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Home » Archive » Why a Mismatched Air Conditioning System is a No‑Go

Why a Mismatched Air Conditioning System is a No‑Go

Photo of a Woman Wearing Two Different Shoes

Should having a mismatched air conditioning system bother you as much as leaving the house wearing two different shoes?

Yes, it should!

Because like a hasty person who hits the road with a sneaker on one foot and a flip-flop on the other, an air conditioning system that is not properly matched will not work efficiently, and will cause you problems in the long run.

In order to understand what we’re talking about, you’ll need to understand what a matched system is. We’ll explain this as we go.

But first, let’s imagine this scenario: it’s a hot day and you have a crisis on your hands: your air conditioner is dead and your technician is recommending a full system replacement.

Being a savvy homeowner, you know that your split air conditioning system is made up of two parts – the indoor unit (air handler or furnace) and the outdoor unit (your air conditioner or heat pump’s condensing unit). In his diagnosis, your technician states that major part of the condensing unit has failed, but the indoor unit is still functioning.

So you ask yourself, wouldn’t I save money by replacing only the faulty outdoor unit?

This is a common question we hear from homeowners. We understand that a “mix-and-match” solution is tempting, especially when money is tight. But if you’re considering going this route, you need to keep reading. We’re going to talk about six reasons why we do not recommend this option to our customers. The first reason being…

1. Indoor and Outdoor Units are Designed to Operate as a Set.

When manufacturers develop their HVAC systems, they design specific indoor units and outdoor units to work together. These are called “matched systems”.  The coils, blowers, wiring, etc. need to be compatible in order for an air conditioning system to operate efficiently and keep your home comfortable.

 If you combine a condensing unit with an air handler (or furnace) it wasn’t designed to work with, in the best case the result will be reduced operating efficiency. In the worst case, the mismatched system may not work at all. Or, it may appear to run initially and then fail after a short time. In all cases, the system’s longevity and efficiency will be compromised.

2. A Mismatched System’s Energy Efficiency Won’t Match Its Label.

SEER2 (Seasonal Energy Efficiency Ratio – SEER2 is the upgraded version of SEER as of 1/1/23) – the rating system representing how energy efficient an HVAC system operates – is based on specific system combinations (matched systems).  So, if your new condenser has an 18 SEER2 efficiency rating, but you combine it with an air handler designed as part of a 14.3 SEER2 system, guess what? The system will not operate at 18 SEER2 efficiency. The newer, higher efficiency unit will be hampered by, and put extra strain on the older, lower efficiency unit.

Also, the current national SEER2 rating standard for air conditioners is 14.3 SEER2 (equal to 15 SEER) for the Southern USA and 13.4 SEER2 (equal to 14 SEER) in the Northern USA. There’s a good chance that your system is not compliant with the current SEER/SEER2 rating standards if it was installed prior to 2023, and especially before 2015 (when the previous national AC energy efficiency standards came into effect). If this is the case, you should replace your entire system to get it up to par.

3. Both Units Need to Support the Same Type of Refrigerant.

Refrigerant is integral to your AC’s cooling process. There are two types of refrigerant in use today: R-22, which will be phased out due to its damaging effect on the earth’s ozone layer, and R-410a, which is R-22’s the more environmentally-friendly replacement.

If your current air conditioner was manufactured before 2010, it probably uses R-22. Most systems built after that use R-410a. If your current system uses R-22, changing out just the air handler or the condensing unit to an R-410a-compatible unit is simply not an option. You’ll need to upgrade the entire system.

This is anyway in your best interest, since R-22 (a.k.a. HCFC-22) was completely phased out by 2020. And, at least you can feel good about helping to save the planet.

4. You’ll End Up Paying More for Installation in the Long Run.

Chances are that both your air handler and condenser were installed at the same time. This means that they’ve been subjected to the same amount of wear and tear. So, even if only one part has failed at this point, you can logically assume that the other part will also fail at some point. Probably sooner rather than later.

When this happens, you’ll have to pay to have the installation crew come out again. In the end, you’ll be paying more than if you’d had both units installed at once.

5. You’ll Miss Out On New Advances in Comfort Technology.

Also, in recent years air conditioners – and particularly indoor units – have advanced. Manufacturers have significantly improved things like noise level, filtering, air handling and overall operating efficiency.

If you install only one part of the system with these new advancements, you’ll negate its positive effects. The old unit simply won’t be able to keep up with the newer, more efficient unit.

6. You’ll Void the Warranty on Your New Unit.

This is one of the main reasons we discourage mismatched systems. Many HVAC manufacturers will not warranty a unit unless it is part of a matched system.  Here’s an excerpt from air conditioning manufacturer, Trane’s, Residential Base Limited Warranty:

“[Under ELIGIBILITY REQUIREMENTS:] Air handlers, air conditioners, heat pumps, cased or uncased coils and stand-alone furnaces must be part of an Air Conditioning, Heating, and Refrigeration Institute rated and matched system…”

This means that if there is a problem with your shiny new unit, Trane’s warranty will not cover the parts unless the outdoor and indoor units are part of a matching “set”.

How Do I Know If I Have a Matched System?

Here’s how you can find out. 

  1. First, ask your installer for an AHRI (Air Conditioning, Heating, and Refrigeration Institute) reference number or AHRI Certificate of Certified Product Performance.
    Or, if you don’t have access to these numbers, you up your system by manufacturer name, model name, and model number. These numbers will be different for your indoor and outdoor unit. You can find this information:
    1. On your warranty
    2. On the invoice from when the system was purchased
    3. Printed directly on the units (or on a label adhered to them)
  2. Go to and enter the information above in this box:
    AHRI Search Bar

AHRI tests, in their own words, “thousands of indoor and outdoor units each year” from many manufacturers. Their testing process serves to verify and certify matched systems and their SEER / SEER2 ratings.

In Conclusion…

With a few workarounds and careful sizing, a mix-and-match system may “work” – at least for awhile. You may even save yourself some money at first. But, like walking around in a pair of matching shoes, a matched AC system will enhance and preserve your comfort. And, most importantly, it will save you more money in the long run.

Of course, we understand that the initial cost of a full system replacement can be hard to swallow when you’re on a tight budget. That’s why we’re here to help make your investment more affordable. We’ll make you aware of available financing opportunities, as well as rebates from manufacturers and power companies like FPL. Plus, we’ll check to see if your current system is still under any type of warranty.

Speaking of rebates – manufacturers often require the purchase of a matched system in order to be eligible for rebates. So this is another reason to upgrade your entire air conditioning system.

If you have any questions about financing, rebates, or warranties, call us today. We’ll be glad to provide you with a free quote on a new air conditioning system for your home.

Do you live in Sarasota or Charlotte County, Florida? Call Kobie Complete at (941) 474-3691 or Fill Out This Form to Get a Free AC Replacement Quote

Kobie Complete’s service area spans from Lakewood Ranch and Sarasota to Punta Gorda. Live in Sarasota and Charlotte County? Fill out the form below or call us at (941) 474-3691 to get a free, no-obligation quote on a new air conditioner installation.

    This form collects your personal information so that we can process and reply to your request for an estimate on a new air conditioner. Check out our Privacy Policy for more details.


    Last Updated: March 23, 2023

    Published on October 26, 2018 - Author: Mallory Gross

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