diff --git a/bib/glossaries/symbols/subscripts.bib b/bib/glossaries/symbols/subscripts.bib
index 4caf238..a8da2e7 100644
--- a/bib/glossaries/symbols/subscripts.bib
+++ b/bib/glossaries/symbols/subscripts.bib
@@ -17,4 +17,8 @@ @symbol{air
 @symbol{electric,
     name={\text{el.}},
     description={electric},
-}
\ No newline at end of file
+}
+@symbol{thermal,
+    name={\text{th}},
+    description={thermal},
+}
diff --git a/chapters/mainmatter/base-features.tex b/chapters/mainmatter/base-features.tex
index 7ca4fe0..b155a80 100644
--- a/chapters/mainmatter/base-features.tex
+++ b/chapters/mainmatter/base-features.tex
@@ -480,6 +480,9 @@ \subsubsection{Physical Units}
 The mode in which units with negative exponents are displayed can be changed,
 \iecfeg{e.g.}\ fractions can be used:
 \si[per-mode=fraction]{\meter\cubed\kelvin\per\kilogram\squared\per\giga\watt\per\degreeCelsius}.
+You can also use \verb|\DeclareSIQualifier| to create textual subscripts for units,
+further specifying them, or create entirely custom units using \verb|\DeclareSIUnit|.
+An example for both combined is: \si[per-mode=fraction]{\mega\watthour\thermal\per\meter\cubed}.
 
 The \verb|\SI{<quantity>}{<unit>}| command essentially combines \verb|\num| and
 \verb|\si|, inserting a small space in between, for correct typesetting.
diff --git a/cookbook.cls b/cookbook.cls
index d839c50..5099df9 100644
--- a/cookbook.cls
+++ b/cookbook.cls
@@ -1655,7 +1655,7 @@
     % Declare units ourselves:
     % Set as text so it stays a hyphen in math mode, as opposed to minus sign
     \DeclareSIUnit{\volpercent}{Vol.\text{-}\%}
-    \DeclareSIUnit{\kilowatthour}{kWh}%
+    \DeclareSIUnit{\watthour}{Wh}%
     \DeclareSIUnit{\annum}{a}%
     \DeclareSIUnit{\atmosphere}{atm}%
     \DeclareSIUnit{\partspermillion}{ppm}%
@@ -1669,6 +1669,9 @@
     \DeclareSIQualifier{\water}{%
         \glsfmtname{sub.water}%
     }
+    \DeclareSIQualifier{\thermal}{%
+        \glsfmtname{sub.thermal}%
+    }
 
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