The Power of 2 Stage HVAC Systems

Imagine riding across town on a bicycle that has one gear. It would be great if the road was flat all the way through. But the first time you hit a big hill, you would probably wish you had a second, lower gear so you could keep pedaling at a smooth, consistent pace. It’s the same with your HVAC system.

For a century or more, heating and cooling systems have been designed like that bicycle — with one gear. They run at full speed and capacity until your home reaches your desired temperature. Then, they shut down until the next time you need heating or cooling. These single stage systems certainly get the job done, but the result is a wave of up and down temperature swings that are not as comfortable or energy efficient as they could be. That’s why 2 stage HVAC systems are such a good idea.

2-stage HVAC systems are kind of like a bicycle with two gears — one for full speed, and another for maintaining comfort with less effort. As a result, they can heat and cool your home with a nearly continuous wave of consistent comfort.

As the world's leader in heating & cooling basics, Carrier offers a number of 2-stage systems that can provide steady, consistent comfort, save on energy bills, keep humidity levels under control during the summer months and more.

What Is a 2 Stage HVAC System?

A two stage HVAC system is equipped to adjust operation for high stage or low stage heating or cooling, depending on the comfort demands of your home. Most types of systems — furnaces, air conditioners and heat pumps — are available as two stage models.

High stage is basically full capacity operation. On high stage, your system delivers 100% of its heating or cooling output, much like a single stage system. High stage is used less often, like when temperatures outside become more extreme, or at start-up to reach your desired temperature more quickly.

Low stage is a reduced heating or cooling output, usually about 60% - 70% of full capacity. A majority of the time, low stage output can easily maintain your desired temperature. Because the system is not operating at full capacity, it is using less energy.

Two stage systems often include variable speed blower fans which can match airflow to comfort demands. They also have “smart” electronics that monitor conditions and automatically select the best stage for comfort and efficiency.

Benefits of 2 Stage HVAC Systems

Two stage systems provide several advantages when compared to traditional single stage setups:

Comfort — Indoor temperature remains more consistent. Nearly continuous flow of heated or cooled air helps minimize cold or hot spots in your home. The system automatically selects the best stage as conditions change — full capacity for more extreme conditions, reduced capacity for maintaining comfort.

Energy efficiency — By operating on low stage a majority of the time, two-stage systems can help reduce your heating and cooling energy bills.

Quieter operation — When running on low stage, fans are quieter, and the sound of air flowing through your ductwork is reduced as well.

Humidity control — During the hot, humid summer months, your air conditioner or heat pump acts as a dehumidifier. 2-stage systems running nearly continuously draw more moisture from humid indoor air.

Air quality — With nearly continuous operation, air flows through the system’s air filter with greater frequency, allowing the filter to trap more airborne particles.

Reduced wear & tear — 2-stage systems are easier on the equipment in three ways: fewer on-and-off cycles puts less stress on moving parts; running at reduced capacity is less taxing to fans and compressors; cleaner air running through the system can also be beneficial to the lifespan of the equipment.

Best 2 Stage HVAC Systems for Your Home

2 stage HVAC systems can provide the perfect fit for a variety of needs and budgets. If you want the most efficient system available, be sure to check the efficiency ratings. For an AC unit, look for the SEER2 rating. For heat pumps, look for HSPF2. And for furnaces, it’s AFUE. Like miles-per-gallon for a car, the higher the rating, the more efficient it is.

Many of Carrier's Performance Series models are two-stage HVAC unit. Learn more about Carrier's offering for 2 stage air conditioners, 2 stage heat pumps, and 2 stage furnaces.

The climate where you live can affect your choice as well. For warmer climates, consider a heat pump system or an air conditioner with either a furnace or auxiliary heat. In colder climates, a furnace combined with either an air conditioner or heat pump would be a typical choice.

If budget is your main consideration, look for standard efficiency models with fewer “extras”.

Also, remember that heating and cooling systems aren’t a “one-size-fits-all” proposition. The size of your home can affect which models will provide the comfort you need. As you get closer to a final decision, be sure to work with a qualified HVAC professional to get a system that is properly sized for your home.

Installation and HVAC Maintenance Tips

To make sure your 2 stage furnace, heat pump or air conditioner runs efficiently and effectively for years to come, be sure to follow our recommendations on HVAC maintenance, furnace maintenance, air conditioner maintenance, and heat pump maintenance. 

Two stage systems follow many of the same basic procedures as single stage systems. That includes regularly replacing the system’s air filter. Learn more about how often to change your air filter and how to change your air filter. It also includes having your system cleaned, checked and tuned up annually by your local Carrier dealer.