Here's the lowdown on the most common types of furnaces found in U.S. homes, and how to identify them.
5 Types of Furnaces and How to Identify Them
Why Are There So Many Types of Furnaces?
Most American homes rely on a furnace to provide warmth in cold weather. And because different homes have different budgets and needs, there are several types in use across the country.
Complicating matters a little more, many people are fuzzy about what exactly a furnace is. The Merriam-Webster Dictionary tells us a furnace is “an enclosed structure in which heat is produced.”
However, homeowners often use “furnace” in a more causal way, to describe their entire heating, ventilation and air conditioning (HVAC) system. And when pros say “furnace,” they’re referring to a specific type of heating.
To sort this all out, we contacted a pair of experts. Jeff Gervais, president of Gervais Mechanical, and Josh Mitchell, an HVAC technician and owner of airconditionerlab.com, walked us through the most common types of furnaces, how to identify them and what to consider if you’re looking to purchase one.
According to our experts, furnaces vary based on three main factors:
- The fuel types available in a given area;
- The local utility rates;
- The local climate.
So let’s learn about the different types of furnaces!
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Gas Furnace
Gas furnaces generate heat by burning natural gas. They’re available in varying sizes and energy efficiencies and produce a hot, dry heat. While still the most widely used furnaces, they’re starting to lose market share to electric models due to utility costs, environmental concerns and tax incentives.
Mitchell says gas furnaces are an excellent choice in regions with harsh winters due to their powerful heating capacity. He suggests looking at more than just the initial price when selecting a furnace. “Gas furnaces might have higher installation costs,” he says, “but they generally offer lower monthly running costs.”
Gervais agrees. Gas furnaces, he says, are “a smart choice in regions with cold climates and affordable natural gas.” He adds they “require a connection to the gas supply and regular maintenance to ensure safety and efficiency.”
How to identify a gas furnace
It’s easy: You’ll see a gas supply line and exhaust flues. Low-efficiency gas furnaces will vent to the roof, while higher efficiency models vent out to an exterior wall.
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Electric Furnace
Unlike gas furnaces, electric furnaces don’t use an open flame. “Electric furnaces use electricity to generate heat and are typically the simplest in terms of installation and maintenance,” says Gervais. They’re best suited for areas with mild winters or high gas utility rates.
“Electric furnaces are a good option where natural gas isn’t available,” Mitchell says. “They’re cheaper to install, safe and have a longer lifespan but can lead to higher energy bills, especially in colder climates.”
Gervais says electric furnaces are appealing for their safety. “There’s no need to worry about gas or oil leaks,” he says. “Electric furnaces are generally considered more environmentally friendly, especially if the electricity comes from renewable sources.”
How to identify an electric furnace
These are the only ones that don’t require a flue or vent line. When they kick on, there’s no visible flame.
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Oil Furnace
Oil furnaces burn an external fuel called fuel oil to generate heat. Fuel oil is similar to diesel gas, and some models burn kerosene.
Mitchell says oil furnaces are popular in areas where other fuels aren’t readily available. “[Oil furnaces] are known for their high heat output.” he says. “However, they’re less efficient and more expensive to run than gas furnaces and require more maintenance.”
How to identify an oil furnace
Look for an external fuel tank that’s metal or poly-coated metal. Most fuel oil tanks are a flattened oval. Viewed from the end, they resemble a typed zero (0).
Some fuel oil tanks are double-walled, with a rectangular case wrapped around the traditional tank. Gervais says your nose may tell you a furnace is oil-powered because of the distinct oil smell if there are leaks or issues.
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Propane Furnace
Propane furnaces are similar to gas furnaces but run on propane rather than natural gas. Like oil furnaces, propane furnaces are identifiable by their external fuel tank.
While propane furnaces can technically run on the small 20-pound tanks commonly used with gas grills, they’re more likely to have 500 -to 2,000-pound tanks that can heat a home for months before needing to be refilled.
Propane furnaces can be installed anywhere. They’re most often found in homes that lack natural gas lines but can be accessed by refilling trucks.
“While propane generally costs more than natural gas,” says Gervais, “propane furnaces can be more efficient.” But storage tanks must be refilled regularly, he says, and homeowners need to factor in the logistics and cost of delivery.
How to identify a propane furnace
The propane tank will be somewhere on the property. Look for a metal cylinder, usually horizontal. (It looks like a big hot dog.)
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Wood Burning Furnace
Wood burning furnaces are fueled by seasoned firewood or pellets.
Although far less common than the other furnaces on this list, you can still purchase a new wood burning furnace online or at many home improvement centers. Some models require electricity to operate the thermostat or turn a pellet hopper.
How to identify a wood burning furnace
The most straightforward indicator will usually be a significant quantity of seasoned wood or pellets.
Because they use an open flame, all wood burning furnaces have some kind of flue system. Some are intended to be installed outdoors, usually in a shed. This simplifies venting smoke and carbon monoxide, as well as cleanup, although it does require a trip outdoors to restock the wood.
Bonus: What Is Not a Furnace?
Although often discussed in the same conversation, heat pumps and boilers are not technically furnaces.
Heat Pump
Furnaces warm homes by generating heat through electrical resistance or burning fuel, while heat pumps draw pre-existing ambient heat from outside and shift it into your home.
In colder climates, heat pumps are often paired with a furnace to supplement heating. These “dual-fuel” systems switch over to a traditional furnace when the temperature gets cold enough to tax the heat pump.
How to identify a heat pump
Heat pump exterior units resemble a standard air conditioner, but tend to be larger. If a home heats up in chilly weather without the furnace kicking on, it has a dual-fuel system.
Boiler
Boilers also aren’t furnaces. Although they generate heat in an enclosed space, they heat water rather than air.
How to identify a boiler
If a home has radiators, then it has a boiler rather than a furnace. Boilers themselves are connected to pipes rather than air ducts, and typically sit lower than furnaces.
Helpful Tips For Buying the Best Furnace for Your Home
To help you choose the best furnace to buy for your home, here are some buyer’s guidelines to consider before picking one out.
- Best Furnace Brands
- Gas Furnace Buying Guide
- Complete Wall Furnace Guide
- Oil Furnace Buying Guide
- Electric Furnace Buying Guide
- Hydronic Baseboard Heater Buying Guide
- Choosing a Home Heating System
About the Experts
- Jeff Gervais has been president of Gervais Mechanical Services for two decades. Gervais and his team, with more than 100 years of combined experience, offer solutions for any commercial or residential project, no matter the size or complexity.
- Josh Mitchell is an HVAC technician and the founder of airconditionerlab.com, a website that helps people solve their HVAC problems.
