What is a two stage furnace?

the inside of a furnace repair and new air filter

When your HVAC technician installed your home’s furnace, you probably didn’t pay a lot of attention to some of the more technical details. Your concern was keeping your home cool in the summer and warm in the winter. However, if you’ve ever had problems when your furnace just can’t seem to keep up, it’s possible your thermostat is not configured correctly. You may have a one or two-stage furnace, yet your configuration doesn’t reflect that, preventing your HVAC from working correctly.

What does “stage” mean exactly?
First, what does the word “stage” mean exactly? After all, if there are both one and two-stage furnaces, what is that referring to?

The easiest way to explain it is with an analogy. Let’s use a 4×4 pickup truck as our example. A 4×4 comes equipped with a four-wheel drive system. However, you only use this when necessary. No one should drive around using four-wheel drive all the time, as it’s harder on your engine and less efficient.

A furnace stage is just like this. Essentially, it’s a Tim Taylor-esque “more power” level of furnace operation. Each stage is a setting, channeling more power when necessary.

What is a one-stage furnace?
This means that using our previous analogy, a one-stage furnace is akin to a truck that only has a 4×2 drive setting. Even when it would be more helpful, a 4×2 truck will only use the power from the rear axles.

Likewise, a one-stage furnace runs at a continuous level of power, regardless of the outside temperature. 

So what is a two-stage furnace?
A two-stage furnace, therefore, is a furnace system with two levels of power. The first stage will run around 75% of the unit’s full power. When necessary, the second stage will engage and bring the home up to the desired temperature.

Is a two-stage furnace more efficient?
Generally speaking, a two-stage furnace is not more efficient if it runs at full power 100% of the time. Most furnace systems are rated based on the size of the home. Your HVAC technician will select the correct size for your home and its needs. Automatically installing a two-stage furnace won’t necessarily maximize your natural gas usage.

There is an argument that when the weather turns particularly bitter cold, a two-stage furnace will heat your home more effectively — notice we didn’t say efficiently. When it’s cold outside, you’re going to burn more fuel. A one-stage furnace may not be able to keep up with the demands. This is especially true if your home is older and lacks modern HVAC standards (such as a return air vent on your second floor).

Contact us if you’re having problems with your furnace
However, we should point out that any concern or problem with your furnace should be looked at as soon as possible. One homeowner had a two-stage furnace but configured their smart thermostat for a single-stage system. This means they continually fought to keep their home warm. A quick visit from our team would have identified this problem and saved them substantial power costs (by using space heaters throughout their home).
Simply put, there is no problem we’re not willing to help diagnose. Contact us HERE to get started!

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