. Google’s setup guide for Nest says dual fuel heat “will never run when heat pump heat is running.” That’s why a thermostat needs a specific dual fuel setting, and why one that only knows electric backup can’t run the system correctly.
You probably have a dual fuel system if:
- Your outdoor unit runs in winter. An air conditioner only runs in summer. A heat pump heats too.
- Your indoor unit is a furnace with a gas line, a flue pipe and a burner, not just an air handler with heat strips.
- Your current thermostat has an O or B wire. That’s the reversing valve wire every heat pump uses. Our thermostat wiring guide shows what each letter means.
- On a Nest thermostat, both W1 and W2 have wires. Google says that’s how you can tell a Nest is set up for dual fuel.
If your backup heat is electric, you don’t have dual fuel, and any thermostat that supports heat pumps with aux heat will do.
How a Dual Fuel Thermostat Decides When to Switch
Every thermostat on a dual fuel system answers one question: at what outdoor temperature should the furnace take over? That temperature is called the balance point, switchover point or breakpoint. Above it, the heat pump heats the house. Below it, the furnace does.
The U.S. Department of Energy’s building science training puts the switchover between 5°F and 35°F, depending on what your heat pump can do. A newer cold-climate heat pump can keep working at much lower temperatures than an older one. Your energy prices matter too: if electricity is expensive and natural gas is cheap where you live, a higher switchover point can cost less to run, and the opposite is also true.
Nest checks the outdoor temperature from local weather over Wi-Fi, so you don’t need an outdoor sensor. Each brand handles the switch differently:
- Google Nest uses one setting called the Dual Fuel Breakpoint. According to Google’s heat pump configuration guide, it’s in the Google Home app under the thermostat’s Settings, then Equipment. The default is 30°F, and you can set it from 10°F to 50°F, or choose Always or Never. Nest’s Heat Pump Balance feature, which adjusts the lockout for you, isn’t available on dual fuel systems.
- ecobee uses two outdoor temperatures. Compressor Min Outdoor Temperature is where the heat pump stops and the furnace takes over. Aux Heat Max Outdoor Temperature is the warmest temperature at which the furnace is allowed to run at all. Between the two, the heat pump runs first, and the thermostat switches to the furnace only when the heat pump can’t keep up. You set both on the thermostat itself (Main Menu, Settings, Installation Settings, Thresholds), not in the app.
- Sensi switches automatically. Sensi’s spec sheets say it controls dual fuel “without an outdoor sensor,” and that you need to add a fossil fuel kit at the furnace if you want a balance point you can set yourself.
Which Smart Thermostats Support Dual Fuel
Here’s how the current smart thermostats from the major brands handle a dual fuel system, based on each manufacturer’s own compatibility pages and manuals.
| Thermostat | Dual fuel | Largest dual fuel system | How it switches |
|---|---|---|---|
| ecobee Smart Thermostat Premium | Yes | Two-stage heat pump + two-stage furnace | Two outdoor temperature thresholds |
| ecobee Smart Thermostat Enhanced | Yes | Two-stage heat pump + one-stage furnace | Two outdoor temperature thresholds |
| ecobee Smart Thermostat Essential | Yes | One-stage heat pump + one-stage furnace | Not stated |
| Nest Learning Thermostat (4th gen) | Yes | Two-stage heat pump + two-stage furnace | Dual Fuel Breakpoint |
| Nest Thermostat | Single-stage only, needs a C wire or Nest Power Connector | One-stage heat pump + one-stage furnace | Dual Fuel Breakpoint |
| Sensi Touch 2 | Yes | Two-stage heat pump + two-stage gas furnace | Automatic |
| Honeywell Home X8S, X7S, X7B | No | Electric backup heat only | Not supported |
| Amazon Smart Thermostat | No | Not supported | Not supported |
Honeywell is the brand that confuses people most. Its current X series thermostats list “heat pump systems with electric backup heat,” and their setup menu lets you choose a gas or oil furnace as the backup. But Honeywell’s manual says the thermostat “only supports electric backup,” and it warns that the thermostat isn’t compatible if you pick anything else. Honeywell’s dual fuel models are sold through HVAC contractors (the ElitePRO S1200 now, and the discontinued T10 Pro). The T6 Pro TH6320 models (Wi-Fi, Z-Wave and non-Wi-Fi) also handle dual fuel with an outdoor sensor, and our Honeywell T6 Pro review covers each one. Our guide to the best Honeywell thermostats covers the rest of the lineup.
Google publishes the clearest table of any brand: its Nest compatibility page lists each dual fuel layout by model. For ecobee, the main difference between models is staging, which our ecobee Essential vs Enhanced vs Premium comparison explains.
What to Look For in a Dual Fuel Heat Pump Thermostat
When you shop for a dual fuel heat pump thermostat, these are the details that decide whether it works with your system:
- Enough stages. Count the stages on both pieces of equipment, and check that the thermostat supports that many. Some heat pumps and furnaces are two-stage. The ecobee Premium, the Nest Learning Thermostat and the Sensi Touch 2 handle two stages on both sides.
- Control over the switchover. If you know your heat pump’s limits and your energy prices, a thermostat that lets you set the switchover temperature (ecobee, Nest) gives you that control. If you’d rather not touch it, Sensi decides for you.
- A C wire. Check for one before you buy. The Sensi Touch 2 always needs a C wire, and the Nest Thermostat needs one or the Nest Power Connector on a dual fuel system. ecobee includes an adapter in the Premium box. Our C-wire adapter guide explains the options.
- A dual fuel kit at the furnace. Some systems have a dual fuel kit installed at the furnace (Goodman calls it an All Fuel kit, others call it a fossil fuel kit), often with its own outdoor thermostat. If yours has one, check how it’s wired with your installer before you replace the thermostat.
- Professional setup. Google recommends a professional for dual fuel systems. If you’ve never wired a heat pump thermostat, the cost of a professional install is small next to the cost of a wrong setting.
The Best Dual Fuel Thermostats
These four thermostats support dual fuel and are sold by Amazon.com. They’re listed from the most capable to the most affordable.
ecobee Smart Thermostat Premium — Best Overall
The best dual fuel thermostat for most homes, with two-stage support on both the heat pump and the furnace and the most control over when each one runs.
Best for: Dual fuel systems with a two-stage furnace, and anyone who wants to fine-tune the switchover.
What stands out in real use
The Premium’s two outdoor thresholds give you three temperature bands instead of one switchover point: the heat pump alone in mild weather, the heat pump first with the furnace as a backup in cool weather, and the furnace alone in the cold. That suits a heat pump that can still do most of the work around freezing. It comes with a SmartSensor for a second room, and its built-in radar and air quality monitor make it the most complete thermostat here. This bundle adds two door and window sensors.
Key specs
- Heat pumps with two compressor stages plus two stages of aux heat
- Conventional systems up to two heating and two cooling stages
- SmartSensor and Power Extender Kit in the box
- Works with Apple Home, Alexa (built in), Google Home and SmartThings
Pros
- Two outdoor thresholds for precise control of the switchover
- Handles a two-stage heat pump with a two-stage furnace
- Includes a room sensor and a C-wire adapter
Cons
- The most expensive option here
- Thresholds are only on the thermostat, not in the app
- Doesn’t support Matter
Installation and compatibility notes
At setup, choose a heat pump with a furnace as the backup heat, then set Compressor Min Outdoor Temperature and Aux Heat Max Outdoor Temperature under Installation Settings, Thresholds. A utility’s ecobee setup guide for dual fuel also tells you to turn off aux heat simultaneous operation, so the heat pump and furnace never run together. Use ecobee’s compatibility checker if you’re not sure about your stages.
Price: ~$320 (Comfort and Security Bundle with 2 door and window sensors)
Google Nest Learning Thermostat (4th Gen) — Best for Google Home
The Nest that supports every dual fuel layout in Google’s table, with a simple single breakpoint and native Google Home control.
Best for: Google Home users and two-stage dual fuel systems.
What stands out in real use
Google lists the 4th gen as compatible with single-stage and two-stage heat pumps paired with single-stage or two-stage furnaces. The switchover is one setting, the Dual Fuel Breakpoint, which you can change from the Google Home app. It learns your schedule over time and comes with a Nest Temperature Sensor for a second room. However, Google says dual fuel needs advanced configuration and wiring, and it recommends a professional install.
Key specs
- Heat pumps up to three stages, plus one or two stages of aux heat
- Dual fuel up to a two-stage heat pump with a two-stage furnace
- Nest Temperature Sensor (2nd gen) included
- Google Home app, plus Apple Home and Alexa through Matter
Pros
- Supports every dual fuel layout Google lists
- Breakpoint is easy to change in the app
- Needs a C wire or Nest Power Connector in under 1% of homes, according to Google
Cons
- Heat Pump Balance doesn’t work on dual fuel systems
- Only one switchover point, without a middle band
- Google recommends a pro for dual fuel setup
Installation and compatibility notes
The setup happens on the thermostat and in the Google Home app. Choose dual fuel during setup, then check the Dual Fuel Breakpoint under Settings, Equipment (the default is 30°F). Our Nest Thermostat vs Nest Learning Thermostat comparison covers the other differences between the two models.
Price: ~$280 (with Nest Temperature Sensor)
Sensi Touch 2 — Best Automatic Switchover
A thermostat that handles dual fuel on its own logic, without a switchover setting to get wrong.
Best for: Owners who want dual fuel to work without adjusting thresholds.
What stands out in real use
The Sensi Touch 2 switches between the heat pump and the gas furnace by itself. Sensi’s spec sheets say it controls dual fuel without an outdoor sensor, and its installer menu lets you set a one- or two-stage heat pump outdoors with a one- or two-stage gas furnace indoors. You can’t choose the switchover temperature, though. If you want a fixed balance point, Sensi says to add a fossil fuel kit at the furnace. The color touchscreen is easy to read, and it works with Sensi room sensors.
Key specs
- Heat pumps up to four heating and two cooling stages
- Dual fuel with a one- or two-stage gas furnace
- Color touchscreen
- Works with Alexa, Google Home and SmartThings
Pros
- Automatic dual fuel control, nothing to set
- Supports two stages on both the heat pump and the furnace
- Room sensors available
Cons
- You can’t set the switchover temperature
- Always needs a C wire
- Doesn’t work with Apple Home or Matter
Installation and compatibility notes
In the installer menu, set Outdoor Equipment to HP1 or HP2 and Indoor Equipment to GA1 or GA2 for a one- or two-stage gas furnace. The Sensi Touch 2 requires a C wire on every system, so check for one before you buy.
Price: ~$185
Google Nest Thermostat — Best Budget
The lowest-priced option here, for the simplest dual fuel setups only.
Best for: A single-stage heat pump with a single-stage furnace, on a budget.
What stands out in real use
The Nest Thermostat supports one dual fuel layout: a single-stage heat pump with a separate single-stage furnace. For that setup, it uses the same Dual Fuel Breakpoint as the Learning model, in the Google Home app. Google says it needs a C wire or a Nest Power Connector on a dual fuel system. It doesn’t learn your schedule and doesn’t work with Nest Temperature Sensors, but at this price it covers the basics.
Key specs
- Dual fuel: single-stage heat pump with a single-stage furnace only
- C wire or Nest Power Connector required for dual fuel
- Google Home app, plus Apple Home and Alexa through Matter
- Two AAA backup batteries
Pros
- The most affordable option here
- Same breakpoint setting as the Learning Thermostat
- Matter support
Cons
- No two-stage heat pumps or two-stage furnaces
- Needs a C wire or Power Connector on dual fuel
- Doesn’t support remote sensors
Installation and compatibility notes
Check your stages before you buy: if your heat pump or furnace is two-stage, choose the Nest Learning Thermostat instead. If there’s no C wire, the Nest Power Connector installs at the furnace. Our Nest installation guide walks through the wiring.
Price: ~$130
Common Setup Mistakes
Most dual fuel problems come from the setup, not the thermostat:
- Setting it up as electric aux heat. If you tell the thermostat your backup is electric, it can run the furnace and heat pump together, which dual fuel systems aren’t designed for. Choose the furnace, dual fuel or gas option.
- A switchover that’s too high. If the furnace runs on every cool morning, your heat pump isn’t doing as much of the heating as it could. Lower the breakpoint a few degrees at a time and check that the house stays comfortable.
- A switchover that’s too low. If the heat pump runs for hours on the coldest days and the house still feels cool, raise it.
- Ignoring a dual fuel kit. If your system has a dual fuel kit at the furnace, ask your installer how the thermostat should be set up before you change any switchover setting.
- Using emergency heat as a fix. Emergency heat runs only the furnace. Use it if the heat pump has failed, and call a technician.
Conclusion
A dual fuel thermostat has one job a regular thermostat doesn’t: deciding when the furnace should take over from the heat pump. The ecobee Premium gives you the most control and handles two-stage equipment on both sides. The Nest Learning Thermostat supports every dual fuel layout with a simple breakpoint, the Sensi Touch 2 handles the switch on its own, and the Nest Thermostat covers single-stage systems for less. Avoid Honeywell’s X series and the Amazon Smart Thermostat for dual fuel. For heat pumps with electric backup, see our guide to the best thermostats for heat pumps, and for everything else, the best smart thermostats.
What is a dual fuel thermostat?
A dual fuel thermostat controls a heat pump paired with a gas, propane or oil furnace. It runs the heat pump in mild weather and switches to the furnace when the outdoor temperature drops below a switchover point, so only one of them heats at a time.
Does the Nest thermostat work with dual fuel?
Yes. Google lists the Nest Learning Thermostat (4th gen) as compatible with every dual fuel layout in its table, up to a two-stage heat pump with a two-stage furnace. The Nest Thermostat supports only a single-stage heat pump with a single-stage furnace, and it needs a C wire or a Nest Power Connector for it.
Does the Honeywell X8S support dual fuel?
No. Honeywell’s manual says the X8S, X7S and X7B support heat pumps with electric backup heat only, and the thermostat warns that it isn’t compatible if you choose a gas or oil furnace as the backup. Honeywell’s dual fuel models, such as the ElitePRO S1200, are installed by HVAC contractors.
What temperature should a dual fuel heat pump switch to gas?
It depends on your heat pump and your energy prices. The U.S. Department of Energy’s building science training puts the switchover between 5°F and 35°F depending on the equipment, and Nest’s Dual Fuel Breakpoint defaults to 30°F. A cold-climate heat pump can usually run lower, especially where electricity is cheap compared to gas.
Can ecobee thermostats run a dual fuel system?
Yes. ecobee says its thermostats work with dual-fuel heat pumps. The Premium handles a two-stage heat pump with two stages of backup heat, the Enhanced one backup stage, and the Essential a single-stage heat pump with one backup stage. You set the switchover with two outdoor temperature thresholds on the thermostat.
Do I need an outdoor sensor for a dual fuel thermostat?
Usually not. Nest uses local weather over Wi-Fi to know the outdoor temperature, and Sensi says its thermostats control dual fuel without an outdoor sensor. Some systems have a dual fuel kit at the furnace with its own outdoor thermostat, so check with your installer if yours does.
Written by Evan Mercer
Founder & Lead Researcher, Smart Home Matrix
Evan digs through spec sheets, firmware changelogs, and thousands of owner reviews so you don’t have to. Every guide starts with a compatibility check and ends with picks he would install in his own home. Read more about Evan and this site, or see exactly how we choose products.