Heat Pump or Gas Furnace? How Each One Heats a Phoenix Home

An air-source heat pump heats your home by moving heat from the outdoor air into the house. It uses the same outdoor unit that cools you all summer. A gas furnace makes its own heat by burning natural gas inside the unit and then blowing the warm air through your ducts.

They work in different ways, and each one needs different care. At Viking Heating & Air Conditioning, we work on both kinds of systems in homes across the East Valley.

How Does a Heat Pump Heat a Home?

A heat pump doesn't burn fuel to make heat. Instead, it moves heat from one place to another. An electric air-source heat pump uses the difference between the outdoor and indoor air temperatures to cool and heat your home. In summer it carries heat out of your house, and in winter it reverses direction and brings heat in.

ENERGY STAR suggests a helpful way to picture it. You can think of a ducted air-source heat pump as "a central air conditioner that also works in reverse to provide whole-house space heating in winter." In other words, the outdoor unit and indoor unit that cooled your home through the summer are the same equipment that warms it on a chilly night.

Not every heat pump uses ducts. Several types of heat pumps are available, including air-source, geothermal, ductless mini-split and absorption models. A ductless mini-split heats and cools without ductwork. Most of this guide deals with ducted air-source systems, since that is the setup being compared with a gas furnace.

Living With a Heat Pump in Winter

Heat pumps also have a backup. They rely on a secondary heating source when outdoor temperatures drop dramatically.

Some thermostat habits that suit a furnace don't suit a heat pump. With a heat pump, stick with a steady temperature. Unlike a furnace or boiler, a heat pump does not save energy when you turn it down while you're away or asleep. It also helps to keep the system set to "heat" or "cool" instead of Auto, so it doesn't switch back and forth between modes on an unseasonably warm or cold day.

Key Takeaway: A heat pump moves heat instead of burning fuel, and the same equipment handles both summer cooling and winter heating. ENERGY STAR advises a steady thermostat setting, because a heat pump does not save energy by being turned down when you're away or asleep.

How a Gas Furnace Heats Your Home

A gas furnace makes heat by burning fuel. In a natural gas furnace, gas is mixed with air inside a burner and lit inside the combustion chamber. A blower pulls cooler air in from your rooms. That air is heated as it passes over a heat exchanger connected to the combustion chamber, and the warm air then flows back into your rooms through the ductwork.

A furnace also has to get rid of the gases the burners produce. The exhaust is vented outside through a flue in the roof or, on some models, through a side wall vent. A flue is a vent pipe that carries exhaust out of the house. Because the furnace only heats, a separate central air conditioner with its own outdoor unit handles the cooling, and a traditional furnace operates entirely indoors, so the outdoor AC unit stays silent through the winter.

The two systems also differ in how much they warm the air. In our technicians' experience, a gas furnace's flame can heat the air passing through it by up to about 50 degrees Fahrenheit. A heat pump, which works like your air conditioner running in reverse, can heat that air by up to about 30 degrees Fahrenheit.

Burning fuel comes with specific safety steps. To prevent carbon monoxide (CO) poisoning from heating equipment, the U.S. Consumer Product Safety Commission (CPSC) "urges consumers to schedule a yearly professional inspection of all fuel-burning home heating systems." That list includes "furnaces, boilers, fireplaces, wood stoves, water heaters, chimneys, flues and vents." In its carbon monoxide guidance, CPSC also says to "Install battery-operated CO alarms or CO alarms with battery backup on every level of the home and outside sleeping areas."

Key Takeaway: A gas furnace makes heat indoors by burning natural gas, vents its exhaust outside through a flue, and relies on a separate air conditioner for summer. Because it burns fuel, it falls under CPSC's call for a yearly professional inspection of all fuel-burning home heating systems.

Which One Is in Your House?

These four checks can help you tell which system you have without opening any panels:

1. Check the thermostat. If your thermostat has settings labeled "EMER" (emergency heat) or "AUX" (auxiliary heat), you almost certainly have a heat pump. A traditional furnace and air conditioning setup will not have these settings.
2. Watch the outdoor unit with the heat on. Set the thermostat to heat and raise the temperature enough to start the system, then step outside. If the fan in the outdoor unit is running and blowing cold air out the top while your house is being heated, you have a heat pump. With a furnace, the outdoor unit stays quiet.
3. Look at the indoor unit. Find your indoor heating unit and look for a gas pipe running to it and a vent pipe leaving it. A gas furnace vents its exhaust outside through a flue, either through the roof or, on some models, through a side wall. So a gas pipe and a flue at the heating unit point to a gas furnace.
4. Consider an electric furnace. If you find no gas pipe and no flue at the heating unit, it isn't venting combustion exhaust, so your heat is likely electric. It could be a heat pump (see checks 1 and 2) or an electric furnace. AHRI describes an electric furnace as a unit that "uses a blower unit to blow air over electrically-heated coils."

A home that shows signs of both systems has a heat pump and a gas furnace. That combination is a dual-fuel setup, which the next section covers. If you're still unsure after these checks, a technician can tell you on the next visit.

Key Takeaway: AUX or EMER on the thermostat, or an outdoor fan running while the house heats, points to a heat pump. A gas pipe and a flue at the indoor unit point to a gas furnace.

Dual-Fuel Systems: A Heat Pump and a Furnace Together

A dual-fuel system pairs a heat pump with a gas furnace in the same home. ENERGY STAR explains that a dual-fuel system lets you heat with either the heat pump or the furnace. You can use each one where it works best based on costs and environmental benefits.

A heat pump is also worth considering if you have a relatively new furnace with an older central AC, or if you're planning to add new central AC to the furnace. Pairing the two this way creates a dual-fuel system. The heat pump takes the place of the air conditioner and can also share the heating work with the furnace you already have. Because a dual-fuel home has both systems, it can pass the heat pump checks above and will also have a gas pipe and a flue at the indoor furnace.

Choosing Between Them for a Phoenix Winter

Climate is part of the decision. The U.S. Department of Energy states that "In moderate climates, heat pumps can be an energy-efficient alternative to furnaces and air conditioners." That doesn't mean a heat pump is the right answer for every home.

A few questions about your home can help narrow it down. Is your air conditioner also nearing replacement? A heat pump handles both cooling and heating, so an AC that needs replacing can point toward a heat pump.

Do you have a relatively new furnace and an older central air conditioner? If so, consider a heat pump paired with that furnace as a dual-fuel system. What shape are your ducts in? Ducted heat pumps and furnaces both depend on them, while ductless mini-splits don't.

Sizing and setup matter too. A good contractor will work with you to determine the right size and how a heat pump could tie in with a backup heating system in your home. For a wider look at heating options in the Valley, see our complete residential heating guide for Phoenix Valley homeowners. When it's time to replace equipment, our HVAC installation page explains how we approach a new system.

Key Takeaway: The Department of Energy says heat pumps can be an energy-efficient alternative to furnaces and air conditioners in moderate climates. ENERGY STAR suggests considering one if your furnace is relatively new and your central air conditioner is older. A good contractor will help determine the right size for your home.

Getting Either System Ready for Winter

The winter care each system needs follows from how it works. A gas furnace burns fuel, so CPSC's call for a yearly professional inspection of fuel-burning heating systems applies to it.

A heat pump works through both seasons, so it goes into winter after a full summer of cooling. For either type, ENERGY STAR's advice is to "Perform regular maintenance of your heating and cooling system to prevent future problems and unwanted costs." We cover the step-by-step side in two other posts: how to prepare your HVAC system for colder weather in the Phoenix Valley and heating system maintenance during a Chandler winter.

Frequently Asked Questions

Is a heat pump just an air conditioner that also heats?

For a ducted air-source heat pump, largely yes. ENERGY STAR says it may be helpful to think of a ducted air-source heat pump as a central air conditioner that also works in reverse. In winter, that reverse mode provides whole-house space heating. It cools in summer by moving heat out of your home and heats in winter by moving heat in. A home that relies on a heat pump alone uses the same outdoor unit and indoor unit for both seasons, with no separate furnace. In our technicians' experience, a heat pump can heat the air passing through it by up to about 30 degrees Fahrenheit, while a gas furnace can heat it by up to about 50 degrees.

How can I tell if I have a heat pump or a gas furnace?

Start with your thermostat. If it has settings labeled EMER (emergency heat) or AUX (auxiliary heat), you almost certainly have a heat pump. You can also set the thermostat to heat, raise the temperature enough to start the system, and step outside. If the outdoor unit's fan is running while the house is being heated, it's a heat pump. A gas furnace works entirely indoors and has a gas pipe and a flue vent pipe connected to it.

Why is my outdoor unit running when the heat is on?

If you have a heat pump or a dual-fuel system, that's how it's designed to work. The outdoor unit is where a heat pump gathers heat from the outside air before moving it indoors. If the outdoor fan is running and blowing cold air out the top while your house is being heated, you have a heat pump. With a gas furnace and a standard air conditioner, the outdoor unit should stay silent while the heat runs. If you're not sure which system you have, a technician can tell you.

Does a gas furnace need a yearly inspection?

Yes. To prevent carbon monoxide poisoning, the U.S. Consumer Product Safety Commission urges consumers to schedule a yearly professional inspection of all fuel-burning home heating systems. That includes furnaces, boilers, fireplaces, wood stoves, water heaters, chimneys, flues and vents. CPSC also recommends installing battery-operated CO alarms or CO alarms with battery backup on every level of the home and outside sleeping areas.

Should I turn my heat pump down at night or when I'm away?

ENERGY STAR advises keeping a steady temperature. Unlike a furnace or boiler, a heat pump does not save energy when you turn it down while you're away or asleep. It also helps to set the thermostat to heat or cool rather than Auto, so the system doesn't switch back and forth between modes on an unseasonably warm or cold day.

What is a dual-fuel system?

A dual-fuel system pairs a heat pump with a gas furnace in the same home. ENERGY STAR explains that it lets you heat with either the heat pump or the furnace. That way, each one can be used where it works best based on costs and environmental benefits. Because it has both, a dual-fuel home shows signs of each system: an outdoor unit that can run in heating mode, plus a gas pipe and flue at the indoor furnace.

Is a heat pump a good choice for a Phoenix home?

It can be. The U.S. Department of Energy says that in moderate climates, heat pumps can be an energy-efficient alternative to furnaces and air conditioners. The right answer still depends on your home. Is your air conditioner also due for replacement? Do you have gas service and a furnace in good shape? What condition are your ducts in? ENERGY STAR notes that a good contractor will work with you to determine the size and potential integration with a back-up heating system that will work best for your home.

Does a heat pump need a gas line?

An electric air-source heat pump on its own does not. ENERGY STAR explains that heat pumps move heat rather than converting it from fuel the way combustion heating systems do. A gas line only matters for heating if the heat pump is paired with a gas furnace in a dual-fuel system. Your home may still have gas service for other appliances.

Heat Pump, Furnace or Both

A heat pump moves heat and handles both seasons with one system. A gas furnace makes heat by burning natural gas and works alongside a separate air conditioner. A dual-fuel system combines the two. Once you know which one is in your home, it's easier to understand how it behaves in winter, what care it needs, and what your choices are when it's time for a change.

Whether you want help identifying your system or you're starting to weigh a replacement, call Viking at (480) 689-5167 or request a free estimate.