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Q&A Spotlight

Central Air Conditioning vs. Window Units

Pros and cons of central AC vs. window-mounted units

Choosing between a central AC system and multiple window-mounted units is a matter of cost, energy efficiency, and aesthetics. Image credit: Florida Solar Energy Study

Is there a good reason to install an expensive central air conditioning system rather than window units with equivalent capacity at a fraction of the cost? It may depend on where you live. Phoenix homeowner kurtgranroth writes in this Q&A thread that he doesn’t have a solid answer for that question. He presents his case:

“Our home requires about 5 tons of cooling to keep us comfortable in our egregiously hot summers. This figure comes from a Manual J calculation. I recently replaced both of my (failing) units with two 3-ton Bosch IDP Inverter heat pumps with 18 SEER2 / 11.2 EER2 efficiency, at a cost of just under $30k. I could have saved a few thousand dollars by replacing them with two Trane 16 SEER2 heat pumps at $25k.” He goes on to say that he has a Midea U-shared Inverter Window AC unit that sees limited use, is extremely quiet and energy efficient, and has a rating of 15 CEER.

“Apparently CEER isn’t directly comparable to either SEER or EER but it’s closer to EER, and my understanding is that 15 CEER puts it up into the ductless minisplit territory. These units don’t have a reversing valve, so they are strictly for cooling with no heating capacity. That’s not a big deterrent, as Phoenix is in a cooling-dominated climate.”

He continues: “A 1-ton Midea Inverter Window AC costs $450. I could get the equivalent cooling tonnage as my existing two Bosch units by buying six Medea units and distributing them around my house—in both cases I’d have 6 tons of cooling.

Cost of central cooling: $30,000
Cost of window-unit cooling: $2700

The window unit pricing is less than 1/10 the cost of the larger systems, for the same cooling capacity. Even if my 18 SEER2 units are more efficient, I…

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  1. nickdefabrizio | | #1

    In a hot dry climate like that, why not go to mini splits? He can buy a DIY Perfect Aire or MrCool multi head mini split, or better yet, 4 Perfect Aire or MrCool DIY single head mini splits: 23 SEER- at around $2000 each head and install them himself. Or do what I did and buy Fujitsu super efficient (30 SEER) single head mini splits and do most of the install but have an HVAC guy do the final line charge. Using this method, I have Fujitsu units that cost me around $2500 each. They have been a great value...They work great for heating and cooling...though mediocre for dehumidification.

    One thing I noticed recently: when people are doing HVAC or Solar cost /benefit analyses, they are not fully taking into account the fact that interest rates have gone way up. If you can get 5% on treasury bills/notes, and mortgage rates are 7%, the "carrying cost" of a large up front expenditure (whether you pay cash and lose interest income, or must borrow the money and pay mortgage interest) is much higher than what we have enjoyed for over a decade. Thus, the "break even" point in energy cost savings has gone higher . Of course in some areas energy costs are also going up so this offsets the higher carrying costs somewhat. .

    1. kurtgranroth | | #2

      I actually did go with a Mr Cool mini split for the guest house I built and love it -- good price, easy to install, and works great. That wasn't an option for the main house since I'm not a huge fan of the look of the heads and my wife completely forbids it. We did get a quote for a ducted mini split installation instead of replacing our central heat pumps and the cost was considerably higher.

      Also worth noting, too, that the inverter window units are still a third to a quarter the cost of an equivalent DIY mini split for equivalent tonnage and if both are considered equally aesthetically unappealing (personal choice) and both can fit in a space, then mini splits have only a few advantages over the window units...

      1. nickdefabrizio | | #3

        Understood. My wife was also pushing back on wall mounted units; but allowed me initially to install one unit. Now she loves the ability to control the heat and soon she forgot about the "look" of the wall mounted units so I added a few more

        Note that MrCool now has an in- ceiling cassette for the 4th Generation unit that looks great and solves the problem of appearance. I don't know how much of a performance penalty there is on it. It is a bit more expensive than a wall unit. .

  2. Deleted | | #4


  3. acrobaticnurse | | #5

    It's interesting to see it claimed that central air/heat affords the benefit of being able to add an ERV  and dehumidifier when often it's recommended that such equipment have its own ductwork. Someone could utilize multiple Midea u shaped window ACs and have a ducted ERV/dehumidifier that also serves to reduce hot/cold spots as air is circulated. I recently added a window AC to one of our bedrooms because it takes so little power and is 120 volts so I can run it on my smaller generator in the case of a power outage, as I did last month. The 8000 btu Midea generally uses 100-200 watts and maxes out at 450 watts. I have a central heat pump that works well but I have to use a larger (and louder) 240 volt generator that requires ~3 times as much propane per hour in order to run it. A 120v mini split could also work but would cost more and install would be more involved. 

    It's also interesting to think of having to uninstall/reinstall a window AC yearly. Where I am in NC people leave them in year-round. The house I grew up in had 3 window ACs for cooling though usually only 1 or 2 were on at a time and a wood stove for heat. My grandparents next door used a kerosene space heater in the winter and 1-3 window ACs in the summer. In both our and their case one of the ACs was larger at maybe 12,000 BTU and the others were small at maybe 5-8,000 btu, and we never had them all on at once. 

    I like the aesthetics of central air/heat and not having to build/maintain a fire and not having every window be partially blocked by a window AC. It's also easier to air seal without a window AC, though the Midea U shaped AC has a good weather stripping kit that I wouldn't want to be taking out every year. I can understand paying $30k for a quiet and efficient heat pump, ERV, and ducted dehumidifier to keep a 2-3,000 square foot home comfortable year round, though I get the impression from online videos and comments that many are expected to spend that much for just the heat and AC alone. I'd likely opt for DIY mini splits and a separately ducted Santa Fe dehumidifier that also brings in fresh air in that case.

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