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What Is a Furnace? All Parts and Functions Explained

home furnace

What is a Furnace?

A furnace is a large appliance that heats a home or other building. Furnaces often use gas or electrical power, but can also use oil, propane, wood, or even corn as a fuel source. Some refer to it as a “heater,” but this is a more generic term that can apply to furnaces or other heating devices such as heat pumps or radiators.

Furnaces & Home Heating: What You Need to Know

The definition above may be all you’re looking for, but if you clicked through to this article, I’m guessing you’re looking for a new furnace and want to know more about this important

Furnaces are expensive. They’re also responsible for a lot of you and your family or loved ones’ comfort in the colder months. It pays to know more about them…literally!

Fuel Sources for Furnaces

The first thing to establish about a furnace is what’s fueling it.

The two major fuel sources for furnaces in the US are gas and electric power. We’ll talk a bit about the differences below, and also cover additional types that you may encounter in a home.

There isn’t a “best” fuel source, but a lot will depend on the cost of gas vs. electric in your area and also what your home is equipped to utilize.

How Does a Furnace Work?

We’re going to start by assuming a natural gas home furnace, and explain the differences between it and electric furnaces step by step. Below is a concise summary of the home heating process.

  1. Your thermostat sends a signal to the system that it’s too cold in the house, triggering the heating process.
  2. The metering valve on the gas line opens, emitting enough gas to ignite the burners. In an electric furnace, the coils will begin to heat inside the unit.
  3. The blower motor starts the blower fan and begins to circulate air through the ductwork in your home. This pulls cooler air from the home through return air ducts while pumping the newly heated air through vents.
  4. In a gas furnace, the heat must first travel through a heat exchanger, which separates heat from potentially toxic gasses that are produced in the process. This excess is vented safely through flue pipes, usually through your roof or out the side of your home. Only then does the heat enter the ductwork to be circulated.
  5. This cycle continues until the home is the desired temperature.

By contrast, it’s a simpler process than air conditioning, which we’ve covered previously.

Differences Between a Furnace and a Heat Pump

Heat pumps both heat and cool, and are often installed in conjunction with electric furnaces.

Heat pumps operate by absorbing ambient heat from the air outside your home into a refrigerant line, then transferring it indoors (they do the opposite for cooling).

Furnaces, by contrast, are actually heating the indoor air. Often, heat pumps will provide heat to a home up to a certain temperature, past which the heat from an electric furnace is used as supplemental heat.

Parts of a Furnace

Below is a non-comprehensive list of major parts of your furnace system. It covers major pieces of equipment and subsystems that contribute to heating your home.

Furnace Efficiency: AFUE and Energy Costs

So what makes one furnace better than another?

Assuming it’s been properly sized and is powerful enough to circulate air through your home (a good installer will ensure this), there are still differences in efficiency and comfort.

Electric furnaces are technically 100% efficient. This doesn’t always mean they’re the cheapest, though, because the cost of electricity in your area may be higher than gas.

Entry-level modern gas furnaces are 80% efficient. An easy way to think about this is that 20% of your heating costs (and total heating energy) isn’t going toward heating your home.

High-efficiency gas furnaces can reach up to around 98% efficiency. This is making your money go a lot further!

The flip side to that coin, of course, is that the more efficient furnaces will cost more. Depending on your energy usage and how long you expect to be in your home, it can still be a great investment.

AFUE (Annual Fuel Utilization Efficiency) is a weird acronym that measures this efficiency and rates a furnace’s efficiency.

Cost of a New Furnace

Typical costs range wildly depending on the type of furnace and cost of living where you live.

Many online calculators will typically show average ranges of $3,000 to $10,000, though these often only include the cost of equipment, not labor, which can be significant. Others will cut off the extremes on either end to only talk about averages.

Here in the Sacramento area, furnace costs range from approximately $5,000 to $14,000, and this covers all labor, fees and related costs, such as those for state and local permits.

Furnace FAQs

Below are a handful of questions we frequently get from customers that aren’t covered explicitly in the sections above.

What’s the Difference Between Furnace and Heater?

In practice, there’s often no difference. Many people refer to their furnace as a heater, and this usage will be commonly understood.

In a technical sense, heater is a more general term that could refer to a furnace or several other appliances, such as a heat pump, radiator, water heater, space heater, or fireplace.

How Do I Know if I Have a Gas or Electric Furnace?

There are several ways to tell this. The model number is one, which you can look up. The equipment manual is another. Simply checking to see if it’s connected to a gas line and has burners for heating is another. Worst case, if it’s in a hard-to-reach area and perhaps you don’t have the model number or manual handy, you can speak with an HVAC professional who can inspect, diagnose and answer any questions you may have.

Which is Better: Gas or Electric Furnace?

There isn’t a single right answer to this question, but it depends on where you live and what you use heating for. Some areas have extremely high cost of electricity, so gas is the clear choice. Some will even convert their system from electric to gas to avoid the high energy bills.

Other times, your home isn’t set up for gas heating, and the cost of installing a gas line and running natural gas to it will be prohibitive. In these instances, electrical will be the better option.

Are There Alternatives to a Furnace?

Yes, and we covered several above. However, many are ill-equipped to heat an entire home. Individual radiators or space heaters, or built-in features like fireplaces, are good for heating individual areas, but struggle to heat an entire home. The same goes for ductless options, though these can be a cost-effective way to fully heat a smaller area.

Getting the Most From Your Home Furnace

So now you know more about your home furnaces: types, efficiency levels, costs, and which might be best for your home.

The next step is to contact a trusted heating and cooling specialist for a free home consultation where they walk you through your options for a new furnace, air conditioner or other home comfort equipment.

And if this article was helpful, we hope your first call is to CABS! Our experts will never pressure you into any sale, we have options for every home and budget, we have a range of financing options, discounts and rebates through state and federal groups, and will never charge you to provide a comprehensive quote on new installations. Reach out today!

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