This blog is going to be all about the different types of air conditioning systems. Not seer ratings, not sizes, not brands, not manufacturers. Types. If you’re looking at your spouse right now, trying to figure out if one of you knows what type of air conditioning system you have, then you most likely have a single stage or one stage air conditioning system. And that’s ok, not great, but ok. It cools the house, right? So I do want to take some time to address two stage, multi-stage, and variable speed systems and how they are different than single stage systems, or more specifically how they help control the humidity. The humidity levels in a home will vary greatly depending on the type of system installed at the home.


Just to quickly address some of those other indicators: Seer rating is an efficiency indicator, not a type indicator. You can have a 15 seer, two stage system that will cool your home better than a 17 seer, single stage system ever could. But we love to talk about seer rating, I think because it’s the easiest thing to understand. The higher the seer rating, lower the power bill. Let’s try to change that so that you and your family can make a more informed decision going forward. And this is one of the most important topics I could ever speak to you about. The humidity levels in your home will vary greatly between the different types of systems.

System SIZE

Size is determined by a mathematical calculation called a heat load. This calculation is based on a multitude of factors including but not limited to, window exposure to the sun, insulation levels in the walls and attic, square footage and ceiling height throughout your home. You’re size of air conditioner is your size. If the heat load calculation was done properly, it will not change until you change something physically about the house. Oversizing your system will cause you to have lower run times and higher humidity. Having too small a system will cause your home to not be able to cool down on the hottest days of the year, not fun. A professional air conditioning company will spend the necessary time to establish what the proper size for your home is. Input by you, the homeowner is also a very valuable tool to determine proper sizing. You don’t have to wait to replace the main air conditioner if you want a certain area colder, by the way. We can help you with getting a much cooler master bedroom as well, if that’s what you’re after.

When it comes to the brands or manufacturers, they all make a single stage, two stage, multi-stage and variable speed air conditioning system. Trane, Rheem, Carrier, Lennox, all of them. We are a very proud Trane dealer if you haven’t heard the show before.


I talk a lot about two stage, multi-stage and variable speed systems and why they are better than one stage systems. This is especially true here in southwest Florida. I say that, because, in essence our homes are all built on top of filled swampland. If you live here year round, you know what kind of humidity we have here from May to October. The biggest thing that needs to be understood from the outset is that your air conditioner is pulling moisture out of your air while cooling your home. So again, the largest byproduct of your air conditioning system cooling your home is it’s ability to pull water out of your homes air, reducing the humidity in the home. That is absolutely critical to understand, so I’m going to say it again a different way. Your a/c system lowers the humidity while it is lowering the temperature. And you want it to, because a less humid home is also a more comfortable home, and a home with better air quality. It is physically impossible in a properly sealed and controlled space like a modern home, to lower your temperature and NOT lower your humidity.

Two Stage Systems

Let’s start with talking about the two stage system. Made by Trane, Carrier, Lennox, Rheem, whomever, they all make them in all sizes. The two stage system has the ability to run at a lower stage than the single stage can, thereby allowing it to run longer, at a lower rate of energy consumption, while pulling more humidity out of your home. However, we set our thermostats based on temperature and not humidity. Why? Because the temperature will fluctuate much less than the relative humidity levels will, operating your system on a much more consistent basis.

Two Stage vs Single Stage Systems

To help us understand how a two stage system works vs a single stage system, let’s use a car analogy. Ok, we have two cars going down the same road, going the same distance. Car A and car B. Car A only has one speed, 70 mph. Car B has two speeds, 35 mph and 70 mph.

If car A is going down the street at 70 mph and car B is going down the street at 35 mph, car A will get there twice as fast, while burning much more gasoline or electricity than car B. Maybe you’re saying “But gas and electricity are cheap, and you know what? I just want to get where I’m going quickly, right?” Everything’s relative.

But what if that car were an air conditioner? Would you still want it to turn on, run at the highest speed, or stage, and shut off? If you don’t care about your humidity levels in your home, sure!

An air conditioner that has a lower gear or stage will run for a longer period of time while pulling out more humidity than an air conditioner with one high gear or one stage ever could. It also does this at a lower energy consumption, but that’s not why you want one. It is a great bonus however.

So if car A were an air conditioner it would be a single stage system. If car B were an air conditioner it would be a two stage system. And all things being equal other than the type of air conditioning system, this could be the difference between a home having 50% relative humidity and that same home having 60% relative humidity. And humidity levels have all to do with comfort as well as indoor air quality.

And this is also critical to understand. The two stage air conditioner or two speed car still has the same high speed that the single stage system does. So, if the heat load rises to the point that it needs to run full speed it can, maintaining the temperature you’ve set on the thermostat. Nothing the customer needs to do, other than hire the right air conditioning company to install and maintain it. We might be able to help you with that.

In fact, Pure Air Conditioning installs more two and multi-stage systems than we do single stage systems. However, we do have a system for every budget, after all it’s your money not ours. But we will show you the respect you deserve and give you all of the options. Not just the single stage ones.

So again, the best thing your air conditioning system does while it’s running, is lower your humidity inside of your home. You want that system to run. You don’t want it running for 3 minutes an hour and shutting off when it’s muggy outside. You want it running at a lower speed that matches the heat load on your home as close as possible, so that it can pull out as much humidity as possible.

Heat Load

Another critical piece of information to understand: The heat load on your home changes throughout the day, by the second. It is literally never the same second to second, however small that difference is. Here’s a dramatic 24 hour example: It rained weirdly at 2 am, then you woke up and it was cool out and overcast in the morning. By noon the sun was out and it was getting hot quickly. It rained again at 3pm, the second time that day, and by evening it was overcast and muggy again. The more speeds or stages your air conditioning system has, the closer it can follow the heat load curve that ever changes throughout the day. And when it can follow that heat load curve closely, it can run at the optimum speed or stage to keep your home at the desired temperature AND the lowest humidity level possible. When it comes to air conditioning the tortoise beats the haire, every single time. And that’s because we would prefer a less humid home over a more humid home.

Variable Speed Systems

Finally, there is a variable speed air conditioning system available for every home regardless of the size. These systems can have upwards of 700 speeds or stages. Truly variable speed, inside and out. Following your homes ever changing heat load curve, minute by minute, second by second, giving you the homeowner the highest level of comfort and air quality you can achieve.

Humidity levels in our homes directly affect our indoor air quality. And indoor air quality directly affects our quality of life.

I hope this information has helped you get better informed on the types of air conditioning systems and will help you make a more informed decision for you and your family.

Mike Crothers – 239-597-7873