What is a Furnace?

by Jan 26, 2021Furnace

History of the Furnace

The first furnace was recorded to have existed in 15 AD. Yeah, that long ago! The word “furnace” comes from the Greek/Latin root “fornax,” meaning oven. Back then, furnaces only relied on wood to heat building spaces during the cold season. It wasn’t until 1855 when Russian-Polish inventor Franz San Galli invented the first “modern” heating furnace. Around that time, the cost of coal became affordable thanks to another pioneer of heating, Dave Lennox.

By 1919, Alice Parker had patented the first American heating system — the wall furnace! Since then, we’ve built and expanded on our modern heating technology. We are now able to offer several different models and furnace designs that run off of 5 major fuel types… but we’ll get into those later.

So what does a furnace do? And how does it work? 

A furnace is a central heating unit that expels heat into your space. 

In most furnace systems, there are at least five key components.

  1. The thermostat
  2. The burners
  3. The blower
  4. The heat exchanger
  5. The home ductwork

In gas furnaces, the thermostat is in charge of signaling to the unit when to begin a heating cycle. Once the thermostat has been switched on, the fuel valve opens and allows the fuel to flow into the burners and be ignited. This heat moves into the heat exchanger and creates hot air. The blower then moves the hot air into your home ductwork and voila! The heating process begins.

Types of Furnaces

So far we’ve mentioned gas furnaces, but what other types of furnaces are out there for you to choose from?

Well, furnaces come with a variety of different features. From system designs, to models, to fuel types, there are LOTS of different furnace options. This can make it difficult to figure out which one is right for you.

Let’s start with the basics: the System Design.

There are 3 furnace designs.

  1. The Package Design
  2. The Split Design
  3. The Stand-Alone Design
  1. The Package: this furnace design combines multiple HVAC units (such as your air conditioner and furnace) into one single unit. It shares your home ductwork, and is typically housed outside.
  2. The Split: this design does the opposite — it divides each HVAC system into its own separate heating & cooling units. And often they use their own ductwork.
  3. The Stand-alone: this design could be a wall furnace or a singular room heater that does not engage with any other HVAC system or your home ductwork.

What are the pros and cons of each system design? 

Pros of The Package:

  • Less product defection/damage. Every part is manufactured and assembled in the factory. This minimizes the chances of your furnace being damaged or defected.
  • Simpler installation. In fact, the only thing that may need additional installation is extra ductwork.
  • Savings. Combining your heating and cooling systems into a single HVAC unit can save you money on the equipment cost.
  • Easier maintenance. Everything a maintenance technician needs to check is stored in a single unit!

Cons of The Package:

  • Durability. This is major. Because these units are housed outside, they’ll encounter strenuous weather conditions and wildlife damage. These systems will need regular maintenance and potentially more frequent replacement.
  • Liability. With all of your HVAC systems packaged together comes the risk of the entire system breaking down, not just your AC or your heat.
  • Long-term cost. These systems will need regular maintenance and potentially more frequent replacement. This will add up over the long-term.

Pros of The Split:

  • Versatility. These furnace units have the option to be stored in a variety of places in and around your home.
  • Durability. Unlike The Package system, the split system furnace won’t be facing the weather everyday, so it’s likely to last much longer.
  • Accessibility. The control panel on these systems is very easy to access and use, giving you more control over your unit.
  • Savings. Since each heating & cooling system is separately optimized, they can reach much higher efficiency. And because of the control you have over this unit, you’ll be more energy efficient. This can save you money every month over the long-term!
  • Aesthetic. Typically, because they’re better designed, they’re easier on the eyes and ears than the packaged units.

Cons of The Split:

  • Installation. This design is more complicated to install than the package. Why? Because it’s split! It takes a skilled and experienced technician to properly install both the heating & cooling systems. Also, some split systems require you to install the proper ductwork and an air handler.
  • Location. Because the units need to be placed within 30 meters of each other, this type of system may require additional design or components. Think of a tall building, an apartment, etc.

Pros of The Stand-alone:

  • Cost. For example, a wall furnace is relatively cheap overall compared to the other systems.
  • Size. This type of design is great if you’re trying to save space in your home or room because of their compact size.
  • Ease. Simply plug it in and immediately start to feel the warmth!
  • Safety. Many electric stand-alone furnaces have built-in safety precautions.

Cons of The Stand-alone:

  • Inconsistency. Because these systems are smaller and don’t use ductwork, rooms other than the one your furnace is in will not get very warm. This leads to inconsistent temperatures throughout the space.
  • Specific climate. These types of systems are not good for regularly colder climates.
  • Cords. When it comes to an electric furnace, unless you have the perfect spot for it next to an outlet, you’ll need to purchase longer cords.
  • Gas cost and ducts. If you opt for a gas wall furnace instead of an electric one, it’s possible you’ll need to get gas lines installed if they’re not available in your area. Additionally, you may need special ductwork for your stand-alone gas furnace. Both of these things will increase your previously “cheap” stand-alone furnace substantially.

Now that we’ve covered the furnace designs, let’s move on to the different Models/ Blower Motor Speeds.

There are 3 main furnace models/speeds.

  1. The Single Stage
  2. The Two Stage
  3. The Variable Speed
  • Single Stage: This model is also known as the “single speed” because it only has one stage/setting of heat output: HIGH. It has two simple “on” and “off” switches and does not regulate heat output or temperature based on the existing temperature in the space. Think about if your car could only go 100mph, or come to a screeching stop – see the problem? While this model is initially inexpensive to purchase, it doesn’t communicate well with your thermostat, especially if you have a medium-large home. The thermostat may shut the furnace off early, thinking it’s helped achieve your desired temperature. This results in you having to turn the furnace back on, ultimately spiking your energy bill. And because it’s constantly going from 0 to 100, the unit wears out faster, so you’ll replace it sooner. And it usually needs more frequent repairs. However, this model may be a good choice for a small-medium home if you’re just looking to have some extra heat in certain cooler rooms.
  • Two-Stage: This model is known as the “two speed” because, well, it has two speeds: HIGH and LOW. Most of the time, the two-stage furnace will run on LOW, or 65% capacity. When it gets very cold outside, the second stage kicks in and goes into HIGH mode. Imagine your car going 65mph or 100mph or a screeching stop – better, right? These two modes make the two-stage model more energy efficient (thus saving you money) and more accommodating than the single stage. And it usually lasts longer with fewer repairs. However, these models do cost more initially to buy and should be thought of as a long-term investment or solution to your medium-large/multi-story home’s heating needs.
  • Variable Speed: This model is known as the “variable speed” because it’s designed to shift blower speeds, depending on the environment, to control the amount of heat it’s emitting. Imagine a typical car that can accelerate to whatever speed is needed and then decelerate as needed – pretty awesome. The furnace will usually remain “ON”’ even when it’s not actively producing hot air in order to keep the indoor temperature comfortable and evenly distributed. It’s by far the most intelligent, energy efficient, and money-saving over the long haul. You’ll clearly see a difference in your energy bills right away! And because the system gently adjusts speeds, there is significant less wear and tear, repairs, and system failure. So the unit often lasts twice as long as others. However, the upfront cost is more expensive than other units. Depending on your needs, home-size, and budget, this may not be the best route for everyone. But it can have a much lower total cost of ownership! In conclusion, a variable speed furnace should be considered as a long-term commitment and investment in energy savings.

Lastly, we’ve got Fuel Types. This is what will power your furnace.

Each furnace design and model can run off 5 potential fuels:

  1. Natural Gas
  2. Propane/LP
  3. Electric
  4. Wood
  5. Oil

Natural Gas – the most common overall furnace fuel type

  • Pros: powerful, accessible, heat efficient, adaptable to many other home appliances, great for colder climates, and lower fuel cost.
  • Cons: can be a bit pricey and a hassle to install gas lines if you don’t have them, carbon monoxide safety concerns, requires regular & professional maintenance, makes more noise than other options, and may need additional indoor coil.

Propane/LP – the most common furnace fuel type found in rural areas

  • Pros: non-toxic (burns clean), heat efficient, higher heating capacity than others, adaptable to many other home appliances, and fewer fuel deliveries than others because of tank size.
  • Cons: pressurized explosive gas, tank maintenance, safety hazard with tank in yard, high upfront cost to switch to, and possible rental fee.

Electric – one of the most popular furnace fuels

  • Pros: less costly upfront, easy installation, simple maintenance, safer and quieter, good for mild-warm climates, more durable than gas, readily available.
  • Cons: not great for cold-freezing climates, fluctuating fuel cost, usually higher heat cost, less heat efficient, and high cost during coldest months.

Wood – the original type of furnace fuel

  • Pros: widely available, stable cost, relatively low-pollution, net fuel cost is cheaper than some, environmentally friendly.
  • Cons: requires a lot of labor or money to get fuel, requires more space, hassle of disposing ash safely, may need to monitored for safety, higher upfront building & installation cost.

Oil – an all-around average type of furnace fuel

  • Pros: less costly purchase and install, don’t require gas lines, significant heat efficiency, and fairly easy to repair and maintain.
  • Cons: unstable fuel price, requires regular maintenance because of soot build-up, cannot be installed as package system, more difficult to find a qualified technician, and can cause damaging “puff back.”

And depending on the fuel type you choose, that’ll also contribute to the outstanding lifespan of your furnace!

Typically, the lifespan of a furnace ranges between 10-40 years.

And there are other contributing factors that affect the lifespan of your furnace such as:

  • Brand
  • Model
  • Frequency of maintenance
  • Quality of maintenance
  • Humidity levels
  • Proper ventilation
  • Proper installation
  • Climate/Environment

Furnace Cost

At this point you’re probably wondering…

How much do all these different furnaces cost? Are any of them affordable for my budget?

The short answer: YES!

Many of the furnaces we’ve gone over are budget-friendly while still providing basic home comfort.

However, the long answer is that total furnace cost varies greatly. There are number factors that come into play when being able to calculate the total price tag of your furnace.

In general, here are the average unit furnace costs:


Following the cost of the unit, you’ll need to consider other costs such as fuel, installation, and maintenance & repair. All of these will increase your initial unit purchase and it’s up to you to decide which type of furnace best fits your short-term and long-term budget.

On average, here are the estimated installation costs:

Natural Gas units: $3,850*
Propane/LP units: $4,000*
Electric units: $2,500*
Wood units: $2,300*
Oil units: $7,200*

*All of these prices are typically for smaller homes. Larger homes in NC range from $3,8000-$10,000+.


Here are the average fuel costs:

Natural Gas units: $2.36
Propane/LP units: $0.55
Electric units: 10.60 cents per kilowatt hour
Wood units: $150-$400 for a cord of wood
Oil units: $1.32


Lastly, an average HVAC repair costs approximately $295. Electric furnaces are usually $300 or less, while gas furnaces can range from $375-$1,200 because of their complexity. Regular maintenance on your furnace can cost anywhere from $50-$300 depending on your particular system.

In order to get an accurate estimate of your yearly maintenance and repair costs for your furnace, contact Casey Services.

And if you’re wondering how we came up with all these prices, well, remember how we mentioned that there are a number factors that come into play when being able to calculate the total price tag of your furnace?

This is why it can be very difficult to pinpoint exactly how much a furnace costs. During your furnace installation, there are several factors that can affect the total cost.

Factors that can affect the total price tag of your furnace:

  • Home size
  • Fuel type
  • Sunlight
  • Insulation
  • Occupancy
  • Unit quality
  • Other appliances
  • Warranty
  • Climate
  • Brand

If you want to read more in-depth about how each of these individual factors affect your total furnace cost, check out our Furnace Installation page.

So, what’s the BEST FURNACE?!

Well, like the cost of your furnace, that depends! The “best” furnace varies person to person. Your needs and wants dictate the best furnace for YOU.

At Casey Services, we only install American Standard HVAC products. According to Consumer Reports, they’re the #1 most reliable HVAC brand and we can attest to that.

If you want to read more about why we love American Standard’s furnaces, check out our “Why American Standard?” section on our Furnace Installation page.

Happy furnace shopping!