Are Multi-Stage Air Conditioners Better than Single Stage Air Conditioners?

A question we get asked about quite often is: Are multi-stage air conditioners better than single-stage air conditioners? I think the best answer to that is it depends on what part of the country you live in.

  • Use multi-stage air conditioners in some areas to intentionally run the air conditioner for longer in an effort to remove more humidity as the air conditioner is running.
  • In areas that have no humidity issues whatsoever, the only thing you want to do is cool your house as quickly as possible.

Benefits and Downsides

  • There is no harm in installing a multi-stage air conditioner in an area that, in our opinion, doesn’t need one. There are other benefits besides additional humidity removal such as:
    1. A lower noise level outside as it’s running
    2. More cold air distribution because the fan will run for a much longer period of time to cool your
      home. So, you will generally get a better temperature distribution throughout the house.
  • The downside to having a multi-stage air conditioner where one is not needed is
    1. Additional potential repair costs with having more parts inside the machine (oftentimes, multiple
      compressors inside of the air conditioner itself).
    2. The high stage on a two-stage air conditioner is noisier than a single stage air conditioner would be.
    3. And of course the additional upfront cost of owning the unit.

Confusion and Solution

Conversely to the Pacific Northwest, if you’re in areas like much of the east coast where humidity is a primary concern, a multi-stage air conditioner is a fantastic solution. The confusion for the consumers comes with the assumption that spending more money on equipment is always the better choice. Oftentimes, it is a better choice, but not every time. This is a good example of more expensive equipment not being the best choice depending on what region of the country you’re in.

FurnaceUSA is here to provide you with excellent service & installation, whether it’s a multi or single stage air conditioner! Contact us today:

Are Multi-Stage Furnaces Better Than Single Stage Furnaces?

A common misperception that customers have is that having a multi-stage furnace is what makes the furnace more efficient. Although it may at the margin, any benefits from a multi-stage furnace are not primarily related to fuel savings.

Comparing Furnace Models

  • The primary people who can benefit from multi-stage furnaces are customers who are trying to prevent temperature swings in their house.
  • An analogy would be: A single stage furnace is comparable to having a car that you can only floor the gas pedal or have it completely off. It gets you to where you want to go, but it will often overshoot the target, causing temperature swings and temperature fluctuations.
  • A single-stage furnace has been the predominant method of heating for the last half century and has worked well.
  • Some years back, they developed two-stage furnaces; the instant and most obvious benefit to a two-stage furnace is that the majority of the time, it runs at a much lower capacity while reserving the higher capacity for either when it gets colder or the furnace has been running for a longer period of time.


  • If a thermostat calls for heat and the furnace only fires up at 50% or 60% capacity, it more slowly brings the temperature up and is much less likely to overshoot the target. Because the fan has been running for a longer duration, it gives a better chance for the air to equalize in temperature throughout the house.
  • It’s important to note multi-stage does not just refer to fuel consumption, but a properly set up furnace will also adjust the fan speed to coincide with the adjustment in the fuel usage to keep the temperature rise relatively equal. (‘Temperature rise’ referring to differential in the air temperature entering the furnace and the air temperature leaving the furnace.)
  • Adjusting only the fuel and not the fan speed would cause the temperature in the furnace to be far too hot or too cold.

Variable Stage Furnaces

  • After multi-stage were invented, then came out variable stage with some models offering 60 stages and some models offering up to 100 stages with completely variable output up and down the spectrum.
  • This can sometimes lead to some negative consequences that were not anticipated well with manufacturers.
  • For instance: When furnaces modulate down too low and modulate the fan speed down too low, the fan size can be undersized for the size of the house in retrofit applications because the duct work system was not designed perfectly and the ducts are difficult to adjust as they’re buried in floors, walls and ceilings.


Our recommendation is to use two-stage furnaces for the vast majority of applications.

Top Tips to Consider When Buying A New Furnace

There are a variety of factors to consider when you are looking at purchasing a new furnace for your home.


One of the first things people consider when purchasing a furnace for their home is the brand. But this is actually one of the least important factors.

In our opinion, as long as you are dealing with one of the major brands, like Lennox, Carrier, Goodman, etc. – you are going to be fine! The key is, you just want the brand to be supported in the area. For instance, if the furnace were to break down in five or ten years’ time, you just need to have access to available parts, or more specifically, whatever company is repairing the furnace must be able to access the parts readily.

To think that some furnaces break down and some don’t is a bit of a stretch. The truth is, there’s probably a 10% variance between the best and the worst furnace in terms of likelihood of breakdown.

Noise level

Another factor people consider when purchasing a new furnace for their home is the noise level. This more specifically relates to the technology that you are installing vs. the brand of furnace. So, if you are looking for something quieter, you want to make sure you are putting in something high-efficiency, as it’s a different technology compared to what a mid-efficiency or low-efficiency is. High-efficiency takes all the potential sound and traps it in the furnace and sometimes transfers that sound outside.

Size of the new equipment being installed

Another factor that homeowner should not be worried about, but still you should be aware of – how the decisions are made – is the size of the new equipment being installed. You can’t rely on things online for the most part, because depending on the average winter temperature in your area, it will greatly impact what equipment gets installed. Sizing is based on the ‘winter design temperature’ for your area. Roughly meaning, what is the coldest it will ever get in your area? It needs to be able to heat at that temperature. So, the vast majority of the time, the maximum potential of the furnace is not needed and will never be used.

It is much more common for contractors to oversize a piece of equipment than to undersize it. And oversizing can lead to all sorts of negative effects, like prematurely wearing the furnace out, noise issues because the fan is too big and a variety of other factors.

One sub-category of the sizing issue is, there are two different things to size on the furnace: “the gas-sizing” and “the fan-sizing”. If you overdo the fan-sizing that will lead to problems, but if you underdo the fan-sizing, there won’t be enough air to push to the furthest parts of your home.

As a quick rule of thumb, I would suggest under-sizing on the gas, from what you think it is, and oversizing on the air flow. One of the best ways that we can do it is just to contact our sizing department and free of charge we will walk you through how we size the equipment.

How to remove air from your boiler system

Having air in your boiler system, also known as a hydronic heating system, is among the most common issues that you’ll get with a boiler. But the first issue you need to resolve is why you are having an air issue in the first place.

It’s normal, when you first commission a system, to get a little bit of an air issue. The reason behind this is that new water (H2O, the O part of it being oxygen), when introduced, has a significant portion of air in it. However, over time the air is slowly removed with automatic air vents, and/or an air scrubber. So, the very best type of water in your boiler system is actually dead oxygen-free water, which takes a period of time to accomplish.

The question is if your system is not new, if it is years old, and it’s developing an air issue, what causes that? One of the most common causes of it is a leak somewhere in your system, and new water is being replaced into the system, and with that new water comes new air. Another common cause is if you have a certain kind of piping system, commonly known as a polybutylene piping system, or a poly-b piping system, that absorbs air from the walls of the pipe. This type of piping system was banned back in about 2000.

The minor negative effect of having air in a boiler system is that it can make zones stop working. A major negative effect of having air in the system is that it can damage almost everything in the system and can make things rust out. This is because mixing air and water together causes non-ferrous or rustable metals to get destroyed. That often means the boiler itself will get destroyed. Boilers and boiler components rely on the fact that there is virtually no air left in the system and that allows them to not rust away.

So, as long as you’ve addressed the reason of why there is air in the system, getting the air out of the system can either be a simple thing or a complex thing. The first thing to look for is up on the radiators against the wall. Sometimes at one or either end you’ll see a little slotted screwdriver port. If you put a screwdriver in there and turn it about a quarter turn, it can open up, releasing the air.

At that point in time you must be sure that the air bleeds out and not a lot of water bleeds out, and that you turn the port back down so that water no longer comes out, as this can cause damage to your home. Releasing a little bit of air is often enough to unblock a zone from circulating water. That’s essentially what happens. Zones get blocked from water passing through because there is air trapped in the zone at a high point.

The more complicated way to get air out of a system to physically force it out and flush it out, with new fresh water. This is more complicated than it seems as it requires the boiler to be shut off, and certain shut offs to be turned off on the boiler system, to force the water through the exact zone that you want the water forced through. If it comes to that point, unless you are a HVAC technician, I would suggest that you call a company. There are many ways that you can damage your system at this point in time by doing the wrong thing.

The truth about geothermal heating

People often ask us about geothermal heating, as there are many fantastical claims out there about how efficient it is, and how much money it can save you in utility expenses. The truth, in this case, comes in multiple parts.

Indeed, geothermal heating system – installed correctly – can give you the most efficient heating arrangement that you can possibly get. Geothermal heating works, but it usually works by installing a network of pipes under the ground, thereby absorbing the heat under the ground, and bringing that heat inside, or doing the reverse when it’s in the cooling mode.

Geothermal efficiency explained

The reason why it can be so efficient is this: the air-source heat pump exchanges the heat with the air outside, and the air could go down to a freezing level. However, underground remains relatively even in temperature, somewhere in the mid-50s Fahrenheit. So, there’s a lot more heat that you can extract out of the ground than you can pull out of other sources.

Downside of Geothermal

  1. The challenges, however, come in multiple forms. The first and the most problematic issue is that it is significantly more expensive to install a ground-source geothermal system as opposed to an air-source system. If you think about it, an air-source air conditioner just needs to be put next to a house, the piping connected to the furnace, a coil installed properly, some electrical wiring done, and the system is ready to go. A ground-source system can take weeks to install, might involve a reconstruction of your entire property, including drilling of wells in the ground and many other major activities.The problem here is that geothermal heating systems drive up the installation and material costs to a very high level, which, unless you’re planning on being in the house for 40 or more years, makes it hardly a cost-effective solution; most probably you will never recoup the money that you spend in the process.
  2. Another negative aspect of geothermal heating, in our opinion, is the relatively minuscule number of people that know how to work on them. From my experience, I would estimate that for every 1000 technicians that can work on conventional heating or cooling systems, there may be 1 person who is qualified to work on a geothermal system. If you’ve ever had an issue at home that required fixing, you know how long you have to wait until the repair person shows up. Imagine the same situation, but there are 1000 times less specialists available. We’ve had to go in many times and disable a geothermal system, and put in a conventional system instead, because the clients were so frustrated with not having it working how they thought it was going to function.


I think geothermal heating does have a bright future, but it is going to require the systems to be streamlined and simplified, and manufactured by the largest manufacturers in the world to drastically expand how many people service them, install them and work on them. It is a heating source of the future, but it will take many years until it becomes an economically feasible solution.