Understanding dual-fuel HVAC systems and when they’re worth it

If you’ve ever wondered about a dual fuel or hybrid HVAC system, it is a system that has the ability to heat your home using electricity or natural gas, providing the opportunity to maximize efficiency and comfort. A dual-fuel heating system automatically switches between a heat pump and a gas furnace depending on the outdoor temperature. The temperature at which the system switches is adjustable and can be based on capacity or efficiency using whichever one is more important for the customer.

What is a dual-fuel HVAC system?

A dual-fuel system is made up of four components: a heat pump, indoor coil, furnace, and thermostat. Here’s how each one contributes to your home comfort.

• Electric heat pump: Sits outside and contains the compressor, coil, and fan that absorb or reject heat that is then transferred to the indoor coil, which sits on a gas furnace that uses its blower to move the conditioned air throughout the home.
• Gas furnace: Burns gas creating heat that is distributed throughout the home using its built-in blower.
• Smart thermostat: Acts as the control center, monitoring Indoor and outdoor conditions to decide when the heat pump or furnace should run and how.
• Indoor Coil: Works with the Heat Pump, which is located outdoors. The indoor coil removes heat from the home in cooling mode and adds heat to the space in heating mode using the gas furnaces built-in blower to move the conditioned air throughout the home.

How dual-fuel systems work 

The furnace and heat pump share one thermostat that decides when and which energy source to use.

• Mild or cool weather: Uses the heat pump because it’s typically more efficient than a gas furnace when outdoor temperatures are moderate.
• Cold weather, as we all know cold is a relative term.  All heat pumps' heating capacity decreases as the outdoor temperature decreases. Today's heat pumps can provide efficient heat output at much lower outdoor temperatures than previous designs. The Navien NAZ-17 heat pump can provide heat down to minus 4 degrees F.  The system can be configured to switch to gas heat based on Heat pump capacity at a pre-selected outdoor design temperature.  The switch can also be based on operating efficiency, where it is cheaper to use gas heat than heat pump heat. These are decisions that need to be determined in order to properly configure the system to optimize efficiency and comfort.
• Hot weather: The heat pump runs in reverse to cool your home, working just like a central air conditioner where the furnace moves air throughout the home, and the indoor coil absorbs the heat energy and transfers it to the outdoor section of the electric heat pump to discharge the heat energy absorbed from the conditioned space.

For typical installations in moderately cold weather, the heat pump handles most of the heating, though the thermostat may call on the furnace for a short time to speed up heating. When temperatures plunge, the furnace can take over completely to keep your home warm without wasting energy. This automatic switching ensures consistent comfort and lower energy use year-round.

Benefits of a dual-fuel HVAC system

When installed and configured correctly, a dual-fuel system offers several benefits:

High efficiency and lower utility bills
The system can be configured to use the most efficient energy source, saving money compared to relying on gas or electric alone.

Year-round comfort
Your home stays comfortable whether it’s freezing, scorching, mild, or changing by the hour.

More comfortable indoor air
The heat produced by heat pumps is less dry than the heat from most gas furnaces (our NPF hydro-furnace is less drying than others because it doesn’t expose the airstream to the extreme temperatures of a typical gas furnace heat exchanger. Having a heat pump in the mix reduces the winter dryness that can irritate your skin and sinuses.

Environmentally friendly
Because electricity can be sourced from renewable energy, dual-fuel systems may reduce fossil fuel use and your home’s carbon footprint. This is especially true if you have solar panels.

Built-in backup
If one component needs service, the other can often keep your home comfortable until repairs are made. Having a safety net for home heating is always smart, particularly for those living in remote areas.

When is a dual-fuel system worth it?

A dual-fuel system makes the most sense if you live in a region with a wide range of temperatures: hot summers, cold winters, and fluctuating spring and fall conditions.

Dual-fuel may be worth the investment if:

• Your home already has a natural gas connection.
• You live in an area where both electricity and gas prices are subject to change.
• You use significant heating and cooling energy throughout the year.
• Your winters are cold, but not the most extreme. This is ideal for letting the heat pump handle regular cold days while the furnace handles deep-freezes.
• You have solar panels that can offset the heat pump’s electricity use.

Dual-fuel options from Navien

Navien offers a full suite of high-efficiency residential HVAC units, including a dual-fuel compatible furnace and heat pump.

NPF Hydro-furnace

The Navien NPF hydro-furnace is an ultra-efficient gas furnace featuring variable capacity operation from 15–100%, so it dynamically adjusts airflow and heat output to match your home’s heating demand. It’s a reliable part of a dual-fuel heating system when paired with any AHRI-matched heat pump.

NAZ Heat Pump

The Navien NAZ heat pump provides high-efficiency, precise, capacity-matching heating and cooling for year-round comfort. It automatically adjusts output based on your home’s HVAC load and is dual-fuel compatible, ensuring efficient performance in any climate.

Dual-fuel HVAC FAQ

If you have more questions about dual-fuel HVAC, we have answers.

How can I tell if my HVAC system is dual fuel?

If you’re not sure what type of HVAC system you have, look for these clues:

• There’s a gas furnace indoors and a heat pump unit outside. A heat pump looks similar to a central A/C condenser, so check the manufacturer’s data label for the words ‘heat pump’ or search the model number online if you’re not sure.
• If you have a gas furnace and your thermostat has settings for auxiliary or emergency heat. This indicates dual-fuel or hybrid capability.
• Confirm by asking your realtor or HVAC technician.

Why not just use a heat pump alone?

If you live in a region with mild winters, a heat pump by itself can be an excellent all-in-one solution. But in colder climates, heat pumps become less efficient as temperatures drop. A dual-fuel setup lets the heat pump handle moderate weather while the furnace takes over during spells of deep cold, providing faster, more efficient heating when you need it most.

What thermostat works best with a dual-fuel system?

Use a smart or programmable thermostat designed to control both a furnace and a heat pump. Key features to look for include:

• Dual-fuel support: Must be designed to manage both heat pump and furnace operation.
• Balance-point control: Lets you set the outdoor temperature at which the system switches from the heat pump to the furnace (often around 40°F, though different factors can affect the optimal cutoff temp).
• Smart energy features: Some thermostats can adjust heating and cooling usage based on current local utility rates or Time-of-Use plans for extra savings.
• Remote access: Control temperature settings and schedules from your phone.

How long does a dual-fuel HVAC system last?

Because the furnace and heat pump share the heating load, each component experiences less wear. With proper installation and maintenance, a dual-fuel system can last 20-25 years or longer.

What homes aren’t suited for dual fuel?

Homes without existing gas lines usually aren’t good candidates since it makes installation expensive. Dual-fuel is also unnecessary in very warm climates where a heat pump alone provides enough heating and cooling year-round. 

Even if dual fuel isn’t right for your home, Navien’s NPF Hydro-Furnace and NAZ Heat Pump each deliver exceptional efficiency and comfort on their own.

Who can install a dual-fuel HVAC system?

Always hire a certified HVAC technician trained in Navien’s advanced systems to ensure proper installation and protect your warranty. Dual-fuel systems require more expertise than a standard system replacement, since the heat pump, furnace, and smart thermostat must work together seamlessly for optimal efficiency.

Not every contractor is experienced with modern heat pump technology, and some may steer homeowners toward traditional furnaces simply because that’s what they know best. Proper sizing, setup, and ductwork are critical; if any part is off, you could end up with noise, drafts, or poor comfort conditioning performance that isn’t the equipment’s fault.

To get the best results, choose a professional who understands dual-fuel systems and is familiar with Navien’s products. You can easily find qualified local installers using Navien’s installer and service locator.