Cost efficiency: Central cooling vs. window units

[Acsenray]

What’s a more cost-efficient way to cool a house—central air conditioning or a couple of window units?

Say we’re talking about a one-story house, with a half-basement. Total area 1,000 square feet, and the window units would go in two bedrooms.

[beowulff]

The energy efficiency of a central air conditioning system can be substantially better than even the best window AC units.

That said, you might save money with window units, if all you cared about was those two rooms. If you were trying to cool the entire house, the central AC would be cheaper.

[Acsenray]

The linked article seems to say the opposite, at least in the lead.

[Chefguy]

I would never choose a window shaker as my first option. If you’re going to go with cooling just a room or two, have a split unit put in (similar to this). They’re quieter and more efficient than a window unit. For whole house cooling (assuming you have ducted heating), a heat pump connected to the existing ducting is the way to go. Make sure things are sized properly to get the most efficient system possible.

[beowulff]

@Acsenray

The linked article seems to say the opposite, at least in the lead.

Please read it again:

Window-mounted air conditioners (also called room air conditioners) aren’t particularly efficient; the best available models have an EER of about 10 or 11. Central air conditioners (also called whole-house air conditioners or split-system air conditioners) are significantly more efficient; it’s possible to buy one with an EER of 14 or even 15

[Acsenray]

Yabbut. What about this?

Window-Mounted Air Conditioners Save Energy

Compared to homes with central air conditioning, homes with window units have lower cooling costs

[beowulff]

Yes, I think that article says exactly what I said in my first post - you can save money with a window A/C, if you only need it to cool one or two rooms. However, there’s no way that a house cooled by window A/C units will be both as uniformly cool and as inexpensive as one cooled by central A/C.

[ethelbert]

I recently moved from a house where I had window units to a condo with central air. I was happier with the window units (actually in wall units) with the exception of noise generated by the in wall units. I wanted it relatively cool for sleeping and rarely used A/C during the day. In the condo the bedroom is the furthest room from the unit and if I make it as cool as I want it, it means I can hang meat in the rest of the apartment. I agree with Chefguy about the split units. They are the best way to go for a couple of rooms. They are, however, much more expensive than window units.

[Voyager]

@Acsenray

Yabbut. What about this?

You’re both right. I think this is the important part

People living in homes with central air conditioning tend to keep every room in the house cool — even unoccupied rooms — while people living in homes with window-mounted air conditioners are more likely to just cool one or two rooms.
Central air conditioners often have ducts located in unconditioned attics. Research has shown that air conditioning systems with ducts in unconditioned attics have duct losses amounting to about 20% of the air conditioner’s cooling output.
Since window air conditioners are often noisy, homeowners remember to turn them off when they leave a room. By contrast, some homeowners with central air conditioning often leave their air conditioning system on all day, even when the home is unoccupied. As explained in an article by Brian Palmer, “The quiet and unobtrusive functioning of central air conditioners ... can lead to accidental overuse.”

Window units are better because people with central air are lazy and wasteful - according to him.
He doesn’t say about comparably sized houses. Or cooling open layouts, which would be hard to do with window units. And you can use setback thermostats with central units, which could save a lot.

One thing we found when we moved from window units to central units in one house - with central units it is easier to turn off the a/c and open windows on days that are not too hot. If you are in a bedroom with a window unit in the only window you are pretty much stuck running it, if only on fan, even on cooler days.

[Magiver]

I use both. I keep the house somewhat cool with the central unit and use a window unit in my bedroom.