Editing 3044: Humidifier Review

{{comic
| number    = 3044
| date      = January 29, 2025
| title     = Humidifier Review
| image     = humidifier_review_2x.png
| imagesize = 285x287px
| noexpand  = true
| titletext = They should add a little sticker that certifies that the humidifier supports water conservation, but in the sense of energy conservation or momentum conservation.
}}

==Explanation==
{{incomplete|Created by a 101% EFFICIENT TOASTER. This page was clearly autogenerated by an AI that does not understand the comic nor humidity engineering. I tried to improve the first paragraph. Do NOT delete this tag too soon.}}

This comic shows a review of a {{w|humidifier}}, with the reviewer complaining that it uses too much water to increase the humidity of the room to 45%. On the face of it, someone buying a humidifier for the first time might not have an understanding of how much water the device needs, and could be taken by surprise (possibly when their water bill arrives, or by the number of times they are required to manuallg refill its reservoir). The review in the comic has taken it a step further, voicing their complaint as a flaw in this specific humidifier and wishing another model could somehow achieve the same results with less water.

A humidifier works by evaporating water from a tank, causing the air around it to become more humid. The law of {{w|conservation of mass}} states that the amount of matter in the universe must stay constant. Therefore, the amount of water used by the humidifier must be at least the amount gained by the air. Aside from small efficiency improvements (and [[2710: Hydropower Breakthrough|machinery made by Beret Guy]]), it is very hard to reduce the amount of water used to humidify a room without sealing the room better to prevent humid air from leaving it, which has nothing to do with the humidifier.  The humor is thus at the expense of people who don't understand the requirements of their appliances (or other hypothetical services) and complain in ignorance about the impossible not being made possible for their convenience.

Strictly speaking there are other ways to increase the humidity of a room, though all of them are still constrained by the laws of conservation. In theory a humidifier could start a chemical reaction to create water from some other chemicals - which would still need to be supplied. A humidifier could also increase relative humidity by cooling the air, even using no water at all, since humidity (when given as a percentage measure such as the stated 45%) is indirectly relative to the water capacity of the air at its current temperature; however, this is not always viable, and depending on the climate could require more energy than evaporating the water. Unless some chemical or physical reaction was being used to {{w|Endothermic_process|absorb heat}}, the heat would have to be ''transferred'' away.

In principle, a {{w|particle accelerator}} could be used to create protons from energy, either directly, or indirectly as a product of the decay of other particles. Protons are hydrogen nuclei, and could be reacted with oxygen from the air to create water. However, such devices are not conveniently small, consume vast amounts of energy, involve dangerous and inconvenient radiation and magnetic fields, and generate a great deal of heat which would decrease the relative humidity. Thus, they are not a practical method of increasing humidity in a room.{{Citation needed}}

Other examples of commonly-used, commonly-reviewed household devices whose operational efficiency is limited by the laws of physics themselves include {{w|space heater|space heaters}}, {{w|electric water boiler|electric kettles}}, {{w|air conditioning|air conditioners}}, and {{w|refrigerator|refrigerators}}. For instance, a space heater {{what if|35|cannot produce more heat than the electrical energy it consumes}}, as dictated by the laws of thermodynamics. Similarly, an electric kettle cannot heat water with less energy than the amount required to raise its temperature, due to the specific heat capacity of water. Air conditioners and refrigerators operate by transferring heat rather than creating "cold," and their efficiency is constrained by the {{w|Carnot cycle}}, which defines the maximum possible efficiency of a heat engine.

Reviews which indicate the ignorance or [[937:_TornadoGuard|gullibility]] of the reviewer, or which indicate the [[325:_A-Minus-Minus|vindictive nature]] of the vendor, are a common theme in XKCD.

The joke in the title text is based on different senses of the word "conservation". To most people this refers to reducing wasted use of some material, e.g. "water conservation" means avoiding waste of water. But to physicists, it means that some quantity in a system stays the same; for instance, conservation of energy means that energy can neither be created nor destroyed. For many years, most appliances have had {{w|Energy Star}} stickers that indicate their impact on the environment; by adopting the physicists' sense, they can trivially say they support water conservation.

==Transcript==
:[A product review is shown. At the top left is a small drawing of a humidifier within a rectangle. To the right of that rectangle the product name is given. Beneath this is is a line of illegible text, followed by a shorter line of illegible text within a rectangle.]
:HydroPro Humidifier

:[Then below this is a header above a horizontal line that separates the above from a small close-up drawing of Hairy in a circle to the left with two lines of illegible text to his right. Below this is his review (3/5 stars) with a heading and his review text below:]
:Reviews
:★★★☆☆ '''Good but inefficient'''
:It keeps the humidity at 45% pretty well. I'd give it 5 stars if it didn't use so much water.

:[Caption below the panel:]
:My favorite reviews are the ones that penalize products for not violating the laws of physics.

{{comic discussion}}

[[Category:Physics]]
[[Category:Online reviews]]
[[Category:Comics featuring Hairy]]