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1 Stage Vs 2 Stage Furnace – What’s the difference?

Which of these two types of furnaces is the best solution for your heating requirements?

Let’s take a look at the differences between a single-stage and two-stage furnace, and discover which type is best for you and your home!

I’ve installed hundreds of furnaces for over a decade as a licensed Heating, Ventilation, and Air Conditioning (HVAC) specialist, so you can trust me to know just what makes a fantastic furnace.

Wherever you live in the US, a reliable and effective source of heat during those cold winter months is essential. Even if you already have a traditional fireplace, there are many advantages to installing a gas furnace in your home.

A quality gas furnace will heat your home evenly, effectively, and efficiently. You may have heard that a furnace can be installed as a single-stage or a two-stage system, and both types have their pros and cons.
I’ve compiled this guide to help you understand the differences between a single-stage or two-stage natural gas furnace, and why installing one could be the perfect solution to all your heating needs.

Single Stage Vs Two Stage Furnace: Pros And Cons

Single Stage Furnace Pros
Cost less money upfront
Maximum levels of heating
Great for cold climates
Single Stage Furnace Cons
Outdated design used for older furnaces
Less likely to maintain desired temperature
Not very energy-efficient
Uneven heating throughout the home
Prone to temperature swings
Save less money off your bills
Short-cycling leads to increased component erosion and a shorter lifespan
Two-Stage Furnace Pros
Steady airflow for consistent and even heat distribution
2-stage heating for effective regulation to mild and colder temperatures
Passive air conditioning for improved indoor air quality
Energy-efficient and cost-effective
Lower fans speeds mean quieter operation than a one-stage model
Increased longevity
Great if your home suffers from cold spots
Two-Stage Furnace Cons
Higher upfront cost
Only operates at medium or high power
Not as efficient as variable speed or modulating furnaces

Difference Between Single-Stage and Two-Stage Furnaces

To properly evaluate the difference between single-stage furnaces and two-stage furnaces, it’s useful to first understand how both systems work. 

A single-stage furnace is a simple central heating system that is made up of a heat-producing furnace, a network of pipes installed throughout your home, a fixed gas valve, and a single-speed blower motor

When the furnace is turned on via a thermostat, it runs at full power until it reaches the desired temperature and then automatically turns off. This cycle can produce a quick blast of warm air that’s just what you need in especially cold climates but isn’t great at maintaining this level of comfort and results in uneven heating throughout the home. 

Single-stage furnaces may be affordable, but the advantage of that low initial cost is diminished by higher energy costs in the long run

Some newer models may come with a multi-speed blower motor that can reduce the energy consumption needed to power the furnace, but generally, a one-stage furnace isn’t very energy-efficient. 

They may not be an obsolete heating system, but they’re definitely considered somewhat old-fashioned.

Two-stage furnaces run differently. Although they’re controlled the same way as single-stage furnaces, using a furnace to provide heat to the home through a system of pipes, they offer much greater flexibility by utilizing an intelligent dual-stage gas valve. 

When a dual-stage furnace is switched on, it starts up at an efficient, low-energy setting that is perfect during the fall when temperatures are chilly, but not cold enough to warrant a full power heating cycle. This low setting is also much quieter than a furnace running at full power.

In the winter, when the two-stage gas valve recognizes that the desired temperature set by the thermostat isn’t being reached quickly enough, it will switch to high power and full capacity, working hard to produce the heating output you need. 

By using two heating stages, you’ll have a high-efficiency furnace in the fall, and a high-performance furnace during the winter. 

An extra bonus when using a two-stage furnace over a one-stage furnace is that you’ll have cleaner air throughout your home. 

Since the two-stage furnace cycle is shorter and more frequent, the air is regularly moved around and through the furnace filter so it passively acts as an air conditioner. This filter will also ensure less cool air is blown out as a byproduct. 

An additional humidifier can further increase air conditioning quality. 
This two-stage technology results in even and effective heat distribution with fewer cold spots throughout your home, temperature regulation in the fall accurate to one to two degrees, and a higher energy-efficiency output that means lower energy bills.

Single Stage Vs Two-Stage Furnace Cost

As a general rule, you can expect a single-stage furnace to be less expensive than two-stage furnaces when it comes to upfront cost. If this were the only cost to consider, then you’d have a pretty easy decision to make! But there’s a little more to it than that.

A mid-efficiency single-stage furnace usually costs between $1000 and $1500 by itself, which rises to around $2000 to $3500 with labor and installation included. Although some high-efficiency furnaces can cost closer to $4000, they’re generally considered to be an inexpensive option upfront considering what you get from them.

Two-stage furnaces of a similar efficiency are usually around $500 more expensive up front, so you can expect to pay around $1500 and $2000 for a unit, and $2500 to $4000 with installation. High-efficiency furnaces that use a two-stage valve are around $5000. 

Considering a two-stage furnace is expected to last between 15 to 20 years, this $500 difference can save you hundreds if not thousands of dollars over the course of its lifespan- with considerably lower energy bills, especially if you live in an area with high local energy bill costs. 

Besides the one-stage and two-stage furnaces, there are also variable-speed furnaces on the market, as well as the advanced modulating furnace. These run more efficiently and at any capacity between 40% and 100%, but can cost significantly more upfront, are known to suffer from regular breakdown, and have high furnace replacement and repair costs. 

Modulating furnaces are even more energy-efficient- rated at 98% efficient by most gas suppliers- since a modulating furnace can alter temperature very slowly and much more accurately. 

Because of this a modulating furnace also comes with the highest upfront cost of any furnace on the market. I’d only recommend a modulating furnace if you live in the very coldest climates and can afford the high initial outlay. 

Whichever type of furnace you choose, you may decide to upgrade to a variable-speed blower motor at some point during its lifespan. This can cost around $600 but will ensure a higher-efficiency furnace that can further reduce your energy bills.  

Of course, these costs can also differ depending on the brand you choose to buy from– some more reputable than others. Single-stage or two-stage furnaces from a well-known brand may be more expensive, but you’ll likely be investing in extra quality and durability.

Which Furnace Type Is Right For You?

The furnace type that is right for you will depend on the size of your home and its individual rooms, the climate you reside in, and for some, energy efficiency may be an important factor. There are also extra comfort features to consider that come with many new furnace models. 

The heat energy produced by one-stage or two-stage furnaces is measured in British Thermal Units (BTUs). 

After you’ve measured the size of your home in square feet (multiply the length of each room by its width, and then add the results together), you can use the metric that each square foot of space needs 25 to 30 BTU of heat. 

This can give a reasonably accurate estimate of how much BTU the furnace you choose will need to provide. A two-stage furnace is likely to sufficiently heat a larger home with two or multiple stories. 

If you’re looking for a solution to efficiently heat just one part of a home, it may be worth considering a heat pump instead.

The type of climate your home is in is also important for determining the type of furnace best suited to your home. You can check which climate zone you reside in as designated by the US Government, and then input this along with your home’s square footage to determine more accurately the BTU you should be looking for. 

Generally speaking, a single-stage furnace is better suited to a colder climate, whereas two-stage furnaces can operate at different capacities is better for mild, warmer climates. 

You should also think about how energy-efficient your new furnace will be. As we’ve already seen, single-stage furnaces use energy less efficiently than two-stage furnaces. 

Both single-stage and two-stage furnaces contain a heat exchanger that keeps the inhabitants of your safe from combustion byproducts such as dangerous CO2 gas. 

However, the heat exchanger is prone to metal fatigue, meaning it’s likely to eventually fail. Because two-stage furnaces are considered 90%+ efficient, they contain both a primary and secondary heat exchanger. If the primary heat exchanger fails, the secondary one will immediately kick into life. 

In other words, a two-stage furnace with a secondary heat exchanger could save your life and those of your family!

Who Can Install My 1 Stage Or 2 Stage Furnace?

If you’re buying a new heating system for the first time, it’s unlikely that you have the experience and knowledge provided to install it safely. Some states and cities even have strict laws that mean you are not allowed to install a gas appliance yourself. 

Since a one-stage furnace and two-stage furnaces both require gas and electricity to run, it’s much safer to enlist the help of a specialized and licensed gas fitter. These are fully trained in furnace installation, extension, and repair. 

Although installation costs of a one-stage or two-stage furnace may seem expensive when using a licensed professional, remember that you’re paying for a long-term investment. I’ve seen people install a furnace themselves only for it to blow cool air within a week! 

Proper installation is likely to mean fewer repair costs in the future.

Single-Stage Furnace Vs Two-Stage Furnace: Frequently Asked Questions

Is A Two-Stage Furnace Worth It?

If you own a larger home, then a dual-stage furnace is definitely worth the investment. You’ll benefit from lower energy bills and even temperature distribution– even during those cold winter months. If you can stretch your budget, variable speed and advanced modulating furnaces offer even more savings.

How Much Energy Does A Two-Stage Furnace Save?

Because of the more efficient way a two-stage furnace turns energy into heat compared to one-stage furnaces, with less fuel burned, and the ability to run at medium and high capacities, they regularly use around 3% less energy

You’ll certainly be saving money off your energy bills in the long run.

However, if you live in a colder climate where heating in mild or warmer temperatures isn’t needed, then these savings are negligible. They also aren’t as efficient as modulating furnaces, which you should consider if you don’t mind the significantly higher upfront cost. 

My Final Thoughts

The main difference between one-stage and two-stage air conditioners is their flexibility. Whilst a one-stage furnace can provide high levels of heat for colder climates at a low upfront cost, a two-stage model can accurately regulate your home temperature in mild and warmer climates. 

Given all the extra advantages that two-stage furnaces have over a single-stage furnace, and considering the relatively small price difference between these two furnace types, I’d confidently recommend a two-stage furnace for all but those on the tightest of budgets.