\linebreak causes the words in the preceding line to expand

Question

In a document I have to use \linebreak\indent like this:

\documentclass[a5paper,openany,14pt,oneside,]{extbook}
\usepackage[left=2.34cm, right=2.34cm, top=2.66cm]{geometry}
\setlength{\parskip}{6pt plus 2pt minus 1pt}
\begin{document}
\noindent Wine refrigerator is our newest product on the line. Refrigerated air flows around the bottles to make the wine cool on every side. The thermometer reading must be regularly checked. The temperature is 15 degrees.
\linebreak\indent The refrigerator must be installed in a cool dry place.
\end{document}

When I use it, the words in the preceding line expand like this:

How to prevent that from happening?

System: TeXLive 2020, lualatex

Update In the document, I've used \setlength{\parskip}{6pt plus 2pt minus 1pt} to automatically apply padding space between the paragrahs. I don't know the internals of that line; I use it just because it gets the job done. I've added that line to the Minimal Working Example code.

Update (Workaround solution) Using the TikZ package, adding \tikz[baseline] \node[yshift=5.7pt,inner ysep=0mm,] at (5pt,-2pt) {is 16 degrees.}; works around the problem:

Though it looks fine, this is a workaround solution entailing TikZ If someone comes up with a real solution (i.e. without using TikZ) I would prefer it.

Answer 1

You should not use \linebreak for paragraphs. It sets only an absolute break point, so the line is justified like each other line of a justified paragraph.

You should also not use \newline or \\ for paragraphs. Correct paragraphs are either \par or empty lines in the source code:

\documentclass[a5paper,openany,14pt,oneside,]{extbook}
\usepackage[left=2.34cm, right=2.34cm, top=2.66cm]{geometry}
\begin{document}
\chapter{Wine refrigerator}
Wine refrigerator is our newest product on the line. Refrigerated air flows around the bottles to make the wine cool on every side. The thermometer reading must be regularly checked. The temperature is 15 degrees.
The refrigerator must be installed in a cool dry place.
\end{document}

BTW: a5paper and 14pt is a little bit problematic with justified text. (See the overfull \hbox with the “The” in the example.) But you can improve it, using package microtype:

\documentclass[a5paper,openany,14pt,oneside,]{extbook}
\usepackage[left=2.34cm, right=2.34cm, top=2.66cm]{geometry}
\usepackage{microtype}
\begin{document}
\chapter{Wine refrigerator}
Wine refrigerator is our newest product on the line. Refrigerated air flows around the bottles to make the wine cool on every side. The thermometer reading must be regularly checked. The temperature is 15 degrees.
\par
The refrigerator must be installed in a cool dry place.
\end{document}

---

Edit, because of the changed MWE in the question (after already answering the original question!).

If you don't use \chapter, using extbook and option openany do not make much sense. In this case extarticle would be barely sufficient. So I'm using this class in the following answers.

With the standard classes or gently derived classes like the ext-classes, the best option to use paragraph distance (skip) instead of indenting the first line of a paragraph is the parskip package. In my opinion it also does not make much sense nor is it good style to mix general setting of paragraph skip with some only indented paragraphs. However, you can do it simply using an environment for the indented paragraphs:

\documentclass[a5paper,14pt]{extarticle}
\usepackage[left=2.34cm, right=2.34cm, top=2.66cm]{geometry}
\usepackage[skip=6pt plus 2pt minus 1pt]{parskip}% To use paragraph skip
                                                 % instead of indent.
\usepackage{microtype}
\newenvironment{indentedpar}{%
  \par
  \setlength{\parfillskip}{0pt plus 1fil}%
  \setlength{\parindent}{1em}%
  \setlength{\parskip}{0pt}%
}{%
  \par
}
\begin{document}
Wine refrigerator is our newest product on the line. Refrigerated air flows around the bottles to make the wine cool on every side. The thermometer reading must be regularly checked. The temperature is 15 degrees.
\begin{indentedpar}
  The refrigerator must be installed in a cool dry place.
\end{indentedpar}
\end{document}

But sometimes it makes indeed sense, to use paragraph indent as default and to have a kind of section without title but distance. In this case, defining a special paragraph command would be a good idea:

\documentclass[a5paper,14pt]{extarticle}
\usepackage[left=2.34cm, right=2.34cm, top=2.66cm]{geometry}
\usepackage{microtype}
\newcommand*{\microsection}{\par\medskip\noindent}% Alternatively you can use \smallskip or \bigskip or a \vspace{…}
\usepackage{lipsum}% useful for MWEs
\begin{document}
\lipsum[1]
\microsection
Wine refrigerator is our newest product on the line. Refrigerated air flows around the bottles to make the wine cool on every side. The thermometer reading must be regularly checked. The temperature is 15 degrees.
The refrigerator must be installed in a cool dry place.
\end{document}

Answer 2

The first knowledge about TeX must be: the document is divided by paragraphs, the paragraphs are divided by empty lines in the source file. The text of a single paragraph can de divided to more lines (but without empty lines between them).

You don't need to know any more at this first state, you don't need \hfil\break inside the paragraph (in LaTeX: you don't need \\ nor \linebreak etc. inside the paragraph).

Answer 3

Looking at your desired output it is clear that "The refrigerator.." is a new paragraph as a new line and indent has been understood that way for centuries. So in LaTeX just use a blank line.

Not shown but in comments you also have annonymous sections set off with vertical space and no indent. Again marking those as sections would be the natural markup, I used \subsection level here. You could adjust the space elsewhere

\documentclass[a5paper,openany,14pt,oneside,]{extbook}
\usepackage[left=2.34cm, right=2.34cm, top=2.66cm]{geometry}
\usepackage{microtype}
\begin{document}
\subsection*{}
Wine refrigerator is our newest product on the line. Refrigerated air
flows around the bottles to make the wine cool on every side. The
thermometer reading must be regularly checked. The temperature is 15
degrees.
The refrigerator must be installed in a cool dry place.
\subsection*{}
Wine refrigerator is our newest product on the line. Refrigerated air
flows around the bottles to make the wine cool on every side. The
thermometer reading must be regularly checked. The temperature is 15
degrees.
The refrigerator must be installed in a cool dry place.
\end{document}