
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.
- Natural Gas – one of the more popular and cost-effective fuel sources for furnaces. A working gas line needs to exist in the home for a gas system to work.
- Electrical – An electric furnace isn’t exactly a furnace in the traditional sense, but an air handler that’s been fitted with electric heating coils. It honestly works a bit like a large toaster oven, although that simplifies a lot of other processes taking place.
- Oil – Oil furnaces are more common in rural areas without as much natural gas infrastructure. Keeping them clean can be an issue, though they produce reliable heat.
- Wood and Corn Furnaces – these simply burn the titular fuel for heat. They tend to exist in homes not fitted for central air systems that you’ll find in most modern homes.
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.
- Your thermostat sends a signal to the system that it’s too cold in the house, triggering the heating process.
- 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.
- 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.
- 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.
- 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.
- Blower Motor & Fan – this is what moves the air through your ductwork and filter. Proper power, calibration, and steady airflow (not clogged) is vital for proper heating.
- Burners – In a gas furnace, the burners are ignited to provide heat.
- Combustion Chamber – houses the burners to keep the flames separated from other sensitive parts of the system.
- Control Board – this usually sits on the outside of the primary heating unit and controls various smaller parts that need to coordinate to produce heat in the home. It is then connected to the thermostat and communicates with it to gauge heating need.
- Ductwork – not only for heating, of course, but without sufficient, sealed and insulated ductwork, the heating efficiency in your home would be far worse.
- Filter – air travels through your air filter as it circulates through the ductwork, before returning to the home once it’s been heated. A clean, quality filter is one of the most important parts of your entire HVAC system.
- Flame Sensor – a safety and functionality device designed to detect flame and gas line emissions.
- Gas Line – the natural gas line running to your home and system in gas-fueled furnaces.
- Heat Exchanger – in a gas furnace, the heat exchanger separates heat from waste gasses that are ventilated safely outside of your home. The most efficient furnaces will have a secondary heat exchanger to separate even more heat and send it to your home.
- Igniter – ignites the burners in a gas furnace
- Plenum – most systems actually have a supply and return plenum, both of which house air and supply it either to the ductwork or the central heating system. A correctly sized plenum is necessary for your heater to work as intended.
- Return Air Drop – also a part of the ductwork that is usually the widest portion of the duct line and connects to the heating unit.
- Thermostat – the brains of the operation. A correctly set up thermostat monitors and controls heating in 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!