I go to Amazon, search for “air conditioner”, and sort by average customer rating. There’s a couple pages of evaporative coolers (not what I’m looking for), one used window unit (?), and then this:

Average rating: 4.7 out of 5 stars.

However, this air conditioner has a major problem. Take a look at this picture:

Key thing to notice: there is one hose going to the window. Only one.

Why is that significant?

Here’s how this air conditioner works. It sucks in some air from the room. It splits that air into two streams, and pumps heat from one stream to the other - making some air hotter, and some air cooler. The cool air, it blows back into the room. The hot air, it blows out the window.

See the problem yet?

Air is blowing out the window. In order for the room to not end up a vacuum, air has to come back into the room from outside. In practice, houses are very not airtight (we don’t want to suffocate), so air from outside will be pulled in through lots of openings throughout the house. And presumably that air being pulled in from outside is hot; one typically does not use an air conditioner on cool days.

The actual effect of this air conditioner is to make the space right in front of the air conditioner nice and cool, but fill the rest of the house with hot outdoor air. Probably not what one wants from an air conditioner!

Ok, that’s amusing, but the point of this post is not physics-101 level case studies in how not to build an air conditioner. The real fact of interest is that this is apparently the top rated new air conditioner on Amazon. How does such a bad design end up so popular?

One aspect of the story, presumably, is fake reviews. That phenomenon is itself a rich source of insight, but not the point of this post, and definitely not enough to account for the popularity of this air conditioner. The reviews shown on the product page are all “verified purchase”, and mostly 5-stars. There are only 4 one-star reviews (out of 104). If most customers noticed how bad this air conditioner is, I do not think a 4.7 rating would be sustainable. Customers actually do like this air conditioner.

And hey, this air conditioner has a lot going for it! There’s wheels on the bottom, so it’s very portable. Setup is super easy - only one hose to the window, much less fiddly than those two-hose designs where you attach one hose and the other pops off.

Sure, the air...

Air Conditioning