Is it correct to replace the second temperature by "that" or "it" ?What is this kind of grammar called?

Question

I was reading some samrt apps on a web site. On the web page, the author said this:

This SmartApp enables you to automatically turn your fan on when SmartThings detects the thermostat is off, and the temperature inside your home is hotter than the temperature outside

My teacher used to show us some sentences like this:

I can swim better than you do
My dress is beautiful than yours

So, I am wondering if it is correct to use "that" or "it" to replace the second temperature in the sentence:

The temperature inside your home is hotter than that outside
The temperature inside your home is hotter than it outside

What is this kind of grammar called?

Answer 1

"...the temperature inside your home is hotter than that outside" is correct. The word "that" is a demonstrative pronoun. The app's documentation seems to be choosing to be explicit rather than efficient in its description, a valid stylistic choice.

You could not use "it" here. The word "it" should not normally be used with modifiers. You can't say *"the red it", nor can you say *"it outside"

(note "my dress is more beautiful than yours")