Multiple window units instead of central HVAC?
What are the compelling reasons for spending five figures installing central HVAC rather than a fraction of that installing the equivalent tonnage of window units?
This question was raised by a person I follow online and I realized that I don’t have a good answer for that, beyond “aesthetics” and maybe “hard to find a heat pump heater window unit”.
Here’s a case study. My Phoenix 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) packaged units with two 3 Ton Bosch IDP Inverter heat pumps with 18 SEER2 / 11.2 EER2 efficiency. It cost just shy of $30k. I could have saved a few thousand by replacing them with two Trane 16 SEER2 heat pumps at $25k.
I happen to have a Midea U-shared Inverter Window A/C unit for a limited use case and in that use case, it’s been working amazingly well. They really are extremely quiet and notably power efficient — its rated at 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 mini split territory. These units don’t have a reversing valve so they are strictly cooling with no heating capacity. That’s not a big a detriment as it might seem since cooling dominates the year in Phoenix.
A 1 Ton Midea Inverter Window A/C runs $450.
So… super simple math. I could get the equivalent cooling tonnage as my existing two Bosch units by buying six Medea units and spreading them around my house — it both cases I’d have 6 tons of cooling.
Cost of central HVAC: $30,000
Cost of window HVAC: $2,700
The window units are less than 1/10 the cost of their big brother for the same cooling capacity. Even if my 18 SEER2 units are more efficient, I could never come close to making up that cost difference in even 20 years of running costs.
So when my current heat pumps finally die, what compelling reason is there for me to replace them in-place versus spending a fraction in equivalent window units?
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This may not be the only reason to install central ductwork but with ductwork you can install whole house air filters, supply fresh air with ERV’s and use a supplemental humidifier or dehumidifier. It also better handles the load in really small rooms like powder baths to allow more even heating and cooling behind closed doors. I’m not saying all of that justifies the cost. In days past the cost differential was not as high as it seems to be now.
Window units tend to be built for a very low price point and thus tend to be not very efficient and not very durable.
They’re cheaper for sure, and have been for decades. If they haven’t been widely installed by now, I think it’s safe to say buyers don’t want them.
You can make similar arguments for lots of things:
- In room space heaters vs. central forced air/hydronic/whatever
- Bathtub + tub surround vs. tiled shower
- Hot plates and toaster ovens vs. nice range
- Oscillating fan vs. ceiling fan
... and the list goes on.
The fact of the matter is, people care (and therefore value) aesthetics and integration. To deliberately channel your example, PTAC units are found in all sorts of hotel rooms, but once you get above a certain "level" of hotel, they're nowhere to be found.
It seems some people object to the aesthetics of having the unit stuck in the window opening. That may or may not be a compelling consideration given the economics and your situation. I'm thinking along other lines. At least for new construction why not design in from the start dedicated openings matched to the units? And depending on the details of your existing house it could possibly be retrofitted into existing construction.
The final result wouldn't look all that different (at least from the inside) from the mini-split systems currently popular.
I also like the ease by which you could zone your house. No fancy, complicated centralized electronics.
I’ve seen this done before, but it’s unpopular. Ductwork is just better and people are willing to pay for it.
I've seen too many filthy ducts. If there is an option that requires less maintenance I would at least consider it.
If ducts are dirty, the overall system is broken. When you have sealed ducts, sealed equipment, and proper return air filtration, ducts are pristine.
Kurt,
Eleven years ago I wrote an article on this topic. I reached the same conclusion that you did. Here is a link to the article: "Window-Mounted Air Conditioners Save Energy."
I switched from a split AC to a window unit on my first floor and it works like a charm. 1450 square foot 1st floor, open concept, with 9ft ceilings, house built in 2005, not super insulated or built with air sealing in mind but the walls are 2x6 so have R21 in them. Location is Long Island,, NY. Inverter technology has made window units much quieter, particularly when run on low. The unit is a duel hose portable with inverter compressor that is using 3.5 to 4 kw day. This is much less than the 4ton R22 attic (vented)ducted unit it replaced (I don’t have energy usage for that old system but it had to be more) I have no doubt my energy consumption will go up when I replace the old R22 system so I am not chomping at the bit to do it. In addition, I avoid paying annual maintenance costs for a new split AC.
Drawbacks:
1) ugly
2) annual set-up and take down of the unit for cooling season. I have split ACs serving my 2nd floor and it is much easier to flip the switch on my thermostats for cooling season.
3) can’t filter the air like I do with my upstairs split ACs.
Noise is not on the list as it sounds like a fan when running on low. I have more noise from my poorly commissioned split AC’s on my second floor.
Love this question. There are all sorts of technical aspects to the answer, but maybe most critically it shows how our values (morals, politics, expectations for convenience, etc.) often dwarf other considerations. Like Patrick (#4) pointed out, we make similar decisions in our houses all the time. I'd extend that to contractors who drive a new F250 when a used Dodge Caravan might do the same thing, or a restaurant meal that costs us ten times the home-cooked version. How often do we interrogate that Americans expect a thousand square feet of house--each?
Why are we willing to spend up by an order of magnitude (or more) to achieve more or less the same result? And they call us climate activists irrational.
If this forum had "like" buttons for comments I would be "liking" yours. I think it's great people ask questions like this as well. Of course, sometimes the norm is the right thing to do. But if we keep following the norm simply because it's the norm we are probably missing opportunities to do better.